HVAC glitching out?

I think something is up with my HVAC. I usually run the car with the defrosters on the whole time and set to 65-70 degrees with cabin air recirculating, but randomly while driving the AC will stop and keep recirculating warm air until I switch from defroster off so it blows into the rest of the cabin. When I switch out of the defroster, it will blow warm air to my face for 3 seconds but will always blow cold after.

 

I don’t believe it’s a refrigerant issue since I refilled this summer and no leaks thus far. It doesn’t seem to be related to RPM or any driving at all, it just stops randomly and bugs the hell out of me because no my windows start fogging up.

 

I have also noticed the AC controls sometimes change on their own sometimes, maybe faulty ground wiring somewhere or something. Or maybe like a cabin temperature sensor failed if we even have one? Not big of a deal, just annoying in the winter. This did just start happening as it has gotten colder outside.

 

The HVAC works fine if I don’t use the defroster at all.

First I would make sure the battery terminals are clean and tight. When I bought my 05 in late June 2004, a few months later the radio and hvac would do funny things. While getting the car ready for winter, I clean the terminals. After that the problem stopped. I remembered that I thought the terminals were not that tight when I removed them.

 

The past few summers my AC would cut out after a while. I replaced the relay for the system in the under hood fuse box, a $6.00 part from the dealer. That fixed that problem. I replaced that $6.00 relay in both my cars.

I got that idea from a post on here after doing a google search for the problem.

Is there a temp sensor in the HVAC that maybe is hitting the preset temp and shutting the AC off?

I swapped the relay with another in the car and the problem persists. I guess I could try replacing both in the rare event they’re both starting to fail. I’ll clean the terminals tonight and report back if there’s any changes.

 

If there is a temp sensor that might be the issue, but I would assume that it is in the HVAC itself and would require some soldering to replace. Not sure though.

I'm just spitballing...I honestly don't know if Subaru does have this type of temp sensor or not. I do know there are other vehicles that do read the temp on the windshield and adjust the AC accordingly during defrost conditions so it doesn't overheat the windshield, but they will cycle it, not just turn it off.