Posted: Sat Jun 29, 2013 4:38 pm Post subject: Interminent loss of power to the HVAC
I have a 2003 Impala. Sometimes when you turn the key to run the HVAC control unit has no power to it-the fan is inoperable at all speeds, the recirc/fresh air button doesn't change selection, A/C and rear defrost button can't be selected. About the only thing that works is the mode selector. I can tell because the A/C turns on if defog or defrost mode is selected.
Then after a few moments the HVAC unit has power and works.
I replaced the control unit with a new OE one and the problem is still there.
I don't have an electrical schematic for the vehicle. What could cause this? It's the only electrical issue the car has. I can't figure out what circuit powers the HVAC unit besides the 10 A HVAC/cruise fuse on the driver's side instrument panel fuse box.
I suspect it might be the ignition switch even though only the blower and HVAC seems to be affected. I don't have the wiring schematic to figure out what all is in the circuit to the HVAC control unit that powers it in run and start key position, but obviously power has to be switched through the ignition switch.
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