85 QV AC saga help

I have been having problems with my ac. When I attempt to recharge the system, my low pressure is negative and the high pressure appears normal at 200 psi. I have replaced the expansion valve three times, believing the negative low pressure reading is caused by a bad expansion valve. Each time I examine the expansion valve after removal. Each time it appears to be closed. I try to blow shop air through the expansion valve with no success.

1. Cleaned ac lines with ac flush.
2. Replaced the expansion valve (38683) and dryer (33444).
3. Ran a negative vacuum for 30 minutes.
4. Attempted to recharge with 134A.

Any help and suggestions would be greatly appreciated.
Thanks,


Bill

 

I have a suggestion

 

I know. The previous owner converted to 134A. I have never heard of converting back to R12. What would cause the expansion valve to not work properly? I asusme it does not matter if my Ac system is R12 or 134a.

 

Well, it's close to impossible that you have had 3 bad expansion valves. So the answer is somewhere else.

When you say you "attempted to recharge with 134a," what do you mean exactly? Did you add the proper amount of 134 by weight initially or what?

 

If you take the expansion valve out you can check to see if it is functioning. Take the copper tube sense line and heat it up . Use a cup of warm water and either look inside the valve or blow through it. As the copper tube heats up the valve opens further.

 

It takes a little work since the oils are not compatible. I have done it "back" on two cars but it reqiures removal of the compressor, etc. to do it right. I had to let one sit and drip all weekend.

This is why I am on such a soapbox about preventing this disaster from happening to people. If you want to you can go back to R12. If you are told by someone you cannot, find someone else because they are either:

1. Ignorant.
2. Lying.

I did it 2 times in two different cars, one in 04 and the other in 06, and they are fine.

 

Absolutely right - there is no reason you can't go back to R12 for better cooling. However the choice of refrigerant is not what's causing your problem.

What is the ambient temp when your high side is showing 200PSI? If ambient is above 80F, 200PSI on the high side is rather low for 134. You could simply be undercharged. Again, how are you "measuring" the amount of 134 you are adding while charging?

also - You said you flushed the system. What did you use to do that and are you sure you removed it? If the flush materiel was not the proper stuff or it wasn't completely removed, it could have caused clogs in all the new exp valves.

 

I flushed the system with AC flush & clean. I then ran shop air through the system for about an hour, followed by a vacuum for 30 minutes.

The temperature was around 85 degrees. I used AC manifold gauges and the high pressure would climb up to 200 psi, but the low side would go to negative psi.

I added around 36 oz of 134a.

I will try to test expansion valve by heating the copper line.

Any other suggestions???

 

I just had my 1985 308 Qv a/c compressor rebuilt, new expansion valve, new filter drier. It would not keep the R134 in. Turned out to be a schrader valve! Now the system works good.

 

shhhh Doc might hear you.

 

That's the best thing that could have happened.

 

I would suggest checking that the evap is clear; disconnect the TXV from the evap and the low side line from the compressor, and blow (un lubed!) shop air through from the TXV side of the evap. Be sure that you can get full flow doing this. Also, do the same test with the high side line from the compressor through the condenser with the condenser outlet line disconnected.

It's not uncommon to have the condenser and / or evap seriously clogged after a 12->134a conversion; some of the oils used for 134a make a black gummy mess when combined with residual oils from the 12 installation.

(Also, with a bunch of gummy mess left in the condenser, even if the condenser isn't clogged, you may be poisioning each TXV you install....)

-frank

 

Your funny Doc!

 

My ac is now blowing around 42 degrees on a hot 85 degree day here in Florida. 134a is working for me. On a side note, does anyone know where to reattach the black and orange/black wire to the pressure switch behind the brake reservoir? I detached mine by mistake.