1991 Chrysler New Yorker AC

My 1991 Chrysler New Yorker AC does not work as seen by the clutch on the compressor not turning when I turn on the AC on a hot summer day. The AC had been working prior to my Mechanic replacing the head gasket. I would like tyo authorize the mechanic to add R12 if needed but how should he test for this as a root cause?
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Scott CSenior EngineerCommented:
One reason the clutch won't engage is if the coolant level is too low.  Now that being said, if the coolant is low it's because it leaked out.  You need to find out if the level of R12 is correct.

If it's not, you don't want to put more in until the leak has been fixed as R12 is EXPENSIVE.

Test for leaks first.  Fix leaks.  Add coolant.  Enjoy cold air.
"One reason the clutch won't engage is if the coolant level is too low"
incorrect statement...

There is no coolant as it is a closed system like any air-con...
Freon R12 is pressurized in one coil  by a compressor then it absorbs heat when de-pressurized to a secondary coil.

Both coils have heat fins to help the process .
Similar to a car engines radiators fins.
If these heat exchanging fins are blocked with debris it will cause the air-con to shut down due to overheating.

Check that the heat exchanging fins are clean and that the fans work correctly.

It may just be old / worn belts or a seized air-con unit???
Low R12  will not affect operation. but will affect cooling performance.
R12 is cheap but service costs are expensive.
If the system has a leak then it has leaked the the R12 and it has also leaked the vital oils that lubricate the air-con compressor which will cause piston seizure.
Professional service is recommended.
Scott CSenior EngineerCommented:
No, that is not an incorrect statement.

I personally had a system that was low and the clutch would not engage, I watched as my mechanic added coolant and lo and behold the clutch engaged.

Of course professional serviced is recommended..  You must have missed the part where the Author mentioned taking their car to a "mechanic".

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To clarify my post,
Low Freon gas may cause the system to shut down depending on how the sensors work.

My wording "incorrect statement"...to your comment refers to the fact that:
"There is no coolant in a cars air-con system."

Refrigerant gas called Freon is not referred to as a coolant.

The Freon gas is  R12 or R22 or R134 and many other R???  when compressed turn to a liquid and when de-compessed  become a gas.
This causes a heat exchange which pulls the heat from the tubular coils with radiator like fins to produce cool air with the help of a fan that blows the air through the cooled radiator into the area needed to be cooled,
The hot air on the other radiator is expelled outside.
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