AC problem Diagnosis needed

[1990new]

My AC rebuild went so well on Trixie, that I was beginning to consider myself a bit of an expert.
Today I got knocked back down to novice.

I did pretty much the same thing to Bessie as I did to Trixie (except that I installed a rebuilt compressor also) and Trixie's AC is working great.
Flushed out all the lines, condenser, and evaporator.
The compressor came without oil so I put pag46 in the compressor and also a little added an ounce to the receiver/dryer, a few drops
in the evaporator and the condenser.
Added new expansion valve (same one as I used on Trixie), and a new receiver/dryer.
Pulled vacuum on the system for an hour and 30 minutes. Shut off vacuum and vacuum still held after 30 minutes.
Charged the system with 9 ounces of 134a.

Here is what is happening:
With AC/Heater fan on high and ac switch pushed in, the compressor runs but the low side pulls a vacuum and high side is around 120.
No cooling at all.
When I turn off the ac switch and fan, the high and low pressure equalize to about 100PSI after about 10 minutes.

I suspect a problem with the expansion valve but it's new.. so what else could it be? or maybe it is a bad valve.. how do I know?
Need advice from a real AC expert.

[bravekozak]

eHow says:
Normal gauge readings will be between 30 and 45 psi on the low side, and 200 to 350 psi on the high side. The expansion valve can fail in one of two ways. When stuck open, it allows two much refrigerant flow, and a drop in high side pressure. A gauge reading of less than 200 psi on the high side will be seen when this happens. When stuck closed, a higher than normal high side reading will be seen. Typically, this will be over 400 psi and climb until the high-pressure switch shuts down the system. Very low or very high readings on the high-side gauge indicate a faulty expansion valve.

================================


My question to you: Is 9 oz. of R-134A enough? The sticker on my Festiva says 1.5 pounds of R-12. The rule of thumb is 80% of the R-12 amount.

[Flyin4stroke]

Sounds like you need more freon

[eurotiva]

Mine says .7kg or 1 lb 9 oz. You need more Freon

[1990new]

Thanks everyone for your helpful comments.
I added more R134a, and while it was adding the low side pressure went up but as soon as I shut off the charge line the low side pressure dropped back down to
near zero. But then high side pressure increased by about 50 psi.
The more I read about this it appears that I definitely have a problem with the expansion valve.
I removed the air intake box from the side of the evaporator so I could get to the expansion valve to see what may be going on.
Here is what I discovered. I left the ac off for a while and let the pressure equalize. I then turned it on, and noticed that at first the expansion valve got
cold and frosted up, the output side tube had a little frost on it but the tube wasn't even cold beyond that. after it ran a couple of minutes the frost disappeared
from the expansion valve and no cold air ever was produced.
I'm going to remove the evaporator again and replace the expansion valve with the other new one I have and see what happens.
I'm wondering if I somehow got to much oil in the line and clogged up the valve that way.
I will post again after I change the expansion valve, vacuum and recharge the system.

[tooldude]

The AC is undercharged, so I don't believe you can troubleshoot anything without a proper charge, it may be misleading. Although waiting for an "expert" to advise you, I will pass on some information from the FJC Inc. "Guide To Retrofitting R12 to R134a", some I will put in quotes. The effective percentage of R134a to R12 for retrofit has varied over many vehicles from about 75%-90%, (so 18.75 to 22.5 oz may be expected). "PAG oil is a poor lubricant and becomes corrosive in the presence of moisture and chlorine. There are different viscosities of PAG oil and when the wrong PAG is used the result is early compressor failure. Using PAG oil when retrofitting can result in poor system performance, and early failure because of the chlorine left in the system. Ester oil is the best choice for retrofitting R12 systems to R134a or for new R134a systems (system performance is improved). PAG oil may damage or remove paint." I don't know what type of o-rings are in Festivas-- "The new o-rings made of HNBR or Neoprene are a better quality than the older style NBR o-rings. Even though the product is superior, they are not required when using [an ester] oil. They are essential when using a PAG oil. PAG oil attacks and removes the elastomers, resulting in the cracking and splitting of the NBR o-rings". Specs for those with no manual, all FSM the same: oil cap. 10 'fluid' oz./300ml & 500 viscosity; R12: 1lb. 9oz./25oz. ; High Pressure 199-220 psi. ; Low Pressure 19-25 psi. ; IIRC, the R134a is going to run at lower pressures than R12 when providing max cooling, so higher pressures than R12 mean something is wrong. "Overcharging an R134a system by a small amount will cause high-High Side pressures and loss of cooling." After you get the max low temp you can achieve by adding small amounts of freon at a time (2 to 1 oz.), the reading will begin to rise 1 or 2 degrees, beginning to overcharge - requires a sensitive scale. The charging procedure given where the original R12 amount is unknown may be useful here where the proper weight of R134a is unknown;" Add 1 lb. of R134a to the system; then add 2 oz. at a time until gauge readings and duct temperatures are correct". If you haven't taken it apart yet, I'm thinking it would be better to add freon and attempt to get proper cooling, then troubleshoot from there.

[1990new]

Thanks tooldue for all that helpful info.
I did use ester oil when I did the conversion to R134a and at the same time put a new compressor on the 1992 GL that I sold last year.
For that one I did not disassemble and flush the components but did add a new receiver/dryer along with the new compressor.
For the 89 and 90 that I just completed, I did disassemble all the components and flush everything out so I used pag oil in them.
The rebuilt compressor that I installed on the 90 came with only the oil used for assembly and had no oil charge.

Yesterday afternoon I removed the evaporator and the expansion valve again. The expansion valve was definitely stopped up with visible debris. Apparently I didn't do
as good a job as I thought with my flush. I did another flush of the evaporator and high side tube from the receiver dryer to the evaporator, reassembled with my other new expansion valve and new seals, did a two hour vaccum and recharged with 18oz of R134a. That solved the problem and it's working now. I just hope I got all the crud out of the system this time.

Next time I do this, I'll use ester oil instead of pag though. Sound line I could face problems down the road with the issues you noted.

[1990new]

Thanks tooldue for all that helpful info.
I did use ester oil when I did the conversion to R134a and at the same time put a new compressor on the 1992 GL that I sold last year.
For that one I did not disassemble and flush the components but did add a new receiver/dryer along with the new compressor.
For the 89 and 90 that I just completed, I did disassemble all the components and flush everything out so I used pag oil in them.
The rebuilt compressor that I installed on the 90 came with only the oil used for assembly and had no oil charge.

Yesterday afternoon I removed the evaporator and the expansion valve again. The expansion valve was definitely stopped up with visible debris. Apparently I didn't do
as good a job as I thought with my flush. I did another flush of the evaporator and high side tube from the receiver dryer to the evaporator, reassemble
with my other new expansion valve and new seals, did a two hour vaccum and recharged with 18oz of R134a. That solved the problem and it's working now. I just hope
I got all the crud out of the system this time.

Next time I do this, I'll use ester oil instead of pag though. Sound line I could face problems down the road with the issues you noted.