2001 GMC Sierra heater blowing cold air?

[cramsnomme]

my 2001 gmc sierra is blowing cold air, checked heater coil and its warmed up tried rocking it and nogo either. AC blows fine. No leaks at all. Is it the thermostat or water pump. plenty of coolant too.

[Matt M]

If it was the water pump the vehicle would over heat or leak fluid I'm sure its the thermostat.. Can't fix it right away get a small piece of cardboard to cover up some of the radiator (( SOME of the radiator)) to get the heat working

[Molson02536]

Originally Posted by cramsnomme

my 2001 gmc sierra is blowing cold air, checked heater coil and its warmed up tried rocking it and nogo either. AC blows fine. No leaks at all. Is it the thermostat or water pump. plenty of coolant too.

Two common items I have run into that COULD be your problem
First would be the mode door actuator and cam assembly.
It is located on the drivers side of the HVAC above the gas pedal.
It is fairly diffucult to replace.
The other common problem I have run into is on the passenger side. If you remove the dash end close out panel
(the panel up against the passenger side door). Inside there there is about 6 electrical connectors.
You need to find the (12) wire brown colored one (C4), the 6 wire brown (C5) and the 6 wire gray (C8). All the terminals need to be checked for backed out terminals, bent pins, loose or poor terminal tension.
Also if you open the glove box, to the left you'll see a small wire harness taped, going down.
That wire MAY rub against the metal dash frame and be shorting out. It too can cause your problem.
IF POSSIBLE, I would take it to a good shop your familiar with and have them scan the HVAC system for Trouble codes. If any of these codes are stored (B0229 B0263 B0268 B0408 B0414 B3770) You may have either of the 2 wiring issues.

If your wire harness is good then your temperature control actuator is bad. It's a little motor that moves the temp door. They are about $70 at the dealer. To change it you need to remove the knee trim panel on the passenger side (3 screws, 7mm socket). The actuator is in the center above the transmission hump. It has one harness plugged into it and 2 screws (5.5 mm). Take the screws out and it should drop straight down. Align the actuator with the lever on the door and put the screws in. Plug the harness back in. Turn your temp control to cold and remove the HVAC 1 fuse. Should be in the fuse panel on the drivers side of the dash. Turn your key to run and leave it on for at least 1 minute. Turn your key back off and put the fuse back in.
P.S. The trim panel is a PITA to get off, so while you have it off check to see if you have the cabin air filters and change them while you are under there.