I have a 2004 Chevrolet Tahoe with the 5.3L V8. Tahoe has dual climate control. Today tahoe quit blowing heat… it’s only cold. All sides do the same like driver side/passenger side and front and back. If I turn thermostat down all the way and back to heat it will blow heat for just a few minutes in the front but never the back but last less than 5 minutes, then goes back to cold everywhere. THis will work once maybe twice but that’s it. I replaced the A/C compressor and dryer June 2015. Replaced one of the blend doors at the same time. Any ideas? Has another blend door gone bad?? Any help appreciated.
Title should say no heat.
The heating/AC systems in your vehicle have what are called blend doors.
These blend doors take the commands from HVAC control module.
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Tester
One possible fix I have heard is to turn everything hvac to off. Disconnct the battery for 5 minutes, then reconnect. Did you recently disconnect the battery? If that does not work you are looking at new actuators, not an uncommon gremlin, which is why I make sure all controls are set to off and use a memory minder as a safety precaution any time battery is disconnected. Other than that you can try an easy cheap replacement of the variable resistor for heat control.
Does the dash coolant temp gauge show the engine coolant is getting as warm as it normally does?
Check the fluid level in the radiator on a cold engine before you look at anything else.
IMHO Oldtimer and George have started in the right place. Your heat comes from your coolant, and you first need to ne sure that your cooling system is working properly and full before searching for other possible causes. If your coolant is low (leading to air pockets in the heater core(s), you’ll have no or possibly intermittent heat, and that’s what you have.
You also should have a valve in the heater hose line that turns the coolant to the heater core on (it opens when you turn the heat on to allow the heated coolant to the heater core) and off. once you’ve ensured that your cooling system is fully filled with coolant, not leaking, and properly purged of air, verify that this valve is working.
Next step is the blend doors. These mix & match the hot air being blown through the heater core with the cool air coming from the feed plenum, directed through the AC system when the defroster is operating (which in most modern vehicles it does whenever the heating system is on). Blend doors also direct the air to the desired interior vents.