Cold air turns hot by itself?

First time post on this site. Visited several times, checked the sticky and didn't find a answer to my question. Here we go, 2002 Taco when the dial is set to cold some times it starts blowing out hot air. I have to turn the dial from cold to hot for cold air to start blowing cold again, sometimes it takes several times. What do I need to check?


Thanks!

 

I don't know the answer other than it may be a vacuum issue? Not sure on the newer models if the hvac is vacuum controlled, I assume it is because of the dial.
Bump anyway for somebody who may know...
Welcome to TW.

 

Check the valve on the outside firewall that the heater hoses go into,have someone tun the temp dial in the cab and see if the cable is opening and closing the temp valve on the firewall

 

Okay, I check that out. Noticed yesterday if I just turn the knob a little from cold it blows out hot air. No "range" of temp just cold or hot.