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I have a 1998 Suburban that has an issue with the a/c & heater control switch unit. The recirculation function does not work and the light does not come on. I pulled out the unit and it has a burnt-up resistor on the control board. I can't read the color codes on this resistor. Does anyone have one of these unit they can get the resistor value from? It's the resistor on the bottom of the unit, in a valley between a white piece of plastic and one of the green blocks.
SOLVED: The re-circulation (recirc) function and the max a/c function are working now (not sure if a/c was broken originally). With the fan on high I can now clearly hear the loudness and pitch of the fan change when the recirc button is pressed, indicating the recirc motor and recirc door are working properly. The fan is louder with recirc enabled.
According to this site it appears the burnt resistor is 3.8 ohms (not hundreds or tens of thousands of ohms, like everything else in the circuit). I was hesitant, but I replaced it with two 1-watt 10 ohm resistors (wired in parallel), versus the 1/2 watt resistor that originally came on the board. In parallel, the two resistors measured 5.2 ohms, which was close enough. This should give the new resistors four times the heat dissipation capacity compared to the stock 3.8 ohm one. I put my finger on the replacement resistors when the control unit was in the truck and they didn't even get warm.
As an interesting side note, this seems to be a defect in the control unit for all the models listed below (I'm supposing) since I have stumbled upon numerous photos of used heater control units on ebay and all of the photos that show this resistor show it slightly discolored, indicating it got hot at some point. The heat can also mess up the traces on the circuit board. Check for that.
I believe these are the units with this defect:
ACDELCO 1572548 {GM / CHEVY / GMC #09378815, 9378815}
ACDELCO 1572547 {GM / CHEVY / GMC #09378805, 9378805}
ACDELCO 1572330 {GM / CHEVY / GMC #16240135}
The white plastic casing of this unit is SUPER brittle after 19 year and impossible to flex (to remove the clips) without breaking. This is a bad design, GM. Just use long zip ties to hold it in place where the broken clips should be. It works fine. Also, the light bulbs are type 74, which are commonly available.
