Wild Bill

I just had my compressor rebuilt after the front seal failed. Prior to that the A/C worked perfectly. I'm now having trouble getting any refrigerant into my system.

I pulled a good vacuum and started by adding one can of oil (2 oz. oil/2 oz. refrig) to the low side. I then started to add my first can of refrigerant to the high side. It would only take about half a can and raised the high side pressure to about 80 psi. I then started the car, turned on the A/C and attempted to continue to fill the system. The low side now shows about 85 psi and will not take any more charge and I still have close to half of the original can remaining!?

The compressor does come on and there is refrigerant moving trough the sight glass, but the low side pressure remains high and will not take more charge. I've tried increasing the RPM's, but it makes no appreciable difference on the gauge.

Any ideas on what could be going on here? It almost seems like I am having problems with the gauge or the tap or the low side schrader valve. What should I do to try and diagnose this problem?

TIA

Bill

dprantl

Whoa there.

- Did you add oil to the rebuilt compressor, or was it already pre-filled with the correct amount and type of oil?
- Are you using the standard gauges for this? I'm not exactly sure of what you mean when you say first you charged the low side, then the high side. When I charge a system, with the engine off I connect the can to the yellow charging hose and purge it at the gauge manifold, then I open both low and high side valves. If the whole can goes in, then close the low and high side valves, connect the next can and repeat. Once no more charge will go in and the can still has freon in it, then close the high-side valve and start the engine with the compressor running and continue charging only through the low side.

Dan
'91 928GT S/C 475hp/460lb.ft

Wild Bill

Hi Dan,
Thanks for chiming in... The compressor was empty. I had two ounces of liquid ester oil which I put in the compressor prior to installing it. I also had a 4 oz. can of charge oil which I added first to the low side to go to top off the compressor. I then started adding refrigerant through the high side, but it only took about half a can. I then started the car, but it will not take any more charge through the low side. My Robinair guage set is reading 85 on both sides and increasing the engine speed makes no appreciable difference in the readings.

Bill Ball

The compressor should get about 4 oz, although the initial 2 oz plus 4 in the low side should have covered that.

If the low side pressure does not fall and is the same as the high side that indicates that there is no compression happening. Something happened in the rebuild process. Is the clutch clearly engaging?

dprantl

According to my calculations, you should have 40% of 300ml of oil added to the replacement compressor, which is 4 oz. This is the amount you have added, so that's good. The rest of the system has ester oil in it as well, right? Did you purge the charge line of air before opening the low and high side valves for charging?

85 psi on both sides means the gauges are bad or the compressor is not pumping. Is the A/C belt on properly and not slipping? And the inside of the compressor pulley is spinning when you are charging, right?

Dan
'91 928GT S/C 475hp/460lb.ft

Wild Bill

The compressor clutch is engaged and spinning up the compressor and there is circulation in the sight glass. And, I did purge the lines... but, I don't want to admit that I've got a bad compressor on my hands.

That seems to be the only logical explanation. The refrigerant not going in would indicate the gauge reading is likely to be correct. The thing that eating at me is that I would have thought more than 1/2 a can would go in regardless of the compressors operating condition.

dprantl

Can you hear any noises coming from the compressor? Try to kneel in front of the car and put your ear as close as you can at the bottom. I'm sorry but I can't see any other possibilities than bad gauges or bad compressor if the clutch is turning with the pulley and you are seeing 85psi on low and high. Or... maybe you have blockage where the lines connect to the compressor?

Dan
'91 928GT S/C 475hp/460lb.ft

Wild Bill

I just got off the phone with the rebuilder and they say that if there is circulation that I may have a problem with the schrader valve on the low port of the gauge hose. He suggested I swap the hoses around which I had already done, so it may be the low side valve. I'm going to try unscrewing it bit to see if it will engage.

dprantl

That's something to try, but you put in that can of oil which is 2 oz of refrigerant through that valve on the low side, so ???

Dan
'91 928GT S/C 475hp/460lb.ft

blown 87

It goes in the low side, you can blow the can up hooked up to the high side if the compressor is running.

Bill Ball

Even if the low-side shrader is bad, if the high side pressure never changes - it should go up from resting pressure- this is good enough evidence the compressor is doing nothing. Also, unless you have the valve on the gauge set opened between high side and low, which you should not do, the low side would read zero if the shrader was stuck closed.

Wild Bill

Good news! I messed with the schrader valve and reattached using the high side hose on the low side port/gauge. Apparently I have some kind of problem with that connection plus a leaky high side valve on the gauge... but I have can #2 in and the system is now cooling and the pressure is back to where it should be 30 to 40 psi low side.

I need 37 oz for a full charge, so that is 14 x 2 + 4 for 32 oz... seems a shame to crack a can for 5 oz more. May run it for a while to see how it goes...

Thanks guys!

Ed Scherer

Based on instructions I've followed in the past, after adding oil to the compressor (like the initial 2 oz. you said you put in there, plus 2 oz. you injected to low side later), you should also manually turn the compressor slowly a few times (10 revolutions or so) to make sure that the compressor isn't attempting to pump non-compressible oil when it first starts up.

I believe this reduces the likelihood of the compressor breaking due to those initial start-up stresses.

FWIW, I just did a total system overhaul a few weeks ago (new compressor, new O rings everywhere, new drier/receiver, complete flush, etc.)

Wild Bill

Does anyone know where I can get rebuild parts for my Robinair gauge set or does it just use standard size o-rings?

Ed Scherer

Depends on what parts you're talking about. I just got a bunch of standard seals (O rings or whatever) that fit in the 1/4-inch female flare connectors (for R-12 hoses and other fittings) a few weeks ago at a local mechanics tool shop. Those happened to be branded MasterCool, but the fittings are standardized, so it really shouldn't matter.

eBay is a great source for all this stuff at good prices, if you can handle waiting a few days for delivery.