Compressor clutch engaged with heat selected on 2004 silverado

Tap the clutch with a hammer lightly while a/c is on full blast. If it still doesnt engage its time for a new one. Future reference in the winter keep your heat on defrost some of the time, it activates your clutch in the A/C compressor so the bearings wont seize when you go to turn it on, on a hot day.

the obvious first, check freon... second, check fuses, and finally check that the clutch engages on the ac compressor when turned on (you should here a click and notice a small, momentary difference in the idling of the truck) you can also visually check the clutch by watching the compressor when someone else turns it on. if the clutch is not working, the inner part of the pulley does not spin.

Certain settings with the 'vent' or such can engage the a/c. Defrost can engage the a/c. Country music can engage the a/c.

There are a couple of things that could cause this.

First, a worn belt can result n slippage and squealing when the compressor load is applied.

Second, a worn out compressor clutch can result in a metal-to-metal contact when the clutch engages. This will cause slipping and squealing.

Third, the compressor shaft could be locked up, so that when the clutch engages, the belt slips over the pulley and squeals.

I suspect that the clutch bearing on your a/c compressor is failing. This would cause increased resistance to the spinning motion induced by the serpentine belt. The belt then continues to travel around the pulley on the a/c compressor, but the pulley doesn't spin and creates added friction on the belt. After a brief period of time, the belt heats up to the point of smoldering and begins smoking. When you select "defrost" you are engaging the a/c compressor clutch just as if you selected air conditioning. Take your car to an automotive repair professional for replacement of the a/c clutch bearing or, if the clutch is severely degraded, replacement of the a/c compressor. Good luck.

the ac clutch engages any time a defrosters on if you have a ac problem unhook the ac compressor that should take care of it till you have ac fixed

Depends.
The compressor will run when the control is in defrost, but should not in heat mode. In defrost mode the compressor runs to dry the air blowing onto the windshield.

1. Air conditioner system is discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
2. Air conditioner compressor clutch not engaging. Check compressor clutch wiring, electrical connections and compressor clutch, and repair or replace as necessary.

when defrost is selected a/c clutch is engaged and system automatically draws fresh air instead of cabin air.i woud strongly suspect compressor belt too loose and slipping or compressor seized and slipping belt.very easy to confirm visually.ever any squealing noise associated with odor?

If I'm understanding you correctly the a/c clutch does engage. Or is the compressor pulley spinning alone?
If the clutch is engaged thats the good news . Compressor is working and refrigerant is flowing.
Then your problem is with the blend door and actuator is defective.
If clutch is not engaged then you have to first determine whether there is frigerant in the system. Then you have to start at A/C on/off switch and go threw all sensors including ac fan relays to see what the problem is.
Unless your a trained HVAC Technician your best leaving this to a Technician.