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Compressor Problem...bad valves??

Dale7905 on Fri July 30, 2010 7:17 PM User is offline

Year: 1991
Make: Lincoln
Model: Towncar
Engine Size: 4.6 L
Refrigerant Type: R-12
Ambient Temp: 90
Pressure Low: 100 psig
Pressure High: 100 psig

Hi All,

While driving my TC yesterday the a/c was working fine. After about 120 miles of highway driving, the a/c stopped cooling and was blowing warm air.

After I came home and the engine cooled down I ran some visual and mechanical tests. With the engine stopped, the pressurre on both the low and high refrigerant lines was measured to be about 110 psia as I believe it should be for the outside temp of 90 deg F. I started the car with the a/c on max, blower on high. Both pressures remained the same and didn't change, indcaiting to me that the compressor was not working. The clutch on the compressor seemed to be spinning as it should so the compressor shaft was ( probably) turning. The accumulator and suction line was warm to the touch, which normally are cool. This leads me to think that perhaps a valve inside the compressor is bad making the compressor unable to to work properly.

I was wondering is my diagnosis is correct, or could there any other problems that would give these symptoms. Any comments would be appreciated.

Chick on Fri July 30, 2010 10:57 PM User is offlineView users profile

Are you sure the outer clutch driver was spinning? if not, tap the clutch driver inwards, being careful of the belts, could be a bad clutch gap, bad cycling switch, or if the compressor is spinning engaged, and bad compressor.. The fact that neither pressure changed when you turned on the AC leads me to believe it is not engaging..

Email: Chick


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Dale7905 on Sat July 31, 2010 8:39 AM User is offline


I'm certain the clutch is operating . With the a/c off and the engine running, the clutch outer plate was not rotating. With the a/c on, that outer plate does rotate with the pully driven by the serpentine belt, indicating the clutch is working. Since the outer plate is splined to the compressor shaft, the shaft has to be rotating and actuating the swash plate driven pistons...unless it is broken. If broken, I'd think that would create a lot of unusual noise. But it seemed to run as smooth as ever.

With the engine off, I was able to rotate the clutch outer plate ( thereby turning the compressor shaft) by hand and it rotated relatively smoothly. I tried turning the outer plate of the clutches on two other of my autos with working a/c's and got the same kind of response I got on the TC. So I think the TC's compressor appears 'normal' in that sense.

I like to try to diagnose as much as possible before I conclude its the compressor, but it sure looks like that's where the problem is.

Dale7905 on Sat July 31, 2010 6:19 PM User is offline


While doing some more research I found in my Lincoln TC Service Manual a table ( page 36-32-13 ) that shows possible causes of various a/c symptoms.

Specifically: For a compressor that is continuously running ( like mine does ):

High Pressure .... normal to low (mine was about 100 psig maybe just a few psi above the suction pressure)
Low Pressure.....high (also about 100 psig)
Component Causes...............(1) compressor low performance
(2) a/c suction line partially restricted or plugged....low pressure will be normal to high if pressure is taken at accumulator ( where I take the low measurement ) and if restriction is downstream of the service access valve ( the orifice tube is downstream of the compressor output and the service valve at the output of the compressor).

This makes me think a likely cause for my malfunctioning a/c (ie:not cooling) could be a plugged or partially plugged orifice tube which is at the input to the evaporator.

After taking apart an old compressor and seeing how the valves work. I find it hard to believe that the valves on my TC's compressor have failed. Since I don't think the compressors shaft is broken from other tests conducted, a plugged orifice tube seems like a likely cause.

Does this seem to make any sense to you? Thanks for your comments.

bohica2xo on Sat July 31, 2010 7:21 PM User is offline

A dead compressor is a dead compressor. Broken shaft or shattered reeds, it is not pumping.

A plugged orifice tube shows up as a low side below normal, because it is in the discharge line.

A plugged suction line would have to be between the accumulator and the compressor. That is a fairly large diameter line, and generally a blocked suction is the result of mechanical damage, such as collision damage pinching off the suction line.


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1stbscout on Sat July 31, 2010 7:23 PM User is offlineView users profile

Not likely... If the compressor was working and the orifice tube was plugged the low side would be very low and the high would be very high as there would be no way for the refrigerant to return to the low side.

The most likely cause of your problems is a compressor issue. Bad valves, broken shaft...... anything in between. Either way the expansion tube and accumulator will need to be changed and the system flushed etc.

Dale7905 on Sun August 01, 2010 10:30 AM User is offline

Thanks for all the observations and comments. They are really helpful and appreciated. Looks like my approach will have to be to get the R-12 evacuated and focus on the cause of my problem being a compressor malfunction.

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