Auto Air Conditioning & Heater Repair: Heater / AC is draining my battery when the car is powered off., resistor packs, gmc suburban

Question
Hello,

I have a '93 GMC Suburban K2500.  I don't drive it very often (at 8mpg, I tend to need a good reason to take it out of the driveway) but, when I do, I 'd like it to start, the battery however, doesn't seem to care what I'd like.  If I don't drive it for a couple of weeks, the battery ends up dead.  After my last charge, a very car-handy friend and I tried finding where the drain was coming from, we found the 'Burb has a 37mA drain that is associated with the Fusable Link tied to the HVAC control unit.  When we disconnect the control head (I am referring to the controls inside the dash, where I choose Heat / AC, and fan speeds etc....) the drain drops from 37mA to ~4mA.  We've gone through and disconnected everything HVAC related we could think of (resistor packs, fan connections, vent/recirc doors) for both front and rear heat/AC and still read the 37mA drain.  I went to a salvage yard and bought a replacement control unit and it gave me the same reading.  I'm baffled and could really use some suggestions.  (I'd be OK with putting a switch in the line taking the 12V to the control head, but, I can't find a wiring diagram for the HVAC... I even paid for a full wiring diagram from an online site, however the only wiring diagram that they did not provide ended up being the one that I needed... grrr.)  Thank you for any suggestions you might have.

Jeremy


Answer
HI Jeremy

I do not believe that is your problem.  You will always have some current at the control that is what keeps it programmed.  When you start the engine it will keep the doors in the last position that you had.  If you disconnect it and reconnect you will see it will move thru the complete sequence and check all doors.  Look at the battery or something else.