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New R12 AC system in Dodge D150 blowing relief valve - lack of condenser airflow?

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  • #31
    Originally posted by Cornbinder89 View Post
    If your up for a gamble, keep adding a little at a time until you reach 30 to 32 psi low side with the engine running 1000-1500 RPM. Keep and eye on the high side as well, it will likely rise with the low side, but not very fast, if the high side starts riseing quickly stop and suck a bit back out. Go slow and allow the system to stabilize before adding more
    Your 60 deg vent temp suggests that all refrigerant is boiling to gas long before the outlet of the evaporator.
    Inlet and outlet temp of the condenser is a many factored thing. If there isn't much heat put into the refrigerant at the evaporator either because its cool or because there isn't enough refrigerant in liquid form to absorb heat and expand into gas, the amount of heat in the system will be low and so will the high side temps and pressures.
    At 96 deg I would expect high side to be in the low 200's to mid 200's depending on how good the condenser is and how much airflow it has.
    It's very difficult for me to hold the idle up by hand by myself and also watch the gauges but maybe I can have my brother help me tonight.

    Boiling to gas long before the outlet of the evaporator - does this suggest significant undercharge at this point?

    You're right it's a bit of a gamble. Do I want to risk a decent amount of more R12 or just go ahead and start fresh with the new condenser/expansion valve/drier... hmmm.

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    • #32
      Yeah, it points to undercharge, but only if everything else in the system is working as it should. Another way to check is if you can get to both tubes from the evaporator on the evaporator side of the Tx valve. they should be close to the same temp, indicating that liquid hasn't all boiled to gas before the outlet. If the outlet (suction) tube is warmer keep adding a little at a time until both tubes are close to the same temp.
      In all cases you have to go slow and let the system "balance" before adding more, otherwise it is easy to over shoot the mark.

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      • #33
        Well... I replaced the expansion valve and condenser and drier last night. Vacuumed and re-charged - factory charge calls for 44 oz of R12 and I have about 41-42 oz in it at the moment. Sight glass is clear.

        It was 91 degrees ambient temp and 47% humidity when I got it finished. Of course, this was 8 PM at night so it wasn't near as hot as it could have been despite the ambient temp.

        At idle, it was giving me about 30 PSI on the low side and 230 on the high side. Still doesn't cycle at idle but does cycle properly if I hold the gas up above 1200-1300 RPM or so.

        Center vent temps last night were about 55 degrees. Certainly not "cold", but adequate, I guess. My concern is that in the heat of the day it won't be able to do that and will just hover above 60 degrees.

        I came into work today to catch up and drove it this morning. It's "only" 87 right now and 56% humidity and the center vent was doing about 58 degrees. Unfortunately all signs are pointing to 60+ degree vent temps during the heat of the day.

        Pretty frustrating. Does anybody have an R12 pressure/temp chart as far as operating pressures? For some reason I can't seem to find one online any longer. Are the 30/230 pressures normal now?

        Wonder if I should add a few more oz of refrigerant but I can't imagine that substantially improving the vent temps given that the sight glass is already clear.

        Also, Cornbinder - the expansion valve is mated directly to the evaporator right at the firewall, so I don't really have a way to get to the tubes on the evap side of the expansion valve, unfortunately.

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        • #34
          chart is here:
          https://forum.aircondition.com/forum...pressure-chart

          I'd feel better about the pressures if they were at 1500 not idle. We still don't have a 1500 pressure reading. 230is a whole lot better then 400+ blowing the relief.
          Last edited by Cornbinder89; 07-14-2018, 11:27 AM.

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          • #35
            Originally posted by Cornbinder89 View Post
            chart is here:
            https://forum.aircondition.com/forum...pressure-chart

            I'd feel better about the pressures if they were at 1500 not idle. We still don't have a 1500 pressure reading. 230is a whole lot better then 400+ blowing the relief.
            I did see that chart but I meant something more along the lines of this, but for R12:

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            • #36
              The type of chart you posted really don't have much meaning. They are approximations of what you MIGHT expect to see. The chart I posted is what the phase change temps are for the two refrigerants at giving pressures, or for a given temp what the phase change pressure will be. . Why they are, what they are for a given system is up to the mechanic to sort out. I don't put much faith the charts that try and tell you what the pressures should be at a given temp and humidity, there are just too many variables.

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              • #37
                I had a problem that just about had me throwing in the towel. The new condensers I was getting were being painted (powder coat they said) without the sealing caps in place.
                Paint was getting inside the condenser when manufactured!. They then carefully sealed them and sold them to me. When I installed them, the paint was carried thru the system plugging up the OT. Within a few days, it failed. I finally figured it out when upon a disassembly, I noticed that my condenser O ring was silver (paint color) instead of green.
                I had a brand new condenser still sealed in the box, from a different supplier, but it turned out to be from the same manufacturer.... I uncapped it, and swabed the inside of the tubes with a Q tip.... A LOT of silver paint came out.
                Needless to say, I had a serious conversation with the vendor. They checked their stock, confirmed my findings and were happy to refund my money.

                Since my old truck condenser was pretty much unavailable now (That was the only manufacturer) I went with a universal condenser. It was quite a bit cheaper than the tube and fins I had been getting. Had to make custom hoses though, so it ended up being about the same cost. That has been working great for 14 months now.

                Just throwing this out as a possibility. I know a factory was doing this, and they were making ones for older trucks. Not sure what the effect would be on a non OT system, but it could not be good
                Last edited by huntindog; 07-14-2018, 11:51 PM.

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                • #38
                  So, yesterday my brother and I went around hunting for some parts at a couple of junkyards. I actually found a good non-cracked front windshield for the truck as well as FINALLY scored some door lock caps after a year of hunting, so that was a nice find but dang it was 100 degrees all day so this was a real good test of the performance being out and about in it.

                  Truck blew 60-62 degree air the entire time out of the center vent. I must that say that it did keep us "comfortable" in the 100 degree weather but man if I could somehow wrestle just 5 or even 10 more degrees colder out of it it would make a world of difference. It's kind of weird that it just seems to peg at 60 and refuses to get any cooler. It almost makes me think there's GOT to be some sort of blend issue or outside air getting in or something.


                  huntindog - I do specifically remember seeing the sealing cap areas on both condensers and they were clean. In fact, the entire "face" of the panel deal was completely clean/paint free.



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                  • #39
                    I wouldn't be happy with those temps either. Not sure where I would go from here. I am also at a loss to explain why less the 6 oz less than before would make the high side drop from around 400 to low to mid 200's?
                    Given all you've replaced, and some of it twice, I can't advise anything you haven't tried.

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                    • #40
                      Originally posted by james89dx View Post
                      So, yesterday my brother and I went around hunting for some parts at a couple of junkyards. I actually found a good non-cracked front windshield for the truck as well as FINALLY scored some door lock caps after a year of hunting, so that was a nice find but dang it was 100 degrees all day so this was a real good test of the performance being out and about in it.

                      Truck blew 60-62 degree air the entire time out of the center vent. I must that say that it did keep us "comfortable" in the 100 degree weather but man if I could somehow wrestle just 5 or even 10 more degrees colder out of it it would make a world of difference. It's kind of weird that it just seems to peg at 60 and refuses to get any cooler. It almost makes me think there's GOT to be some sort of blend issue or outside air getting in or something.


                      huntindog - I do specifically remember seeing the sealing cap areas on both condensers and they were clean. In fact, the entire "face" of the panel deal was completely clean/paint free.


                      I much prefer unpainted condensers now... Really no reason to paint them. As for mine,,,,,sealing caps were in place, and everything looked good from the outside. They used silver paint, which was the color of the unpainted aluminum..... The test was removing the sealing caps, and inserting a Q tip.... Paint came out of the inside.

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                      • #41
                        Okay, so, I was able to make a video last night of the pressures as I held the throttle cables to keep revved up. No clue what the actual RPM was as I don’t have a tach, but clearly the high side pressure is still far too high at actual operating pressures even though it’s better than it was and no longer blows the relief valve. I was also able to verify that the fresh air vent flap is sealing very firmly against the side of the truck down there in the passenger footwell area. This was 101 degrees ambient temp, around 30% humidity, but 8 PM at night so it didn't "feel" like a hundred degree day would in the middle of day with sun overhead.

                        https://www.youtube.com/watch?v=B83mBO9nPuo&t=1s

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                        • #42
                          Yeah the high speed high side pressure is higher than I think it should be.
                          Just thinking "off the wall" I wonder if there is some sort of restriction in the evaporator, or something like that. that is reducing flow and preventing the Tx from doing its job? I know I'm "reaching" here but I have very little to recommend. Either up the condenser capacity to try and get the high side down, or look for internal problems in the evaporator.
                          The 1st suggestion I admit, is treating the symptom and not getting to the route of the problem, but may help.

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                          • #43
                            Originally posted by Cornbinder89 View Post
                            Yeah the high speed high side pressure is higher than I think it should be.
                            Just thinking "off the wall" I wonder if there is some sort of restriction in the evaporator, or something like that. that is reducing flow and preventing the Tx from doing its job? I know I'm "reaching" here but I have very little to recommend. Either up the condenser capacity to try and get the high side down, or look for internal problems in the evaporator.
                            The 1st suggestion I admit, is treating the symptom and not getting to the route of the problem, but may help.
                            I think you're right in there's gotta be a restriction somewhere. The problem is how exactly do I find/fix it barring just replacing all the parts and doing the job yet again. Sigh.

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                            • #44
                              You did put a new evaporator in didn't you? did you save the old one?

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                              • #45
                                Originally posted by Cornbinder89 View Post
                                You did put a new evaporator in didn't you? did you save the old one?
                                Yes the evaporator is new. I do have the old one still yes.

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