At idle with the heat on, the AC compressor kicks on and off for about 5 seconds on, 15 seconds off. Do all these trucks do it or is this a bad sign?

 

be more descriptive. the hot/cold doesnt matter for AC compressor operation. thre mode the system is in is what matters. if the defroster or 'mix' is on, then yes it will kick on and off.

 

You got it. When it's in mix, the compressor kicks on and off in idle. On floor mode, it seems to stay off. So this is normal?

 

The compressor will cycle on and off, even in the winter. It's a feature to keep freon moving through the system in order to keep the seals wet.

Good luck with your ride.

 

wrong. the compressor cycles on and off in defrost andmix modes to remove moisture from the air, thereby defogging your windows faster and more effectively.

 

Another reason it could be doing that is because the pressure is low. If the ac is turned off then nothing should be running. If there is a leak then you will eventualy have low pressure in your lines. The pump turns on when it feels low pressure in the high side. If your system is completly empty it will stay on all the time. If you don';t use the ac just unplug the connector on top.