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My ac is working backwards!! Please help!!

keigaro on Thu June 16, 2011 11:24 PM User is offlineView users profile

Year: 1988
Make: Nissan
Model: hardbody
Engine Size: 2.4
Refrigerant Type: r134

Well my husband and I oiled, vacuumed, and recharged the ac. It was cooling fine but notice there was a leak in a valve and all the refrigerant was leaking out, causing the ac to start to get warm. We discharged all the freon, replaced the valve, vacuumed it down again, and recharged again!! Now when the ac is turned on, it shows no pressure, when it is turned off, it shows 70psi on low side. My husband let some of the freon out of the high side and psi went from 0 to 30 and the ac started getting cold, but then it kept dropping as did the pressure. The pressure will drop for a few minutes then it will go normal for a few minutes. We cannot figure out what is wrong. We have run out of money, time and answers, so please give me some advice on what the problem could be. Even the inside air adjusts appropriately with the pressure, getting cold when normal and getting hot when no pressure.

mk378 on Fri June 17, 2011 7:34 AM User is offline

Sounds like a balky TXV. If it sticks closed the low side will drop to zero (or even below) and cooling will stop. The high side will stay about the same.

When converting, it's essential to replace the receiver drier. I think the ones that disintegrate inside (and clog the TXV with debris) when used with R-134a were mostly on older American cars but you could have one.

Edited: Fri June 17, 2011 at 7:37 AM by mk378

NickD on Fri June 17, 2011 10:35 AM User is offline

This system was R-12 and you are listing R-134a as the refrigerant. Number of steps have to be done, no sense in repeating those steps, in the FAQ section. Question is, are you converting and did you go through all these steps?

keigaro on Fri June 17, 2011 11:43 AM User is offlineView users profile

To start from the beginning, my grandfather used the truck to haul trash back and forth to the dump and didn't maintain it very well. I love my grandpa but he was doing some crazy things such as recycling oil, brakes, and tried fixing himself after he wrecked it. It has already cost us a fortune but we are supposed to move to AZ in two weeks and figured we needed ac. My grandfather told me that he didn't know what was wrong with the ac it just wouldn't cool anymore so he disconnected it and took the pulley off. So, step by step this is what we/my husband did:

1. replaced the pulley and all belts
2. discharged the system
3. ran 6oz of high mileage pag oil through it
4. vacuumed the system and replaced o-rings
5. charged with R134a, and it has a R134a fitting on it
6. worked great, cooled great, pressure was great, but noticed the valve leaking
7. replaced the valve stem
8. hooked the hoses back up and re-vacuumed the system and replaced the o-rings again
9. this time we bought the high mileage R134a in a kit with three can that already had the oil in it, when we started recharging, it was taking extremely long for the ac to suck in the freon, then the gauge was not showing pressure unless you let off on the trigger, so we hooked our actual ac gauge set to see if it was a faulty gauge and had the same problem.
We finished putting in the rest of the 3 cans, and noticed the ac was not getting very cold, like it did the first time. Tried revving the engine to see if it got colder not idling but it didn't.

1. When the ac was turned on, it showed no pressure
2. When ac was off it showed 25psi
3. When truck was turned completely off it showed 70psi

Left and went to the store, turned it on about 20 min after driving, it got cold for a minute then got warm. Got back home and my husband let some of the refrigerant out of the high side, then noticed the ac got down to 40 degrees within 2 minutes. Hooked up the gauges and it was showing pressure! Finally, we thought it was fixed, wasn't showing great pressure but was showing about 30psi on low side. This worked for about 10-15 min then we lost pressure and the ac got warm again. Checked the haynes manual and it said to watch the accumulator sight window. When the ac was running there were tiny bubbles filling up the window. The manual said this could be from a refrigerant or air in the line. Well we checked for a leak and there is none, but not sure how to check for air or to get it out without letting all the refrigerant out. We have already bought refrigerant twice, which is costly, not to mention the parts and oil.

As far as the FAQ's:
1. Did not do and if it has R134a fitting wouldn't this part be compatible?: Accumulator/drier must be replaced with an R134a compatible replacement.
2. How would I know this? - If vehicle is not equipped with a high pressure cut off switch it must be added.
3. Did this: Flushing the system to remove the mineral oil and debris should also be done.
4. Did this: O-rings should be replaced with either NBR or HNBR replacements.
5. Dont know what this is: Adjustment of the pressure cycling switch may also be needed to achieve the best performance.
6. Didnt replace this: In some cases an upgrade of the condenser may be required to achieve the original performance.

Hope this helps better answer my questions. My husband has fixed 100's of peoples ac's being a mechanic, to include older 50 and 60 models and has never seen this happen.

bromodragonfly on Sun June 19, 2011 3:26 PM User is offlineView users profile

Getting a little bit confused, it might be better in the future to state specifically which side or what you've got your gauges on when you're describing system pressures.

My rule of thumb is to always replace the drier/accumulator when I've opened up a system to replace parts or whatnot. It can absorb a great deal of moisture from open atmosphere quite quickly - and is probably quite dirty anyways, if it's been inside a system that's been running for a long time. I would definitely replace it when retrofitting to R134A, due to the fact that the vast majority of oil in your system will either be in the compressor, or in the accumulator due to migration.

Air is 'incondensable', and with Freon, it will try to migrate to the highest point in the system. You will have needed to pull a good vacuum from both sides of the system (in case your system does not equalize pressures when it is turned off, but you did state that it equalizes to 70psi static), and you will have needed to purge your hoses of air before allowing flow into the system.

Does your system indeed use a TXV, or is it an orifice tube? When you had the system purged, did you clean the metering device?

Your low side pressures are way too low, indicating that the evaporator is starving. This is probably the result of a restriction at or before the metering device. You stated that you 'ran 6oz of high mileage pag oil through it.' What do you mean by this? Did you drain the compressor of its old oil and then add 6oz of new?

My guess is that you're logging up oil inside the condenser or at the expansion device. Or there's some kind of debris that is becoming temporarily dislodged when you're purging off high side pressure. Another possibility is that the drier/accumulator is restricting flow back to the compressor - but you will need to clarify where you're observing your low-side pressures from.

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