AC blowing hot air - relay bad?

brown42 · July 29, 2014

So how bad have I screwed this up? 2004 Silverado, 5.3. My trailer lights were not working, I was checking fuses and mistakenly left the key on while pulling and replacing a fuse. Heard some "arcing" sounds. As I was replacing a fuse, the horn started going off, like the alarm. Then the truck would not start. So I pulled the battery cable for a few seconds, replaced it, and the start starts. Finally found the bad fuses for the trailer lights and all seemed good.

But then started the truck, at noon on a hot Alabama day, AC started blowing cold air, then after 10 seconds the compressor shutoff and I get HOT, not just outside air temp, out of the vents. I pulled the battery cable again, left it off for 10 seconds, started the truck and got the same things.

The coolant temperature gage didn't budge off of the 160 minimum.

Any ideas? If I replace the AC relay on the fuse box, should that take care of it?

txab · July 29, 2014

Are you sure the compressor is not engaged? Air temp chang can be cause by actuator motors going bad or being out of calibration. With the electrical issue you had I'd think it might be the latter.

Try this first:

http://www.gm-trucks.com/forums/topic/151483-ac-stuck-on-defrost/?p=1330898

Try disconnecting the battery for
a few minutes. Reconnect it. Or remove the HVAC/ECAS fuse for a minimum of 10 seconds.

Re-install the HVAC/ECAS fuse.

Then turn the key to the on position, but
don't start. Don't touch the HVAC controls. Let them do whatever that
want to do. Air flow may change outlet points during this time. Wait
about 1 minute. Turn key off. Sometimes opening and closing the door can
make a difference as the vehicle controls see this as "cycle"
completion. Next start the vehicle and drive it a short distance and see
how it performs. You may indeed need to replace an actuator.

brown42 · July 30, 2014

thanks, will check asap.

Marine ferguson · June 27, 2020

hello my 210 gmc sierra 1500 is blowing hot air when i check the relay and took it out it blow cold air for like 20 minutes then it started blowing hot again.