Intermittant hot/cold air from heater

Does the vehicle have dual zone climate control, where the driver side and passenger side have different control? Sounds like a blend door issue on the driver side. Why did you replace the passenger side, was it blowing hot too when AC was on?

Dual climate control on these is not a manual valve adjuster. It is done electronicly with a electric motor on a valve instead of ran by a maual cable. Find this and check the plug for a 12 volt signal. If you are getting a signal replace the valve, if not it could be a blown fuse, cut wire, or a bad climate contol switch.

temp blend door problem. either actuator motor bad, door broke inside heater box, or somthing interfearing with it closing. it could be an electrical issue w controller as well.

If it has dual zone temp. control it is most likely the heater control panel.

Take battery cable off for 5 mins, then put battery cable back on. Insert your key into the ignition turn to on but don't start the vehicle wait 5 seconds turn back off repeat the key on/off three times. This initiates a re calibration of climate control equipment and actuators. It will fix your problem.

you may need to have the controller re-calibrated. There is a TSB at the GM dealerships on this. What is happening is the the blend door control for the pass side has OVER-travelled and is stuck in a default position. You can try to pull the Blue fuse under your hood for the HVAC, for about 5-10 minutes and put it back in. (with the engine off) Then restart the truck and turn the Climate control back on, and push and hold the Auto button for 4-5 seconds

if it has dual zone climate setting it could be stuck in the cool setting. if it is not blowing any air it could be the duct came loose and it is blowing the air inside the dashboard. it will require you to pull the dash apart to inspect what the exact cause is. it could be anything from a bad temp setting switch in the climate control panel to a bad vac line that that switches the air from hot to cold. any other info you could give me may help such as if it is full electronic climate or manual knobs, dual zone, is it blowing any air or just no hot air.

You have dual zones that are controlled by temperature actuators the passenger side has lost its memory or has gone bad you can put it in self programming by disconnecting the battery for ten minutes then hook it back up start the truck turn the temperature control on but do not touch any other controls let it go thru the self programming for about 6 to 7 minutes then select your temperature you want if it still does not work properly you may have a bad actuator or a bad connection at the actuator

check the coolant level on the radiator..it sounds like its low

I had this happend to me on my 2004 2500 in july in S.C.I turned the key off and on 5-6 times and i have not had that problem again.