ok so i just bought a 2000 gmc z71 and the heat seems to work when it wants to.. it blows fine on all the settings just blows cold sometimes when it wants to. any ideas what could cause this?

 

Have you checked over your cooling system at all? Check your jug and make sure it's serviced up. If your coolant is brownish in color you prolly need to have the coolant system flushed. The DexCool is common for clogging up a cooling system when it gets old. When the truck is up to temp touch all the different hoses to make sure you are getting hot coolant flow, especially to and from the heater core. It might even be the a/c controls themselves, they are known to go bad. Hope this helps.

 

alright, thanks i'll give that a try when i get the chance.

 

Mine would get stuck on hot once a week or so. It sucked!! I had to ride with the windows down. There's a little motorized arm underneith the black cover below the dash. It controls the door that blends the cold and hot air. If you pull that black cover off, you can visually inspect to see if that part is getting stuck. I had to order a new one, it was OEM and only like 40 bucks. It seems like it was very close to the hump in the floor. BTW mine is a 2000 as well, so this may be your problem.

 

Sounds like a Temprature or Mode Door Actuator to me.

 

Dorman makes that actuator as well...