I've searched the forums and can't find what my problem is. On my way in to work yesterday, my air was blowing hot on the cold setting. When I left work, the air was blowing cool until I went over railroad tracks and it went hot. I stopped somewhere for a while and when I left again, it was blowing cool until I hopped on the interstate and floored it. Hot again. It runs hot with the AC on too.

 

What year is your truck? When was the last time you had the A/C serviced? Maybe you need some more freon or what ever they use.

 

how hot is hot? Like heater hot?

When it's blowing hot air with AC on, I'd say pull over, pop the hood, see if the compressor clutch is running.

If so, my guess is flap door valve/motor.

 

This is happening when the air is on vent at the coolest setting. AC on has no change in temp. The air is warm. It was in the 40s this morning and it was blowing 70-80.

 

definately flapper door switch/wiring/motor IMO.

 

The blend door? I just had to have my system fixed less than 6 months ago because of the heater core. Now it's hot and I have cooling problems..

 

agree with magnethread!!

 

The blend door is an expensive fix. Good luck.

 

Try disconnecting the battery and letting it sit for 15 min. Reconnect the battery and see if rebooting the computer recalibrates the doors, only a guess but may help.

 

You know, if it blowing 'warm' air, could it be the compressor not cycling all the time? Giving him A/C sometimes, then other times not? So while your trouble shooting everything before you buy parts, make sure the wiring harness going to your compressor is looking good. we do have a harness going to the compressor, right guys?