This is a bit long to provide background. 1983 944 Denso 6e171 compressor
1/2 yr ago I had a nose seal leak that required me to reseal compressor. I flushed entire system , new hoses, resealed compressor and all was well, 37deg from the vents and perfect pressures. AC was fine and cold for about 3 mths until the rear mounting bolt fell out. Before I knew the bolt fell out, I had squealing from the ac clutch or belt (not sure) when taking off from a light and ac on. I suspect pulley was torquing over with engine on take off. This only happened a few times and for a few seconds until I could get home. I noticed manually engaging compressor at speed did not cause squeal . At home and upon inspecting, I found rear mounting bolt was missing and all compressor seals were leaking, Hooking up gauges, the low side was high and high side was low. But it was still blowing cold.
This weekend I resealed compressor again. I did not see any obvious scoring or damage of pistons or reed valves. Before and after resealing, compressor turned quiet and smooth. I suspected clutch was damaged and maybe causing the odd pressures, so I replaced with good used one and set gap to .55mm. Compressor held a perfect vacuum for over an hour, so I went to charging. Gauges showed same as before with 80 low side and 60 High side. Also, it would not take refrigerant no matter what I tried. Cutoff switch is fine and compressor clutch engages and compressor spins . Clutch would not cycle it remained engaged, but then it was not accepting refrigerant either.
What would cause it not to take refrigerant and the pressures to be so off? I thought maybe expansion valve, but I thought that would make normal pressures even higher on both sides ?
AC compressor won't take refrigerant
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Tom
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Taking everything you say at face value (no connector errors, gauge mix ups, unrepressed Schrader valves, etc.), it sounds like the compressor isn't compressing... maybe due to collateral damage from the missing mounting bolt?c5_pilot wrote: Sat May 02, 2026 7:43 pm This is a bit long to provide background. 1983 944 Denso 6e171 compressor
1/2 yr ago I had a nose seal leak that required me to reseal compressor. I flushed entire system , new hoses, resealed compressor and all was well, 37deg from the vents and perfect pressures. AC was fine and cold for about 3 mths until the rear mounting bolt fell out. Before I knew the bolt fell out, I had squealing from the ac clutch or belt (not sure) when taking off from a light and ac on. I suspect pulley was torquing over with engine on take off. This only happened a few times and for a few seconds until I could get home. I noticed manually engaging compressor at speed did not cause squeal . At home and upon inspecting, I found rear mounting bolt was missing and all compressor seals were leaking, Hooking up gauges, the low side was high and high side was low. But it was still blowing cold.
This weekend I resealed compressor again. I did not see any obvious scoring or damage of pistons or reed valves. Before and after resealing, compressor turned quiet and smooth. I suspected clutch was damaged and maybe causing the odd pressures, so I replaced with good used one and set gap to .55mm. Compressor held a perfect vacuum for over an hour, so I went to charging. Gauges showed same as before with 80 low side and 60 High side. Also, it would not take refrigerant no matter what I tried. Cutoff switch is fine and compressor clutch engages and compressor spins . Clutch would not cycle it remained engaged, but then it was not accepting refrigerant either.
What would cause it not to take refrigerant and the pressures to be so off? I thought maybe expansion valve, but I thought that would make normal pressures even higher on both sides ?
Yes, that is certainly possible. I’m no ac expert at all, but when inside the compressor, everything looks fine , sounds fine, Feels fine. Plus, I can’t imagine how a missing bolt and a little misalignment of the clutch (my theory) could cause such “possible” catastrophic damage.
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Tom
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The mysteries of pressure sealing do run deepc5_pilot wrote: Sun May 03, 2026 7:39 am Yes, that is certainly possible. I’m no ac expert at all, but when inside the compressor, everything looks fine , sounds fine, Feels fine. Plus, I can’t imagine how a missing bolt and a little misalignment of the clutch (my theory) could cause such “possible” catastrophic damage.
but it’s one of two things -- either the compressor isn’t actually pumping, or pressure is equalizing somewhere else in the system (assuming your measurements are accurate). The fact that it won’t take refrigerant points to the compressor not pumping in the first place. If you remove the belt and lines at the compressor, you can turn the clutch by hand and should feel suction and pressure pulsing at the ports. Back in the brick and mortar junkyard days (or mud and gravel?) -- that was the quick/crude test before handing over money. 
All good points, Tom. Yes, while rebuilding it on the bench and after installed in the car, I can spin the pulley fine in here suction in the pump.
I’m not sure if I can find some crackerjack AC place that can bench test to confirm pressure builds somehow or not . If the expansion valve is failed closed, I’m thinking it may not be able to draw refrigerant but my limited understanding feels like the pressures on both would be higher than normal, but maybe that’s if you already have refrigerant loaded. And beyond my understanding here.
I’m not sure if I can find some crackerjack AC place that can bench test to confirm pressure builds somehow or not . If the expansion valve is failed closed, I’m thinking it may not be able to draw refrigerant but my limited understanding feels like the pressures on both would be higher than normal, but maybe that’s if you already have refrigerant loaded. And beyond my understanding here.
I'm wondering if your gauge set is depressing the schrader valve in the service ports. They usually have an adjustable pin at the connector. You might get a shot of refrigerant as you are connecting, then nothing if the pin is too recessed.
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Petethepug
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Are you charging the system with the same hoses that allowed the charge last time?
I have always used the free rental gauges from auto parts store. No telling if same set or not. But pressures were similar when I tested aftet the bolt mishap. I did not attempt to charge as ac was still blowing cold.
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dr bob
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Since these are free-rent gauges and hoses--
-- As others noted, make sure the depressors are in place at the charge port ends of the hoses. This is a worry if you are still using R12 ports, much less if the system is converted and uses R-134a ports.
-- Make sure the valves on the gauge manifold are closed and not leaking.
After that--
-- Was the expansion valve replaced at any time during your AC work? They really don't like any debris at all.
-- Fresh oil in the compressor after each teardown? Same oil each time? (PAG and POE don't mix...)
-- New drier with fresh oil each time?
Guessing you are adding refrigerant with the compressor running, asking the compressor to draw the refrigerant in via the low-side port. You should see a swell in suction (low side) pressure as you open the refrigerant to the manifold. It's a good sign that refrigerant is actually available from the can.
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FWIW, I found a 4-port manifold and gauge set. Very handy, as it allows the vacuum pump -and- the refrigerant cannister to be connected at the same time. You need discipline on the valves and hoses of course, but the ability to vacuum the whole system plus the manifold and all the hoses means no air gets in between vacuum and charging. Less effort vs. purging hoses with refrigerant to clear the air out of them.
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I charge with liquid, engine off and system cold, through the high side port. It's by weight. I only need to add a little heat to the refrigerant bottle to get flow into the system. Then to the manifold to make sure it's not storing liquid. The bottle gets a bath in hot water from the tap in a bucket, then comes out to go valve-down on the scale for actual charging. Part of the reason for the liquid charge with engine off is the location of the low-side service port on the 928 -- under a tight hot mess of hoses including the upper radiator hose. I could do the whole thing with just the high side hose connected, since I usually charge there anyway, Liquid lows to the drier and expansion valve forward, but also back towards the compressor through the condenser. By the time I have things cleaned up and just the two hoses connected, the liquid has had plenty of time to evaporate before a running pressure check. If I need to adjust low-side pressure a bit, it's with vapor from the bottle this time.
-- As others noted, make sure the depressors are in place at the charge port ends of the hoses. This is a worry if you are still using R12 ports, much less if the system is converted and uses R-134a ports.
-- Make sure the valves on the gauge manifold are closed and not leaking.
After that--
-- Was the expansion valve replaced at any time during your AC work? They really don't like any debris at all.
-- Fresh oil in the compressor after each teardown? Same oil each time? (PAG and POE don't mix...)
-- New drier with fresh oil each time?
Guessing you are adding refrigerant with the compressor running, asking the compressor to draw the refrigerant in via the low-side port. You should see a swell in suction (low side) pressure as you open the refrigerant to the manifold. It's a good sign that refrigerant is actually available from the can.
-----
FWIW, I found a 4-port manifold and gauge set. Very handy, as it allows the vacuum pump -and- the refrigerant cannister to be connected at the same time. You need discipline on the valves and hoses of course, but the ability to vacuum the whole system plus the manifold and all the hoses means no air gets in between vacuum and charging. Less effort vs. purging hoses with refrigerant to clear the air out of them.
----
I charge with liquid, engine off and system cold, through the high side port. It's by weight. I only need to add a little heat to the refrigerant bottle to get flow into the system. Then to the manifold to make sure it's not storing liquid. The bottle gets a bath in hot water from the tap in a bucket, then comes out to go valve-down on the scale for actual charging. Part of the reason for the liquid charge with engine off is the location of the low-side service port on the 928 -- under a tight hot mess of hoses including the upper radiator hose. I could do the whole thing with just the high side hose connected, since I usually charge there anyway, Liquid lows to the drier and expansion valve forward, but also back towards the compressor through the condenser. By the time I have things cleaned up and just the two hoses connected, the liquid has had plenty of time to evaporate before a running pressure check. If I need to adjust low-side pressure a bit, it's with vapor from the bottle this time.
dr bob
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
Hi DrBob
have converted to R134a and the connector pins appeared in good shape. Valves were not leaking per my successful vacuum test.
Expansion valve was not replaced with compressor reseal 6mths ago. I did install a new dryer and flushed the entire system. All was good until the mounting bolt fell out of compressor forcing the recent reseal. I did not replace the dryer this time as six months old, but I capped it off so open to air no longer than if you uncap the new one and installed it. Since the compressor showed no signs of grenading, I made the assumption the dryer was safe to reuse. Fresh PAG oil in the compressor as that was the only component this time that was touched. Six months ago each component got the proper amount of PAG oil.
I strongly suspect a stuck open expansion valve as I think that would lineup with not being able to accept refrigerant and the high low side being basically backwards. Friday, I plan to take the compressor to a shop that can bench tested and confirm it’s still good to use. They also have the proper expansion valve so I plan to pick one up.
If compressor checks out and installing new, TXV and I plan to rent the gauges from a different store to rule out any possible problems there.
have converted to R134a and the connector pins appeared in good shape. Valves were not leaking per my successful vacuum test.
Expansion valve was not replaced with compressor reseal 6mths ago. I did install a new dryer and flushed the entire system. All was good until the mounting bolt fell out of compressor forcing the recent reseal. I did not replace the dryer this time as six months old, but I capped it off so open to air no longer than if you uncap the new one and installed it. Since the compressor showed no signs of grenading, I made the assumption the dryer was safe to reuse. Fresh PAG oil in the compressor as that was the only component this time that was touched. Six months ago each component got the proper amount of PAG oil.
I strongly suspect a stuck open expansion valve as I think that would lineup with not being able to accept refrigerant and the high low side being basically backwards. Friday, I plan to take the compressor to a shop that can bench tested and confirm it’s still good to use. They also have the proper expansion valve so I plan to pick one up.
If compressor checks out and installing new, TXV and I plan to rent the gauges from a different store to rule out any possible problems there.