There is a vacuum check valve under the hood at the back of the engine. It is either broken or you have a bad vacuum hose.
Running the engine hot repeatedly.
The front expansion valve is clogged.
The air conditioning drain is on the passenger's side of the firewall. If you do not have air pressure to blow into it to get it to drain then you might use something soft and flexible so as not to put a hole in the evaporator.
If the coolant level is okay, I would suspect a restricted heater core. Try flushing the heater core.
Blow Your House Down was created in 1984.
Blow Monkeys the Masters was created in 1984.
I just had this problem on my 2005 Impala. My fix was a new thermostat. I also had the symptom of the engine temp swinging from hot to cold.
There are four drains on the factory sunroof. Two in the front corner and two in the rear corners. The front two are the easiest to get to. If you have access to compressed air take a blower with and extended tip and blow air in the front drain holes. Make sure you clear any debris that may have fallen inside your drain channel. The rear two will be able to be cleared if you have access to a piece of 3\8 clear tubbing you can attach to your air blower and repeat the same process as you did for the front. If all fails take it to an aftermarket sunroof company in your area.
Check the fuse?
More than likely a stuck horn relay.
Your A/C needs recharged.
Blow into the mic in front of the fire