The system has a mind of its own, the car only has 7k on it and the AC was recharged at the service in January. I can turn the temp all the way up and sometimes it increases the heat sometimes not. On manual the fan increases as you turn up the knob. The Auto buttons don't do anything to help.
Graeme
Graeme,
I have a Sierra SLT with dual zone electrical heating and mine has a mind of its own as well. Although mine does give good heat, I was setting it on auto in the winter time (-40F outside) and I had inquired about the same problem and this is what I was told how they work for all makes and model. The problem is when you put it on auto, if there is no heat in the heater core, the sensor sends a signal to the auto unit not to turn on and wait until it gets warm to prevent having the motor blow at max speed with nothing coming out for 15 minutes (assuming there is no problem with your heating system). Now on manual, yes the fan will go on because you’re overriding the unit saying to wait until the heater core gets hot.
Second, if you’re not getting constant hot air (when your engine temp is up to normal obviously) you have an air pocket in the system like Pete said. A heating system is a heating system no matter what car, make or model. So I would recommend you bring it to a shop to get this fixed. It’s not a hard thing to fix, anyone can do it, but if you’ve never done it before, you could make it worst because you have to read what the radiator is telling you (that’s for another conversation). My advice to you is once it's fixed, don’t use the auto setting again...they suck.
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