It is normal for the a/c compressor to run with the mode switch set to defrost or mix. The a/c system dries the air for more efficient defrost/defog.
I don't think so.
If it's a 97 to 98 then it's probably the Blend Door actuator that is broken. If it's the first generation Mark, 93-96 check the vacuum line under the hood that goes across the intake manifold towards the back of the motor, blend door actuator broken, heater core shot.
Probably the blend door actuator is broken, big bucks for a mechanic to fix, usually in the $2,000 range
Sounds like the Blend Door actuator, a $6.00 part but about $2,000 in labor, the dash has to be removed to do the job right.
It's your blend door actuator, big job for a $6.00 part, the dash has to be removed to access unless your mechanic is a magician.
Under the dash and in order to fix the darn thing the dash has to be removed unless there is a new technique. At the dealer the price used to be $2,200. Ouch!!
WHICH COMPRESSOR, AIR SUSPENSION OR A/C.........???
It's probably the blend door actuator, which is probably broken. The part is something like $6.00 but the install is in the $2,000 area, the dash usually has to be removed. Common problem for the 97-98 models.
Check the blend door actuator.
Air conditioning compressor? air ride compressor? question not clear enough.
Assuming we are talking about the temp blend door actuator, if the air coming out of the heater ducts in the cab is cold and the temperature control is on hot and the engine is running and fully warmed up (195 degrees) and the coolant reservoir is on the full mark and both heater hoses under the hood are hot, you probably have a faulty temp blend door actuator. If you have one heater hose that is hot and the other is only warm or cold, you probably have a plugged heater core. If both heater hoses are only warm or cold you probably have a stuck open thermostat.
The air compressor was indeed created in the 1809 by German Mark Pork. As for where did he make air compressor tank, I have no idea about it but I am happy to learn that too.