86 C10 Silverado A/C Enigma

[half-fast]

System converted to R134 by previous owner. Worked fine. Compressor failed. Removed the compressor, flushed the system w/AC flush. Replaced the receiver dryer. Replaced the compressor/clutch with new ACDelco (not rebuilt), replaced orifice tube, fresh PAG46 oil. Pull a vacuum 20 minutes. Vacuum holds. Charge system. Works fine for about 2 years.

System stops working. Recharge. Works fine. Repeat several times.

System stops working again. System refuses to take a charge. Evacuate system, pull a vacuum for 20 minutes. Still does not take a charge- compressor is not developing pressure.

Assuming it's a bad compressor, replace the compressor/clutch with another new ACDelco. Pull a vacuum for 20 minutes. Vacuum holds. System will not take a charge. Assume the receiver drier is plugged. Flush the system. Replace the receiver/drier, orifice tube, both R12-R134 adapters. Pull a vacuum for 45 minutes. Vacuum holds. System will not take a charge and does not develop any pressure. Thinking my gauges/valves are bad, used a can tap and direct line to the low pressure port, bypassing my gauge set and 20lb can of R134. System will not take a charge.

During this process, I jumpered the low pressure cut off switch to engage the clutch for short bursts to allow the compressor to draw refrigerant in.

The low side gauge shows the compressor is developing a vacuum, but the compressor does not develop pressure.

This one has me baffled.
Do A/C hoses disintegrate on the inside and block flow the same way rotten brake hoses do?

[Tech II]

I am wondering if your service valves are actually opening when you are pulling a vacuum? If not, then you are only pulling a vacuum in your gauge lines.....

[half-fast]

Originally Posted by Tech II

I am wondering if your service valves are actually opening when you are pulling a vacuum? If not, then you are only pulling a vacuum in your gauge lines.....

Yes... I was thinking that might be the issue. So I replaced the R12/R134 service valve adapters with new ones and tried it again- no difference.

I also made up an adapter that connects my air compressor to the low side service port and applied compressed air to the low side- the air seems to pass through the valve okay.

I ordered a new condenser and set of hoses- the condenser is the original one from 1986 so maybe it is plugged. It's been through a few compressor meltdowns (black death). Once I swap those out the only part left is the evaporator... which seemed to flush just fine.

Still confused. Too hot/humid to work outside right now- have to wait a few days to pull the radiator & condenser.

[brcidd]

Never flush with anything you don't want to remain in there. Flushing agent is a degreaser and when you can't get it all out, you destroy compressors. This has been an ongoing issue with R-4s especially. No amount of vacuum will get all your degreaser out. That is why if I flush, I use refrigerant, that way, if some remain, it is no big deal. I'll bet your destroyed compressors smell like turpentine- due to your remaining flushing agent.