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Auto AC problem

Let me throw in my 2¢ worth.

I do a lot of A/C repair, including having to recharge my '96 minivan this year, and I'm inclined to think it is no overcharged, mainly by the 65 pound suction. I would be inclined to recover the charge, pull a deep vacuum, and WEIGH in a fresh charge of R-134a. Then see how it works, before putting all the extra work into it.

As far as the TEV and Accumulator, that would be the next logical step. I've read that many car A/C systems have a drier in the accululator, which would then warrant changin it out when the system is opened up.


  • Auto AC no workie

    Prof. Eugene,

    I hope this is not too off topic but, Dan says "there's nothing the Professor doesn't know about air conditioning and refrigeration"

    I've been having some MAJOR trouble with the AC system in my 95 Montero.

    I've checked and charged the system with 134A using a Quick Charge™ gauge/fill gizmo and about one small can of refrigerant from NAPA and the system seems to operate just fine until I take it down the road and the engine gets hot. The compressor will then intermittently shut off (clutch disengages) and cooling stops. I thought that it might have been a faulty hi/low limit switch so I tested the switch and found it was closed. Just for kicks I jumped it out and went for a drive. Same thing. The compressor still disengages. I've also checked the entire system for leaks with my HCFC detector as well as with Mr. Bubble™:-)

    Fed up with this intermittent problem, I took the thing to my mechanic and asked him to drive it around for a while and find out what the problem is. He told me that he believes that it's a "clogged expansion valve" because he was measuring in excess of 350 PSI on the high side and 65 PSI on the low. He's got to drop the dashboard on Tuesday disconnect the evaporator and change out the TEV. He also wants to change out the accumulator. Is this the right approach?

    I was thinking that there might be moisture in the system and ice clogging the orifice. If this is the case, wouldn't a good deep vacuum on the system do the trick? How would you know if it is ice/moisture or some other type of contamination clogging the orfice?

    Don't want to change out major parts without knowing for sure and it's getting DAMNED HOT out their.


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  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    Sounds like an overcharge

    Here we go Gary! You get he award for the first question answered by the "professor!"

    Sounds like a system overcharge. Here's the deal. On an 85 degree day the head (high side) pressure on the system should be about 159 psig. Although you mentioned that the high side pressure was about 350 psig, the outside ambient temperature would have to be in the range of 200 degrees. So, it is safe to say that the head pressure is definitely way too high. In addition, the low side pressure should be in the range of 22 psig, which equates to a 25 degree evaporator saturation temperature. (Automobile air conditioning systems operate as medium temperature refrigeration systems). The 65 psig low side (back) pressure indicates an overcharge as well.

    If the metering device was indeed clogged, the high side pressure would be high but the low side pressure would be lower than normal, not higher. For this reason, I am incline to doubt that the metering device is bocked.

    in order to determine if there is moisture in the system, turn the air conditioninc system off and allow it to sit for half an hour. Take a pressure reading in the system and compare the saturation temperature (the temperature that corresponds to the pressure in the system) to the actual outside ambient temperature. If these two pressures are the same, there is no moisture in the sytem. If the saturation temperature in the system is higher than the actual outside ambient temperature (more than 3 or so degrees), there is moisture in the system.

    Here's an example:

    Saturation pressure of the system after resting: 95 psig

    From a pressure/temperature chart, the saturation temperature for this pressure is 85 degrees

    Actual outside ambient temperature: 85 degrees

    Conclusion: No moisture in the system since the two temperatures are equal.

    If moisture is present, be sure to properly recover the refrigerant, evacuate the system and weigh in the proper charge.

    Hope this helps, Gary
  • Kal RowKal Row Member Posts: 1,518
    if there is air in the system...

    (common in auto units that leak) then you will get those double high readings too - get it recoverd, evacuated and charged by weight - or you will never know
  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    Air in the system

    The purpose of the low pressure switch (control) on the system is to disable the compressor in the event the low side pressure falls below a predetermined setpoint, which is above atmospheric pressure. Even if the system leaks, air (and moisture) should not be introduced to the system, since the low pressure switch will open and release the compressor clutch. If however, the low pressure switch has been jumped out (a big no-no), the compressor will continue to operate and yes, under these conditions, air and moisture will be pulled into the system.
  • AWARD?

    This helps so much. Seems too many people are "parts changers" instead of finding the real problem.

    I'll let you know how this turns out. Thank you for your detailed response. I'm so happy to have an AC guy on board at this site.

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  • EUDE \"Huge help\"

    I think we need a nick name for you. I would suggest: EUGE meaning huge. Please excuse my candor but, I just got my car back and the bill and it stings a bit.

    The bill is as follows;

    Replace expansion valve and receiver/drier. Evacuate and recharge.
    Parts $179.00
    EPA 1.00
    Shop 3.00
    labor 269.50
    Freon R134A 28.50
    plus tax

    Here's the thing. It works GREAT now but,,, I told him that there was a small leal on the sight glass of the reciever. The receiver was changed out but,,, the TOP portion includes the sight glass and all associated fittings. He said "(I TRUST THIS GUY) " he couldn't fond a leak anywhere around the top of the receiver.

    got home and used my friend MR. BUBBLE™ and the O-ring/seal around the sight glass STILL has a very small leak.

    What should I do?

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  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    Here's the Deal

    If you, with the aid of Mr. Bubble, know for a fact that there is still a small leak in the system there are a couple of facts you should definitely be aware of.

    The first and most obvious is that at some point in the future you will be short of refrigerant again and will have to add R-134a to the system. This is definitely not a good thing especialy since you just paid good money (is there any other kind) to have it fixed right.

    The second issue is a major one. If the technician put the system on a vacuum pump to evacuate the system, there is no way that the vacuum held for any length of time given the fact that you were able to locate the leak relatively quickly on your own. Improper evacuation can lead to a number of system problems.

    The third and most important issue is this. You now have air and moisture in your system. Since the system was put on a vacum pump, the pressure in the system was reduced to a pressure below atmospheric. Since high pressure goes to low pressure, air and moisture are pulled into the system. Moisture in refrigeration systems allow acid to form within the system. As we all know, acid in a refrigeration system is not a good thing.

    If I were you, I would pay another visit to my mechanic, making certain to bring along a bottle of Mr. Bubble. Point out the location of the leak and demand, in the nicest way possible, that you want the system re-repaired.

    This is the important part:

    Make it clear that the refrigerant that is presently in your system is contaminated and that you want that refrigerant recovered and replaced with VIRGIN refrigerant. Also, just to keep the pressure on, ask for all old components that were removed from your system. I can almost guarantee that there was absolutely nothing wrong with the metering device, for reasons mentioned in an earlier post.
  • prof.

    "There is no way that the vacuum held for any length of time"? Hmmmmm?

    The refrigerant that is presently in my system is "contaminated" because I know of a very small leak that was missed by my mechanic and I should have the refrigerant recovered and replaced with VIRGIN refrigerant? He MUST have "pulled" air into the system when he used his vacuum. As I understand his regular regiem, he has a "Machine that tells him everything". His words.

    WOW!!! I'm really upset now. AC works now:-) How long?

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This discussion has been closed.


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