1994 VOLVO 960 AC COMPRESSOR CYCLING

[tomoni40]

Hi guys: My 1994 960 Volvo AC system compressor is cycling all the time. When I turn the system on,the clutch engages,but them start cycling on and off. I checked the system pressure with a gauge on the low side(The only one on this type of cars, No High side),and when the compressor engages the pressure reads 45 psi,and then when,it cut off,the pressure reads 25psi.The system of course does not cools,because the compressor does not remain on,enough to cool. I am assuming,that because of the 45psi reading,the system is not empty of freon,but that is my thinking,I could be wrong.I have tried to refill the system with cans,but it will not take anymore freon. I am suspicious of a faulty pressure switch.
I am open for suggestions.Any assistance will be greatly appreciated.

[danr960]

I think you are correct on the systems is short on coolant. But you are also wise to suspect a faulty pressure switch.

The only true way to address would be to have the system evacuated and then the proper amount refilled.

Then if it was still cycling look at the pressure switches.

Low side readings are not the correct way to evaluate, it is so dependent on air temp, how long the system has been off to equalize.

DanR '94 964 356,000 miles (122,000 on the new engine)

[jimmy57]

The system can have 45 psi in it with very little refrigerant. It is either low on refrigerant or there is an obstruction. Probably just low.
IF it is in upper 70's or warmer you can do a charge with decent accuracy by running engine at 1500 RPM (use mailer tube on pedal and ease it to that speed with power seat), fan set to next to high speed, and recirc button switched on.
Add refrigerant in increments and then after adding monitor the fat line out of firewall and the fat line from accumulator to compressor. WHen it is nearly properly charged these will be the same relative temp. The line from accumulator to compressor will be colder right after you add refrig since the refrig is going into accumulator, that is why you have to wait a couple of minutes in each step.
After the line temps seem cold and equal you will begine to have slow compressor cycling and this is normal.
Turn off recirc and monitor lines again and add a little more if the line out of firewall warms up noticeably.
If you add a can of refirgerant and the line out fo firewall doesn't cool down and the compressor cycling is still rapid and the cooling fan has come on and runs constantly then it may have an obstruction...STOP! no more refrigerant!