Dual-zone AC in camper van

[Gerrbear]

Hi,

I have a 1986 VW Westfalia camper van that I'd like to add AC to. My van has never had AC, but it was available as a factory or dealer-added option. The factory AC was installed in the rear of the van (it is a rear-engine vehicle), and the dealer-added system was installed behind the dash in place of the glove box.

From what I have heard and read from people with either of these systems is that they are inadequate to maintain comfortable temperatures for all passengers; either the passengers near the AC fans are freezing to keep the others cool, or the others are too warm. I would like to solve these problems by installing a dual-zone system with two evaporators/blowers with individual controls for each. However, while I am capable of doing all the manual work, I don't know how to design the system.

My plan is to run the whole system off of one compressor (a Zexel 150 cc unit that is factory-installed with the 2.5L Subaru engine I have installed in the van). I would then run an AC line to the front of the van to a parallel-flow condenser I will install in front of the radiator. From there I would run a line to a receiver/drier/accumulator (I don't know which is needed), and after that a tee to each evaporator (with an orifice tube/expansion valve). Then from there the lines would tee back together and return to the compressor.

My questions are:
- does the above make sense?
- is just one receiver/drier/accumulator sufficient? Which do I need?
- I think I need an orifice tube in the front (primary system) and an expansion valve in the back(secondary system). Is that correct?
- I was planning on putting solenoid valves downstream of the tee after the accumulator to only allow refrigerant flow through the circuit(s) that are on use. Will that be enough to prevent one evaporator from freezing up while the other is in use?
- should I run the same evaporators in both circuits, or can they be different? Can I run any combo of evaporators or do I need to size them in relation to each other?
- where would I need to put the trinary switch(es)?
- other than hi/low ports and all the controls, is there anything else I need?
- I was planning on using off-the-shelf Evap/blower units from a place like vintageair.com or nostalgic air.com to make the controls easy, will I need additional controls?
- anything else I'm missing?

Thanks so much!

[Tom Greenleaf]

Greetings. How much do you want to invest in this? New the layout was a failure IMO (about this year called a Vanagon) I recall. Everything was R-12 for vehicles.
Lots of questions on what you said in altering layout, compressor IDK what Subaru chose for ability probably not just one over models and model years.

One compressor if kept belt driven on engine IDK why there was a hint here to have another?
These would need just two ports what is has now I would strongly guess under the floor pan to front condenser strong electric fan(s) did vacuum and charge one all pressures right it was overwhelmed by interior size and distances just too long but was adequate if not too hot out or too much sun.

Other issue is most refrigerants are scheduled to expire sale or new product made known real useful in mobile A/C.

?> Doesn't this hardtop roof go up when parked?

Nice for a camper is harder for A/C as I be hunting around to a roof-top something at the cost of clearance for it.

I'll default to current day RV places for what is being done now and new up to plug i this to 110 where you go if seriously going all over in this.

Changes happening so fast hard to have a crystal ball to see what's next or maybe not so invasive on a motor vehicle such as refrigerated trailers (tractor trailers) huge inside.

IDK how bet/guess is 110 powered again IDK if from trailer or only Semi trucks equipped for that.

Another here Cornbinder likely to know how or what is done.

Refresh This was inadequate new stumped by layout of that as a vehicle,

[Cornbinder89]

This is something I know a fair bit about.
Heavy trucks with sleepers run a split system with two evaporators on one compressor. So it can work, but it takes a lot of engineering to get it to work well.
Two Tx valves work best rather than a Tx and orifice tube and Tx Two orifice tubes will not work.
You need enough storage in the receiver so that when only one evaporator is in use and the heat load is light, that the excess refrigerant can be stored, and the system still have enough to meet the needs of both evaporators running flat out with high heat load.
In trucks, the controls are set up with one being the "master" (front controls by the driver) and the other being the Aux (sleeper)
One problem you are going to face is there is a large area to cool, and getting the air distribution so that the cooling is even is going to be hard. Another is heat load from the windows, they allow a lot of heat in and are poor insulator.
Truck sleepers often have fiberglass bats just like a house, to insulate the walls and roof. I don't know how well insulated the VW is, but that would be the 1st thing that needs to be addressed.
So you start with two stand alone evaporators with Tx valves the Aux will also need a solenoid valve to stop refrigerant flow through it when the blower is not in use.
Generally, one frost switch is used to control the compressor and prevent frosting of the front (main) evaporator.
With two evaporators and Tx valves, the std sizes, being 1.5 or 2 ton, you need to size the condenser for 3-4 ton to get the best out of the system. This may require a remote roof mount condenser, as space in front of the radiator is limited.
Lines from the compressor to the condenser and return are going to be long, to minimize pressure drop hard lines should be used where you can and hose where movement is present.
Insulate the suction lines to keep the return from getting warmer than needed.
Lastly determining how much refrigerant is VERY HARD. When I build a custom system, I have looked for guidance on how to determine what the charge should be. I can find no formula, there may be one taught in engineering courses but I have found none in books. Trial and error was the only method I found. A receiver with sight glass is helpful here.
It will take a lot of work, but can be done.

[Cornbinder89]

You mention the problem with the dealer installed system not cooling evenly, This is going to be your challenge also. It doesn't matter how many evaporators you have if the air flow doesn't distribute the air evenly. The problem isn't the evaporator but the air movement. You will have to solve this problem. It may take ducting or circulating vans elsewhere in the van to keep it mixed.
Red Dot makes "packaged:" units for custom installs. A/C only or heat and A/C together. They have the Tx valve and solenoid valve as well as the blower. Many truck sleeper use these unit.
I don't know the spec's of the compressor you have off the top of my head, but it will need to be large enough to handle the capacity of the system you intend to build, Also you need to look at compressor speed at idle if you intend to idle for long time and cool the van. Compressor capacity is partly a function of compressor speed. There are some high capacity automotive compressors made. The GM A-6 is good for something like 44,000 BTU!
As far as safety controls, only one set is needed. Trinay is the simplest (mounted on the receiver or liquid line from the condenser) but you can go better since you are building your own. Elsewhere on this site I posted a low pressure switch safety that is much more responsive to low refrigerant charge than a trinary. and when combined with a binary (high/low pressure cut off) is very good at disabling the system long before damage is done.

https://forum.aircondition.com/forum/reference-and-resources/2751-tx-valve-a-c-compressor-safety-circuits

[Tom Greenleaf]

Thanks CB for coming by this one. OP + CB, Just BTW I don't know anyone who has a more comprehensive understanding on how and what could work.

All yours I'll try to watch and learn what comes of this,

[Cornbinder89]

Another thing to consider. All factory systems have a provision to bring in and cool outside air. This makes them far better than aftermarket that just keep recycling the air in the cabin. I would want at least one of the evaporators to have the ability to pull air in from outside.
As far as vintage air or others, I have no experience to recommend them or not. I had one car with a "hang on unit" back in the day and can't recommend them.
If you have a heavy truck junkyard somewhere about, older "pre 2000's" trucks tended to have packaged HVAC systems that can be removed and used. Sleepers had units under the bunk. I would look for truck in the 80's and early 90's to source from. Parts are readily available, and they are of the size you'll need.
IHC's from the late 70's onward had the HVAC unit under the passenger seat, and is mounted through the floor. It has a 1.5 ton AC and large heater with two blower motors. It has ducting for air in and out.
As I mentioned above many sleepers from the vintage I mentioned have Red Dot sleeper units of a fair capacity with blower and valves. You'd need to add switches or take the control panel from the sleeper also.
With something like a van, you are going to need more than just blowing air out from under the rear seat and dash board. Heat rises and cool sinks, the air in the van will be stratified, hot near the roof and cool at your ankles.
Ducting with outlets near the roof and return drawn near the floor will help make the temp more even in the van.
If you look at modern passenger vans, they have vents near the roof for the rear A/C and they run the length of the van. That is what you will need to duplicate to get even cooling, or something close to it.

[Cornbinder89]

If the OP'er ever comes back. I can get some pictures of the sleeper units, I have two in sleepers. I might also have a IHC underseat unit (in parts) to photo if he is interested.

[Tom Greenleaf]

CB + OP: So this vehicle is understood with the wild limits near impossible then, this is IMO why is obvious when you see the layout of it.
Air cooled "flat 4" engine in rear, belts point rearward under a hatch. That is for belt driven items no room to alter without totally changing this thing.
Even the heat was lousy never mind defogging windshield. Ducts had to be from rear I think using exhaust heat?

Can't know for sure if VW just suggested an aftermarket anything or not I'd say they did by 1986.
A/C would be belt driven off running engine so of no use if camping in it! It's not safe exhaust is out back.

Incredible neat designs made a light vehicle as much space inside it ignoring room for anything else. This should have a pop up top probably canvas can stand up inside.

Noted it has non-working A/C now I'd keep that and fix that it's already there in place.

IDK but think almost all wouldn't have A/C new or aftermarket if seriously needed perhaps Summer where it exceed 100F full sun, no shade.

If the objective is camping and using that was and travel just do without.

Neat thing, efficient but if "creature features " are a must it's simply the wrong vehicle to begin with.

My thought for this is what is the objective? Camping or while driving it?

[Gerrbear]

Thanks for your help! First I will try to answer your questions:

• I am hoping this will cost $1500-2500, but I would spend up to $4000 if needed.
• The stock Subaru compressor is a Zexel DKV-14G. the full nameplate says: Zexel DKV-14G, 404220-0542, U0920586092,ZXL 200 PG 150 cm³
• I would like to keep it to just one belt-driven compressor, I could use a bigger one if necessary.
• I would like the system to be designed for R134a or RedTek
• Yes, the roof goes up to access the upper bed. That won’t matter for the AC system, though, as I won’t be running the AC while the top is up.
• I won’t be installing a rooftop or other 110V system, just the belt-driven system for driving.

And now a summary of what I have learned from you so far:

• Two TX Valves will be used
• A large enough receiver/drier is required to store excess refrigerant
• Air distribution needs to be addressed
• Van needs to be insulated
• 3-4 Ton condenser is required
• Use hard lines where possible
• Insulate suction lines
• Refrigerant charge amount will be determined by trial and error, a sight glass on the receiver will help

Some more questions:

• The area in front of the radiator will fit a 16x24” parallel flow condenser. How do I determine the tonnage of that?
• Can I use any two evap/blower units, or do they need to be sized together for compatibility?
• If I install two solenoid valves, one for each side of the tee after the receiver/drier, will that allow either system to be on or off, or will I always need to run the front (main) system if I want the rear (aux) system on?
• I have read on VW forums that RedTek is better than R134a in terms of cooling capacity. Would you recommend RedTek or R134a?

And some additional info:

• The AC system is meant for use while driving, or maybe while idling for a quick cool down, but it is not planned for use while camping or parked.
• The windows are all tinted and curtained, and the walls and floor are insulated, though I might replace the insulation with some rigid foam board as it has better R value.
• I will be installing ducting and vents at head level and floor level at the back seat (there is no middle seat, so I will only be adding a pair of floor vents and a pair of wall vents). The front will keep the stock vents, at floor level and in the dash (as well as the defrost vents).
• I have attached a preliminary schematic for what I think you described, please let me know if it matches what you were thinking.
• Some people have installed a condenser under the floor of the van, and that seems to work with proper shielding from rocks, etc.
• The area under the rear seat, where I will be installing the rear evap/blower, is huge. Like 4’x2’x2’. I would love to have as much space for storage as possible, but I would rather have good AC.
• Dodge Caravans and Chevy Suburbans use dual AC like I want. Their systems won’t fit under my dash, though.

Thanks again for all your help! Your expertise and willingness to share are hugely appreciated.

[Cornbinder89]

Who ever is selling you the condenser should be able to tell you the rated BTU for it. I don't think 16x24 is going to be anywhere near what you need for a dual system.
The reason people say R134a isn't as good as R12, is mostly it takes more surface area in the condenser to shed the heat. If you put 134a in a system built for R 12 it will give poorer performance, If however you use it in a system sized for 134a it will equal the performance.
I would oversize my truck condensers when switching to R 134a and found it more than up to the task, even with the rest of the system being designed for R 12.
From what I remember from my brothers Westphalia there will not be room in front of the radiator for as large a condenser as you will require. IIRC there is a "luggage rack" type thing molded into the roof over the driver. and this part of the roof doesn't go up with the "pop-up" rear section. A perfect place to mount a large . roof mount condenser/fan package.
As for prices, I wouldn't start to make a guess of what it is going to cost.
In all likelihood you aren't going to get it right in one go. If you try to skimp, you may find it cost more than going big in the beginning.
On my cabover semi's I fitted a 31,000 BTU condenser that was aprox 29"x 20" on a 2 ton system. It cooled great, even cycling the compressor off on 95 deg days! running R134a The rest of the system was stock for R12. I'd say the minimum you would want for a dual 1.5 ton evaporators and even then you are skimping. 32,000 to 45,000 BTU condenser would be better. Anything in that size is going to be roof mount only.
If you want to be able to run only rear, only front or both together, you are going to need frost control in both evaporators and solenoid valves on each if you are using frost switches, but if I were going to build the system for that type I would use a form of evaporator pressure regulator control on the outlet of each evaporator. That will keep each evaporator at the frost point regardless of what load the other evaporator faces, and keeps the compressor running all the time.
I suspect that OEM compressor may be a little or a lot too small displacement for a dual system, I can't find spec's for it on line.
P.S I once tried to build a system that used two different power sources, two compressors and condensers on one evaporator. I made many changes from original design, and I got it to work, but not as well as I wanted it too. Lots of time and money, some wasted over the course of the project. I wanted one power source to run it while driving and another while parked/sleeping. Then the work I was doing and where I was traveling changed, and I found I didn't need A/C while parked very often anymore and I could no longer afford the weight of the separate diesel engine to power everything, so I pulled the system out. I just used a separate diesel heater for warmth, and idled the big engine the very few nights I needed A/C all night.
All it takes is time, money and the will to do it over again until it works!

[Cornbinder89]

WD_2021 (cld.bz)
page 24 has the sleeper unit I run in a few of my trucks
roof top condensers start on page 82.

[Tom Greenleaf]

I'll try to be concise meant to help and calculate possible/realistic BTUs needed.
I'm from MA pretty much lifelong wasn't so congested only some wild heat and stopped traffic also over dark asphalt. It isn't that hot unless trapped like that so once knew of many buying new order A/C delete options just save the aggravation cost nasty also impaired doing routine things vehicles need.

Pretty much I can still live like that no need for mobile vehicle but that's all there is out there and for a while shape, lack of air for passengers via vents powered or not adequate for most.

Vehicle makers will eliminate what you don't notice quick so gone are real outside air vent powered or passive.

Late 60s into early 70s vehicle meant for passenger were required to change air inside so often with fresh, release the already cooled or heated air renders insulating marginal - situation by situation.

Just know that is vehicle's OE specs meant you lose all interior air so are re-cooling or heating new mostly those that say or icon for recirculate just reduce it to the standard exchange.

That has to wildly matter - think about that. This model year throw in some "camper" separate rules for those it might not you can look at door jams many are clearly there. Not discussed much out there or IDK what the web has to offer on that.

Point is factor that loss when calculating BTUs required,

[Gerrbear]

A few clarifications:
- This van was not and is not air cooled. The engines water cooled after 1982. As such, it uses a a normal heater core in the front fed by coolant lines running back to front from the engine to the radiator, with tees going to/from the heater core. The air cooled vans probably had terrible heat, but I have no experience with them.
- My van does not have any kind of AC, and it never did. The AC systems I was talking about were options that other vans had, but mine never did.
- I don't know what fraction of these vans had AC, but it seems fairly common, but having dual-zone is very rare and required giving up the glove box, which I don't want to do. Many people who still have the stock engines removed their AC systems as they weren't great and the van was underpowered enough already. My engine is roughly twice the HP/Torque of the stock engine, so I have some room to work.
- I want to use the AC for driving, not for camping.
- The van does have a ram air intake for fresh air to circulate into the cabin. It comes in at the front and then can be directed to dash vents and/or through ducts to vents in the back. I am planning on adding a flapper valve to that intake so I can choose fresh or recirculated air. There is a spot in the back I could use for rear fresh air (was for a gasoline furnace which I removed), but I was planning on blocking it off and having the rear as recirculated air-only.

As for AC capacity, I've spent some time on VW forums and I don't think it will take as much as it seems. The stock AC was cold enough to freeze out the rear passengers and keep the front ones cool, the problem wasn't capacity, it was air distribution. And for the dual zone systems, they were plenty cold and ran both systems off the stock compressor and condenser, and apparently the condensers back then were inefficient tube and fin designs, so a new parallel flow one that is the same size should be adequate. With that being said, I am going to do my first design with the stock Subaru compressor and a 16x24 rad-mounted condenser. I already have the compressor and the condenser is cheap, so if they are inadequate I won't feel too bad replacing them.

You are right that the luggage rack would be a great spot for a roof-mounted condenser, I will keep that in mind if the front-mounted one proves inadequate. I am pretty resigned to the fact that this will be a trial and error kind of process, and I don't expect it all to go right on my first iteration.

The only problem then is overall system design (please let me know if the fluid schematic above makes sense), wiring (I will be doing up a wiring schematic once I am happy with the fluid schematic), and evap/blower selection. After that I can start buying parts and figuring out fluid charge amount, accumulator sizing,

Thanks both of you for all your time and thoughts on this. I looked at the Red Dot Catalog and it looks good. My challenge now is to find the most BTUs I can find in a package that fits where I want it to go.

Questions:
- "you are going to need frost control in both evaporators and solenoid valves on each if you are using frost switches, but if I were going to build the system for that type I would use a form of evaporator pressure regulator control on the outlet of each evaporator. That will keep each evaporator at the frost point regardless of what load the other evaporator faces, and keeps the compressor running all the time." Do you have any info on what that might look like/where I could source it? I have no idea what that would be.
- Can I use any two evap/blower units, or do they need to be sized together for compatibility?

Thanks again!

[Cornbinder89]

Evaporators do not have to be the same size, the job of the Tx valve is there to meter the refrigerant for the needs of the evaporator.
I am aware of the liquid cool vans, my brother had one.
I don't have any book that shows a "16x24" the closest I have in my book is 14x 25 3/4 x 1 2/16 is 18,000 or 1 1/2 ton, enough condenser for one evaporator, most are either 1.5 ton or 2 ton. If the unit doesn't list a BTU or ton value ask, or look at the Tx valve.
Undersizing the condenser, and you be say "134a doesn't work" when it is the condenser size that is the problem.
The Red Dot unit I referenced was just over 1.5 ton, so if you are useing two, you need to shed 3 tons of heat 36,000 BTU.
If one unit will cool the van, then put your money in distributing the cool air, not adding another evaporator. If it will not, then use two and size the components to match.

[Cornbinder89]

Let me try and explain it another way:
If you have a 1.5 ton sized evaporator, Tx valve and condenser with a compressor that can keep up, the system will be at its best. A Tx valve controls the refrigerant in the evaporator such that it all just boils of to vapor by the outlet. It doesn't care what the evaporator temp is, only that the temp at outlet of the evaporator is close to the temp at the outlet of the Tx valve.
So, why are there "ton rateings" on the valve. The valve is never fully "closed or open" it is a variable orifice that either opens to allow more or closes to allow less. If you put too big a valve on a smaller evaporator it will have trouble regulating the flow, Like putting too big a carburetor on a small engine, it will work just not very well.
Evaporators are sized to the amount of heat they can absorb under standard conditions. a 1.5 ton can take 18000 BTU.
Match the Tx to the evaporator, and you have a good functioning "cold end" of things.
If the cold end is where heat is put into the system, the condenser is where it is removed.
Unlike the evaporator there isn't a "valve" on the condenser. If you put a 1.5 ton cold end on a condenser that can only handle 12,000 BTU you have a system that can only handle 12,000 btu, BUT if you put more BTU in at the cold end, the excess heat stays in the system and gets cycled back to the evaporator and it continues to build. You get high head pressures and very poor cooling.
As long as the outside temps are mild and the inside isn't too hot, it will function ok, until it reaches the limit of the condenser. As heat load rises the performance gets worse and worse.
Condensers built for R12 would be good enough with the old "tube and fin" because the R12 molecule was bigger than the R134a. It is why R134a does best with the extruded aluminum "parallel flow" design.
If you put that 16 x24 which I would guess is about 1.5 ton, you will only get 1.5 ton worth of cooling, or about one evaporators worth. Using it on two evaporators will not increase the cooling, but decrease it, giving mediocre cooling blowing from two places.
You;d be better installing one evaporator and put your money into ducting where it needs to go, rather than 2 units on a condenser that can only handle one.
You can't absorb more heat if you don't get rid of what the system already has.
Each component of the whole system must be matched to everything else to get the most out of the system.
I mentioned before you might get away with 31,000 BTU condenser on two 1.5 ton units. You will not get 3 ton, only 2.5 ton out of the system, and if the heat load is higher than that you will see high head pressure and load on the compressor. Chances are 2.5 ton would be more than enough under most conditions, but you have paid for more of a system than you are getting, and putting extra heat and load into the compressor.
Compressors are cooled by the returning refrigerant and refrigerant oil that comes back from the evaporators. It will be near 32 if all is working as it should. The less cooling the hotter the compressor runs for two reasons. First the condensing pressure is higher and 2nd the cooling from the return is less. Slipping belts and clutches and high pressure shut down are all in the mix.
On my trucks, the difference between a condenser that was "just big enough" and one that was oversized by about 24% was about $25. The results can not be monetized so easily, but head pressures in the low to mid 100's when air temps are in the 90's make a big difference, even on 110 deg days the pressure ddn't spike to turn on the fan unless stopped or slowly moving.
So, to sum up: If one 1.5 ton unit will cool the space if the air is distributed, then use one and add booster blowers and ductwork to get the air where it needs to be. If 1.5 ton will not cool enough add a second unit or a bigger single unit, but MATCH the condenser to fit the unit, not the space you have in front of the radiator! If you only have space for a 1.5 ton condenser, either stick to that size unit or move the condenser to where you can have a big enough one. .

[Gerrbear]

Thanks for that. I see your point now. Would a condenser under the van work? I have seen that done before, and I would prefer that as I use the luggage rack pretty often. If not, I will look into a single evap/blower system with ducting/fans for distribution.

Question about air distribution: If I was to have the evap in the back, under the rear seat (where there's lots of room), do you think a fan in the back, pushing the cold air into ducts that run to the front of the van (maybe under the floor) would be adequate, or would I need a fan in the back pushing and another fan in the front pulling?

Thanks again, I'd clearly have no chance of success on my own.

[Cornbinder89]

To be honest, I don't know. If you have a factory heater and blower under the dash, There might be a way to unitize that as you "booster" blower, and would allow for use of the existing air ducts.
Booster blowers are a lot cheaper even if you had to buy one new, then another evap.
The advantage of evap under the rear seat, is the return lines are short, which is good, and you can leave the stock heater under the dash if so equipped.
Even if you end up needing a 2nd evap, if you start with one under the rear, you can decide what you are willing to give up in the front if you need too.
The only draw back of the rear evaporator is: It most likely wouldn't draw outside air, but only inside.
As far as where to place the condenser, anywhere with less the ideal air flow to it will reduce its capacity. It is why in the early years of truck A/C roof mounts were common, it is the ideal place to put a condenser, it gets plenty of ram air and doesn't get hot air just above the pavement. Air that comes a few feet above a black surface can be heated far above what open air is.
Behind the grill is not ideal, but is a compromise. It is cheaper to place where one fan can cool both it and the radiator, and air flow has already been analyzed.
Placeing the condenser under the van would be a bad idea from many angles. 1st the risk of damage, 2nd it wouldn't be 90 deg to air flow, so air flow would be a problem and 3rd the above about heat off the pavement.
Air ducts under the floor are ok but you want to insulate them so they don't absorb the road heat.
As I said, there is going to be a lot of experimenting to find what works best. I like the idea of one evaporator in the back, then add on to that to try and find what works. An add on blower (push from the back, draw from the front) IE rear blower into the suction of front blower) with some sort of flow divider to supply the rear seat passengers.
Espar and Webasto sell a lot of ducting supplies, Y's and control doors that might work well. Look on E bay for ideas..

[Gerrbear]

Awesome, thanks. I've been talking with suppliers and others and I think I've got enough to get started now, so I'm going to start ordering parts. Thanks for your help. I'll post some updates as I go.

I'm going to start with a rad mounted condenser that others have used with success on dual Evap systems, and run two evap systems (not sure which ones yet, still talking to suppliers).

I could easily add a fresh air intake to the rear system (I will have one in the front to improve my defrost) as there is an intake for the (now removed) furnace. I would have to add a cabin filter to it though, as it would pull air in from above the rear wheels and it would be really dusty without it. Is it worth it, you think?