2005 blazer 60 000 miles ac compressor kicks on and off when heat control is on fullheat and only in defrost heater also not blowing warm air when full heat on in other settings hose from heater core also is cool to touch have replaced thermostat i will flush heater core but why is ac kicking in and out sounds like a sensor problem to me thanks harry

 

The A/C compressor will cycle when you have it in defrost mode. It does this to dry the air.