I have an 05 TL that has an issue that when I turn on the heater, the air conditioner on the driver side comes on and heater on the passenger side is also on. Even if the dual control button is at either "off" or "on", this still happens. The air conditioner works ok by itself. When I turn on the heater (set at 80 deg) even when the dash board shows that the AC is "OFF" the air conditioner still comes on. Weird! Has anybody ran into this issue? I would appreciate any info. Thanks All.

 

i dont think both come on.

What I think is happening, is a blend door or valve isnt opening. so, you get hot air in a couple of vents but blows cold in the others

 

Are you're low on freon? that happened w/ my wife's mini cooper 2 weeks ago and the dealer just refilled the freon and all good to go. But that's for the AC condition only. not the heater.

 

Yeah thats an uncanny issue you got there.
Agree with the above check your freon level.

 

or check the coolant level, since we're dealing with HEAT and not A/C

 

Same issue except passenger side blows cold SOMETIMES. Gonna try the valve control I keep reading about.

 

heater control valve could be stuck. happened to me a few years ago. one side of the car would blow cold when set to max high temp and the other side would blow outside ambient air temp.

 

as mentioned, check the heater control valve. its stuck.

 

Thanks justnspae for the info. I'll check it out.

 

The heater control valve had a leak and was leaking coolant. Had it replaced. No more leak but still have cold air when the heater is on. I'm having it checked again this week and keep you all posted.
Thanks all.

 

If one side is hot it can't be the control valve. It's a door not opening/closing. The car only has one heater core. If heat is intermittent it's worth a look at the coolant level, if it's severely low you'll lose heat at idle when water stops flowing through the heater core.

It's normal for the AC to run with the heat on, that's what defrost is but the heat should win the battle, the air gets dried by the AC and then passes through the heater core to be warmed up. It needs to be clarified if your AC is actually coming on or if the heater just doesn't work. On defrost the AC should run. Does the compressor kick on?