When I turn my A/C on it will blow cold air. Then after a bit, sometimes a few seconds sometimes a few minutes, it will turn to hot air. It will do this constantly, usually staying on hot air longer than cold air.

A mechanic friend said to try resetting the temp control head by disconnecting the battery, then disconnecting the control head, and hooking the battery back up. I did it, but it didn't seem to help.

Any ideas of what might be making it fluctuate?

Also, if I'm just running vent I'll feel the air go from luke warm to hot and back and forth.

I've read some things on the blend door, or blend door actuator, but those threads only talk about the a/c or heat not working. Which isn't my problem.

Any ideas and suggestion are greatly appreciated. Thanks.

 

You could have a blend door failure. Blend doors can fail either hot, cold or act a damn fool. Do you hear any odd clicking noises behind the dash? If you move the temp all the way to cold, let it sit for a few seconds then go max hot does it make any click noises?

If so you need a blend door actuator. Yours may actually be vacuum controlled which could be the head unit has bad internal o rings and is loosing vacuum.

In that case look at this thread
https://www.f150online.com/forums/hv...buildable.html

Usually when a temp controller fails it will fail in the mode (floor, vent, defrost) switch. However if yours is vacuum like I think it is, it also could be the problem.

 

Im having the same problem. Except sometimes when I get on the gas to pass someone it gets warm/hot. Did you ever figure out the problem?

 

Depending on how much gas you give it the PCM will shut off the AC as it reduces engine power. The smaller the engine in the truck the more it will cut the AC out for power gains. Once the demand for power is less the AC will resume.

 

well the a/c doesnt go back to being cold again. it will stay hot for a while. sometimes for days.

 

Whens the last time you've had it serviced?

 

Thanks!

My head unit is vacuum controlled. I've taken it out and disconnecting everything from it, as someone said that would "reset" it. It didn't help.

I haven't noticed a clicking sound from the dash, but I have heard a sound, but it sound like bubbling, like something is boiling. It sounds like it coming from just behind the plastic near the floor board. I've checked my temps and everything is normal.

So, you think it's possibly the head unit has bad o-rings and is loosing vacuum and letting the blend door fluctuate?

 

Bubbling sounds is air in the heater core from low coolant level.

Bad orings in the head unit is very very common. I would change them out and go from there.

 

So, I finally had time to tear into the head unit last night. It turns out that mine is not like the one described in the EATC Rebuild thread. Mine is controlled by 3 *****. The ***** are obviously attached to posts, and each post goes into a different "module". The module that controls the temp has electric wires running to it. The mode selector (a/c, vent, heat) has the vacuum lines running to it.

Is it possible that the temp control module attaches electrically to a vacuum actuator down by a damper? And that actuator is losing pressure?

 

No. The blend door actuator is electrically controlled.

You have either a busted temperature blend door or a bad blend door actuator motor. I'd give 95% odds on it being the blend door. If I was in a bad mood, I'd say 99%.

It would have saved yourself and everyone else a lot of time if you had accurately identified that you had the three-**** manual controls instead of the EATC unit. Most guys hear "control head" and interpret that as EATC.