Tried just about everything

[Stevc C]

Hi all,
I have a 1994 Mitsubishi Delica and the air con runs at around 8-10 degrees at idle, but cools to 5 degrees when the engine is at 2000rpm. It always gets "cool" but not cold at idle. So on a hot day its useless.
It has had new Tx valves, new compressor, new dryer, a system flush and a second compressor just in case the first new one was a dud. I also put in new electric fans on the condenser and checked their operation. The engine fan is working fine. I have also tried spraying water onto the condenser at idle with no effect on the air con performance. The only thing that changes the temp is RPM up at 2000. Have driven it at low speed and high revs - air con stays cold. Have driven at low speed in high gear and it warms up. Have driven it at high speed in high gear - air con warms up. Have driven it at high speed in low gear and it cools down. So, air flow does not seem to be the answer.
The gauge pressures read just fine while the engine is cold, but as it warms up the high side goes high and stays there.
This vehicle has front and rear cooling with a switch to go front only or rear only or front and rear. At idle it cools at 10 degrees with both on and 8 with either one on separately. That means there are two Tx valves. Both have been replaced.
Also, on start up the system takes a long time to pull down to 10 degrees.

So I have no more ideas as to why this sucker runs warm below 2000rpm.

Any thoughts appreciated.

[Cornbinder89]

I have a couple thoughts but no "ah ha" moments. Better cooling at higher speed suggests not enough compressor capacity at lower rpms. High pressure on the high side suggest poor heat rejection. That being said, the mist test should rule out a poor condenser. That leaves a possible over charge (too much refrigerant) in the system.
A Tx valve system stores the excess refrigerant in the receiver as high pressure liquid, if it is overcharged liquid will back up in the system and pressures will rise.
So I would recommend charging by weight with a known accurate scale. Too much oil could also reduce the heat transfer, so is something else to watch for.
As I said, no ah ha moment and an exact cause, but somethings to check.

[Tom Greenleaf]

Similar thoughts: Please use a C. or F. this is based in the US makes for converting temps. I couldn't have any first hand experience with this vehicle would probably not be sold to the US as you have it so basics are the rule.
Still some thoughts and trouble spots will end with last idea first already said:
* This has to be 134a for a model year 1994 hope you have original decal(s) for system's total capacity AND a way to vacuum and charge to exactly that amount. Full vacuum and refrigerant only.

Issues with this plus year 1994 both! Several vehicles just pre retrofitted an R-12 system for 134a no real changes except for type of rubber products used in components. Dual air adds to reasons for erratic pressures and output temps when you get there. Do know you are splitting the compressor's ability to different evaporators the BTU potential was not much different just released in two areas.

The "catchy" comment was poor at idle for all the reasons Cornbinder89 suggested. Know which type of condenser you have old type or newer high efficiency tell tale would be system capacity not like 85% of the model year before this one same set up. If far less it's the newer products. If so know those don't take abuse or debris well or at all rather act as a filter are expendable with prior failures may not be the listed charge known to it new adds complication and calculating a lot.

So it's still the same just begin with a known charge is known from empty if a calculation need I would need to know what was changed for only a wild guess. Know this though you can add too much and be the problem dealing with unknown amounts try like crazy NOT to pass that exact amount depending on equipment available most needed IMO can be a favorite of my own, infrared, touchless thermometers tells you what is happening where if expected or a problem spot,

[Stevc C]

Thanks for the replies....yes it is difficult to know where to go. Will check the charge..try a lower charge and see if it resolves. Oil should be okay as the system was flushed and then the correct oil amount put back in. Apologies re the C, F. regards.

[Tom Greenleaf]

It's just of interest how F. can match up to pressures when and where they should be vs C. I/we can't know what equipment you have to reduce charge by exact amounts takes costly equipment and measure how much comes totally out and again back in so I'll guess you are trial and error takes ages of experience and all observations all at the same seconds you are doing anything!

There are charts here of what to expect when doesn't say means proper airflow thru grille and at what RPM you are at. Also what the output of a front center vent is going to stabilize at - you are already supposed to know that stuff makes it its own profession or tech area of expertise.

Jut a tip to help when/if using pressures. Shut the rear off and work with just front on dual set ups. They don't share evenly can and will throw you off.

Add one more for now. If just venting out some refrigerant you don't have a clue where you are or how much came out. Takes time. Stop. Drive it around the block type thing and retest it. Why? Because sitting in one spot the area gets hot ground/surface you are on just with engine running.

The end answer is yes you can but OMG it's tricky and takes time and instantly know all temps where by the moment. I use in/out wired thermometers so I can see inside vent temps, incoming air temp, and infrared for hoses, condensers and at evaporator hoses at firewall all in nano seconds. It's still hard.

Good luck. If in doubt stay on low side of a charge not over is much harder to deal with plus know that's the most likely reason for poor performance,

[Tom Greenleaf]

Here's the chart in a link at this site > https://forum.aircondition.com/forum...pressure-chart <
Always something to add. You do avoid "too" cold and just FYI I find a temperature rise of about 4-5F from chart listed temp or what it should be at closest spot to firewall hoses goes up that much from heat off of engine thru firewall in dashboards/instrument panels stuff all around,

[Stevc C]

Thanks again, will show the chart of temps to my air con guy. He is checking that the Tx valve he installed has correct pressure rating. Getting desperate. Cheers

[Tom Greenleaf]

Charts are helpful if or when just that is unknown for sure. Then if not right you have the basepoint to work with. Good luck,

[Olds442]

How well does it cool when you drive at 60 to 70 mph ? Long shot, but is it possible your fans are wired backwards and are not pushing air over the condensor ?

[Cornbinder89]

He wrote that he had driven at high speed in high gear, it warmed, high speed in a lower gear, it cooled, that does not point to an air flow problem, but we have not heard back in awhile to know if he has had any progress.