The blower motor stopped working suddenly. I can make the motor work if I hit it directly with 12 volts. I traced the purple wire back to a module (15-72530 I think) under the relay box at the firewall (see image below). There is power going in to the module but not power out to the purple wire when the key is on and motor switch calling for the motor to work. This module was replaced at a shop a few years ago ($400). I don’t mind replacing it but wanted to make sure my test was valid. Thanks!
I’d do a couple of tests first before replacing the module. Measure the voltage to the blower motor (with it connected) when you think it should be running. Does the wire going to it have 12 volts? If not , next disconnect the blower motor. Now does the wire that goes to the blower motor (with the motor disconnected) have voltage?
I think you have a bad"blower motor resistor block".
This is your part;
I’m not sure if it is on the fire wall (engine side), or under the dash below the glove box on the Park Ave.
You may want to verify the ground and control wire but it is very likely the blower module has failed. Rock Auto has 3 different brands available for less than $100.
Thanks for the replies. I will be busy today checking it out.
Good trouble shooting. I assume the blower speed control allows you to change the speed variably rather than a few fixed speeds. That kind of control requires a transistorized control circuit instead of using simple resistors. The modules either open or short when they go bad. When they short the blower motor has power to it at all times, even when the engine is OFF. Replacing the power module will most likely fix the issue but you should check the motor current after you replace the module. If the motor is drawing too much current than it normally should, it will cause the module to fail again before it normally would. You can check the current at the fuse for the blower. I would guess normal current draw should be around 8 amps or less.
Is this a manual or automatic HVAC system?
I appreciate the replies. It is an automatic system. And just to clarify, the purple wire to the motor has no power under any circumstance. I will admit to being a bit confused about the terminology here. Is the “power module” the component I have in the picture?
The blower control module in the picture controls the blower speed with a large transistor rather than several different sized wire resistors. It is likely that the transistor in the blower module has failed.
Is the “power module” the component I have in the picture?
Yes, that is the power module for the blower. It is in series with the motor so if the module fails ‘open’ then it is the same as having a switch that supplies power to the motor. The switch has to be ‘closed’ or making connection for the load to work.
Thanks, I guess my thought process tells me that if the red wire going into the module supplies it with 12 volts, but there is no power out to the purple wire that runs to the motor when power is called for, that would prove this part to be defective, correct?
Not necessarily. The black wire supplies the ground (0vDc) for the speed module. The red wire supplies 12volts to the module and the purple wire should supply voltage to the fan motor based on the amount of signal from the small grey/black wire. If you have 12volts on the red wire , but nothing on the purple, check the grey/black wire. Of course, the ignition should be on and calling for fan speed. I’m not sure what the low limit is, but with the ignition off you should have nothing on the grey/black wire, and with ignition on and fan speed set to max, you should probably have between 9 and 12 volts. If you have this voltage on the grey/black wire, AND the red wire has 12volts, And the black wire has good continuity to ground, and you still have nothing on the purple wire, then you can assume the module is bad. If you don’t have any signal voltage on the grey/black wire when you should, then the problem is probaly with he control panel in your dash or the computer.
I hope after a year the person has solved their problem.
Probably and hopefully, but since I was working on this problem for someone else, I thought I would update this info.
Yeah too late now. I don’t know where I was. I replaced the bower control module in my Olds for $25 from the junk yard. But it was on all the time whether the car was off or not. I suppose it also could cause it not to work at all but not my symptoms. If it were a resister though I would think that it would work on one speed but not others. Plus I’m not sure if a resister is used on an auto system.
No, resistor is not used on the auto system. You can tell by looking at them. The resister type has 3 exposed resistor coils that look like springs and has more wires connected to it. The auto system has a transistor block, which appears to be just a big piece of aluminum with heat fins, kind of looks similar to the rectifier module on some motorcycles, and only has 4 wires, red, black, purple, and a small black/gray wire.