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Need help with AC system on 1990 5.7

B

BG1

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There seems to be alot of AC information here so I am hoping to get some help.
On my 1990 Chevy I noticed during the winter when the temperature got down to about 7 degrees there was something leaking from the back of the AC compressor and it appeared to be compressor oil. The system will not turn on unless I put a jumper on compressor, the system worked good before the cold weather and it was converted to 134 about 6 years ago. I am guessing the o-rings at the hose connection to the compressor are bad and need to be replaced. Can I disconnect the lines long enough to replace the o-rings then pull a vacuum on the system and add freon? Should I drain the oil in the compressor and add the specified amount back to the compressor if I do have to remove it to replace the o-rings? Thanks, BG
 
The PROPER way to do the job would be to completely flush the AC system with flush solvent, replace the o-rings, do a leak test, replace the accumulator/drier, orifice tube, vacuum down the system and then recharge it.

There is no way to know how much oil is still in the system as it is not all retained in the compressor. Therefor the only way to know 100% for sure how much oil is in there is the flush it all out and refill it to proper spec. You could probably get by with putting a few ounces of oil in the compressor, vacuuming the system down and then recharging it, but you never know what to expect. It could have too little oil in the system or too much. Too much is better than too little, but it wont cool as well.
 
If you have the short big around compressor, it could also be the large oring,s that are under the outer housing. Check the source of leak carefully.
 
Some of those compressors would leak around the housing. Soap bubbles around the where the out casing meets together may reveal the source of your leaking. (That's the outer shell of the compressor body itself)

On a side note, at 7°F outdoor ambient, that saturation temperature is below the low pressure switch setting. In other words, it's too cold. When the temperature goes down, so does the pressure in the system. Checking just your pressure on a cold day can't really tell you if you are full or low on refrigerant.

The proper oil charge is a must too. The only way to tell would be to dump the oil and refill out of the compressor sump itself. This would require a removal and reinstall. Too much oil can destroy the compressor. Liquid oil enters the compression portion, and you can't compress a liquid. Something then blows apart or breaks resulting in a loss of pumping.
 
Best way to proceed is as follows.

Blow in some 134 to the point that the system will cycle. Inspect with a sniffer to see where the leak is.

Evacuate the system, repair the leak and recharge.

As mentioned the oil charge is a critical issue. This said if the oil leak has not been too large, adding a couple ounces of the proper oil shoudl be fine.


The seals at the hose connection area can and do go south.

Soap solution sprayed over the area may reveal the problem.

The High pressure cuttoff switch (if equiped) is also in the back of the compressor and can leak oil down all over the hose connection area too.

If your compressor has the switch, unplug it and see if the area in the plug is oily.

If this be the case, evacuate the system to ZERO "0" pressure and then remove the switch. (Snap ring holds it in)

Replace the switch and follow standard recharge procedures.

I prefer to use a "SNiffer" as you can pinpoint the source of the leak.

Another area of concern is the "CRIMP" where the hoses are mated with the aluminum tube/connections.

These do get tired and leak. (Been there done that)

Any system that has been an R12 system and then converted to 134A can have hose, O ring and other seal failures due to the incompatibility of the materials used during the R12 era with the 134A refrigerant.

If your hoses look at all suspect, replace them. The aluminum tube is unaffected.


Missy
 
Keep in mind: Compressors have different port heights to attach the rear lines. Some have thick washer seals to make up for a depth difference between the compressor and the lines. You may or may not run into this, but, pay attention to the old seal heights.

X2 for the compressors leaking around the body being common.

A sniffer used can tell you where all the leaks are and save you a compressor replacement bill or confirm it is leaking. Well worth the shop time or tool rental/purchase.
 
What orifice tube should I use?

On my 1990 Chevy 1/2 ton truck I need to get my AC working better, it had a leak at the o-rings at the rear of the compressor. I have seen where it is suggested to use a different orifice tube than the stock one to help get a lower temp at the dash vents, I have seen blue and yellow suggested but I would rather find out now if one is better than the other.
 
90 should be R12. That should be good'n cold. Define working better... like with how cold is your discharge air temperature, and if you are using MAX (recirculate) or Norm (outdoor air source). Norm at idle is not great. Max on the road is very cold. As long as your expectations are real for your climate and driving habits.
 
BG1 said:
On my 1990 Chevy 1/2 ton truck I need to get my AC working better, it had a leak at the o-rings at the rear of the compressor. I have seen where it is suggested to use a different orifice tube than the stock one to help get a lower temp at the dash vents, I have seen blue and yellow suggested but I would rather find out now if one is better than the other.
Click to expand...

The VOV, Variable Orface Valve is the best choice for R134a conversions. Otherwise stick with the white GM orface tube. The smaller ones (ford blue) tend to explode AC parts at high sustained road speed. Reason is ford blue is for Ford... Look up the VOV discussions on here for in depth. (Mainly the valve changes position for better idle AC performance over a stock white tube.)

Vac down the system and charge by weight -10% of R-12 charge for R134a. This is the only way to be sure of the proper charge.
 
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