Follow up to my '67 A/C problem.

[Barbara S.]

Here's the problem that I'm facing with my A/C system for my '67 coupe with factory Air.

Let me detail the situation. I evacuated the system to negative 28 lbs.
It will hold at that vacuum indefinitely. No leaks whatsoever. The a/c
pump is new, the drier is new, the expansion valve is new all the hoses are new.

The orignal parts used are the evaporator, the condenser, and the POA
valve. When trying to charge the system (from a 36 lb bottle of R-12 freon),
The pressures come up to about 90 psi on both the high and low sides. After
starting the car and engaging the a/c pump (the pump is running), the
pressure on the high side never goes above 105 and the low side remains
between 90 to 95 lbs. I thought that the rebuilt pump was defective, so
that pump was relaced with another rebuilt one from another source. The
results from the second pump were exactly the same as the first pump.

I would think that any restriction in the system would cause the high side to read higher than normal and low side to read lower than normal ( low - 36lbs, high 250lbs). But what else besides the pump would cause minimal pressure
differential between high and low?

Any brilliant ideas out there?
Thanks again!
Tony

[Joe C.]

Re: Follow up to my '67 A/C problem.

Tony,

Thanks for the more detailed background information. It sounds like you've taken all due diligence to do the job "right"! Although I'm not the most "brilliant" fellow in the world, with all the details provided I have to conclude three possibilities exist:

1. Debris (trash) exists on the suction side of the pump, which was not removed prior to evacuation/charging.

2. The unlikely possibility of a SECOND defective compressor.

3. Check for the presence of a strainer on the low side. If that's clogged/restricted, then it's likely the problem.

Joe

[Phil P.]

Re: Follow up to my '67 A/C problem.

need to check poa valve for dry crystals (moisture was in the system prior)---or the expansion bulb could have lost it's charge (it controls the expansion valve)you need to run the system at least 15 min. for it to stabilize---if you don't have a sight glass on the drier you will need a thermometer and a temperature chart from a repair manual for optimum charging--personal guess would be the expansion valve stuck---good luck

[Dick W.]

Re: Follow up to my '67 A/C problem.

If the compressor is, in fact, ok then I would consider Joe's suggestions plus a possibility of a defective POA valve. They can be rebuilt. The expansion valve, from what little I know, is not rebuildable.

[Barbara S.]

Re: Follow up to my '67 A/C problem.

The most logical problem I think is the compressor, but how can two be defective? I may see if a third is a charm. The POA is fine.

I'll figure it out!
Tony

[Jim T.]

Re: Follow up to my '67 A/C problem.

Tony I recommend removing the inlet line to the expansion valve and removing the very small stainless steel funnel type resuable filter. It could very well be stopped up with absorbtion material from the dryer you replaced. If it is you will also need to flush out the path from the new dryer outlet to the inlet connection of the expansion valve. A easy out gently inserted into the small screen and lightly twisted will remove the screen with damaging it. New screens may be available from a major parts store.

[Dennis Rosenthal]

Re: Follow up to my '67 A/C problem.

I would have to disagree about the system being blocked in any way. I feel it is the opisite. If it had a restriction, pressure would not stay even, and its common for the system to "freeze" at the point of the restriction. It is the lack of restriction in the system that says it has a valve/valves stuck wide open, or the compressor is indeed bad once again. Both the poa and the expansion valve are designed to add restriction to the system. AC works on the pricipal gas to liquid, liquid to gas...

[Barbara S.]

Re: Follow up to my '67 A/C problem.

Hi Dennis. I think you may be right. I'm wondering if I can bench test one of my two pumps to see if it has proper flow from low to high. Everything points to the compressor. Maybe I've got two bad compressors?
I tried filling the system again today, but no real luck. The system evaculated just fine, but when I went to fill it with refrigerant, the high only went to 125 and the low only dropped to about 87.
Tony

[Mark #28455]

sorry to ask a dumb question

Did you charge the compressor with the proper oil? Did you then rotate it several revolutions to coat all the internal surfaces before you ran it? If not coated with oil, it can score the internal surfaces and quickly fail when the compressor is engaged.
Mark

[Barbara S.]

Re: sorry to ask a dumb question

Yes, I put in some 500 vis oil for R12 use. I did rotate it to get some oil flow.

My POA and expansion valve are clear. I'm going to try a third pump just to see if I have the worst luck in the world and have two defective pumps.

Tony