I have a 2002 cadillac deville compressor clutch will not come on with car running normally. tried to add freon but clutch would not engage. i went to a shop and a guy hook up this tool called MODIS to the interface and was able to engage the clutch but after running a few minutes Modis said the request was being canceled. he said the pressure was fine while the clutch was engaged but i dont know for sure. can you give me an idea of what might be the problem?

compressor pump clutch not engaging? try the fuse under the hood in the box right side

The most common problem on Cadillac A/C systems from the 1980s and 1990s is freon leaking out and causing the clutch to not engage.

Disconnect the battery and reconnect after a few minutes, then try to add a can or two of r134a to the system using a filler hose on the low pressure side port of the a/c system.

Sometimes, if the freon level gets too low, the compressor circuit will not turn back on at all as long as the car's battery has remained connected. This is a safety feature to protect the car from running the a/c clutch when there is no freond in the system.

Have you checked the freon level. If its low it won't engage. If you filled it and it still won't engage, unhook the battery to reset the a/c system.

First check to see if clutch will engage. Disconnect the plug on the accumulator and place a wire across connectors. This will engage the compressor. If compressor comes on, then what will need to be done is:
first be sure that all the connections and fittings are tight.
second replace the high and low side valves.
third have the system vacuumed.
fourth and oil and freon.

You should have a good working ac.

There is a problem with the air condition,econ,means the ac is not coming on,check to make sure the freon has not leaked out.If the freon is fine,see if the clutch is engaging on the compressor,if it is not ,then check the sensors on the liquid line ,along the firewall,they can go bad and the compressor will shut down,check all this and get back to me.

Sometimes, you have to start the vehicle, turn on the AC (Hi setting), and jump across (bypass) the low side pressure switch - to allow the compressor to start running and draw the freon in through the low side - make sure your fittings are correct and otherwise - Did you pull a vacuum on the system before you attempted to add refrigerant? I would highly recommend it - removes air and moisture....

To reset your AC compressor, you need to remove power for at least 15 minutes. After you reconnect, the compressor should turn on. If it does, immediately turn to high and try to add refrigerant. Best of luck.
Greg

Hi,check if the compressor clutch is engaging,if not check the conection at the compressor if ok check,fuse ,or relay ,if those are fine and the commpressor is engaging,check freon presure ,may be too high or low, if this is the case ,correct the problem and disconect the negative cable from the battery for a minute to reprogram the sistem..C1

In my 1990 Cadillac Deville there is a sticker that says that one can reset the computer that controls the compressor by disconnecting the battery for a few minutes and reconnecting.

Did you disconnect the battery to reset the a/c system?

The symptoms you are describing lead me to believe that there is a safety feature that prevents the compressor from engaging when the compressor has been run for any length of time without at least .5 lbs. of freon in the system.

You said that you had to run a hot wire to charge it up with freon. But, if you ran it without freon, it may have automatically invoked the 'safety' feature.

I have seen this happen on my 1990 cadillac. I haven't had any problems on my 1997 Cadillac Limousine, because I never had a low charge on that car.

you would be better off getting another compressor, used would be cheapeast, rebuilds are expensive