1967 eldo alc compressor

[bumpercarguy]

Can some one explain why the alc compressor will not shut off when line pressure is reached. The book says pressure difference between vacuum and atmosphere pressure when reached will sent unit at idle or shut off mode.Have benched tested at 70lbs 5 minutes to reach 120lbs  passed test. Holds pressure and passes the water test. What have i missed thanks P Foster

[Scot Minesinger]

Vacuum pressure is at most about three quarters of 1.0 psi (27.6 inches of water gauge = 1.0 psi) referenced to atmosphere.  References to 70 and 120 psi are past this mark and seemingly unrelated.

The switch that turns compressor on and off is shorted/stuck on. 

[cadman56]

Where is that cut off switch?  In 1988 I completed a major body-off restoration on my 67 Eldo & drove it over 16K miles before selling it.  My compressor never shut off.  The Cadillac mechanic ( an AC specialist there ) at my dealer advised the compressor just goes into a bypass mode.  I didn't like that so added a temperature controlled switch in series to the clutch wiring.  Worked like a charm & gas mileage went up.
Was he right or wrong? I wonder.
I am going to start on a 68 convertible this summer & plan on using an aftermarket expansion tube & clutch cycling switch set up.
Good luck, Larry

[bumpercarguy]

Scot on a 1967 cadillac eldo they use vacuum from intake manifold to  the level ride vacuum compressor.they toggle a lever to activate the rubber diaphragm to build pressure in the unit .Since vacuum is being supplied to the compressor all the time and compressor will not shut off that leaves me with a vacuum leak and poor engine idle .Need  to find out what shuts down the compressor when system pressure is met.

[Glen]

The first thing to remember is that the line pressure is set by the regulator on the side of the compressor.  The reservoir pressure is regulated by the vacuum available but normally goes to as high as 280 PSI.  The compressor is “shut off” when the vacuum can no longer move the compressor piston against the reservoir pressure.  In short the compressor stalls.  If you have any leaks the compressor may never shut off. 

Use a bubble solution to find your leaks.  The most likely place the system leaks is the shocks, especially if the car has been driven with no air in the ALC system.  That causes the air bags to deflate to the point the bags rub against themselves as the car body moves up and down. 

The shop manual also shows a method of finding leaks in the compressor by putting it in a bucket of water, but that requires removing the compressor and capping the three ports after filling the reservoir.     

[cadman56]

Sorry guys, I misread the first question.  Must need new glasses.  Larry

[Scot Minesinger]

Larry,

I think the compressor ran all the time so that you could dehumidify on a cold rainy day, say 40'F and raining in March so windshield would not fog up in defrost/fog mode.  Cadillac introduced temp switches for climate control a/c compressor to stop operation at 32'F, but not sure what year that was - mid 70's or so?  For our use (not cold rainy days), your solution is a good idea.

[Rob Troxel]

Not about the air conditioner.  Question is about the auto Level control.