Hot air even when A/C on max?

'04 taco, got me an HVAC issue that's driving me nuts. It doesn't happen every time, but its definitely more often than not.

Basically, when I turn on the truck, no matter what position the fan and temp selection knobs are at, I'll get blazing hot air out the vents. I'll feel it on my feet first but definitely on the dash vents and I think defrost too. The solution, it seems, is to wiggle the temp selection knob a quarter inch away then back, then usually it'll kick the hot air off and start giving me cool air. Sometimes, it'll switch back to hot air randomly which is not good given I sometimes have the dog in the cab while I run in somewhere. It also seems like if I have the knob at the coldest setting it'll be hot air no matter, what so I usually leave the knob a bit less than max.

I'm handy enough to fix this but I don't know a thing about how hvac works in vehicles. Any ideas where to start?

Edit to add: I just tried playing with the temp and mode knobs with the key on, both of the servos seem to move as they should (as far as I can tell). Not an expert but I'd say its something other than bad servos.

 

Having the proper factory service manual - FSM - might help.

Go to the URL at the bottom of this post and scroll down to -> 2001-2004 Toyota Tacoma FSM.

You will see an Online Version and Full FSM File Download (39mb)

The Online Version does not work. Select the Download version. Bring it down to your PC and unzip it.

http://web.archive.org/web/20110102225436/http://www.ncttora.com/FSM/

 

Oh man that's awesome, I was looking for this just the other day just for general reference.

I did some more diagnosing, it was acting up bad this morning - turns out if I just put a tiny amount of pressure pushing in on the temp knob, it'll trigger the max heat. Not enough pressure to be affecting wiring in the back so I'm 99% certain its a bad heater control assembly. Gonna see if the wreckers can find me a heater control assembly in the morning. Stumbled across this thread in the process, same issue and this allegedly solved it.