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CarQuestionGuy
CarQuestionGuy, Technician
Category: Car
Satisfied Customers: 1259
Experience:  ASE Master Auto Technician for 5 years, ASE Refrigerant Handler, ASA, iATN
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1998 olds 88: heater control..control module does not allow fan, a/c

Resolved Question:

1998 olds 88 heater control module does not allow fan, a/c and rear defog to come onnn
Submitted: 2 years ago.
Category: Car
Expert:  CarQuestionGuy replied 2 years ago.
How do you know that the control module is not turning these on?

Are the switches ok?
Customer: replied 2 years ago.
Dealer advised. On replacement module no fam, plus switches for A/C and rear defog not coming on.
Customer: replied 2 years ago.
Don't know how to check switches. Getting 12 volts from input with key on. Do not have any wiring diagram.
Expert:  CarQuestionGuy replied 2 years ago.
Are the problems exactly the same as before they replaced the module?
Customer: replied 2 years ago.
Yes. Only difference was on the original unit I had to pound on dash-it worked until the next time I had to restart the car. The 2nd. unit does not come on at all-just like the original control module.
Expert:  CarQuestionGuy replied 2 years ago.
When you say "fan" (in your original question) are you talking about engine cooling fan/AC cooling fan? Or are you talking about the blower motor?

The unit you have in there now doesn't work when you pound on the dash?

Customer: replied 2 years ago.
Yes. Blower motor for heater and air conditioning. No response when I bang on the dash
Expert:  CarQuestionGuy replied 2 years ago.
OK. Let's see if there is power to the blower motor, then we'll work our way back from there.

There should be a purple wire that goes to the blower motor. Turn the AC or heat on and see if you get power to that wire. Be sure that the key is in the on position.

Let me know what you find. If there is no voltage then we will check the blower motor relay.
Customer: replied 2 years ago.
No voltage on purple wire.
Expert:  CarQuestionGuy replied 2 years ago.
OK. We need to go back to the blower motor relay. This is the next thing in line.

There should be a red wire that is hot at all times, check for battery voltage at that wire.

There should be a blue wire that have voltage to it when the blower is supposed to be on. Check for voltage here, and let me know the reading if you find voltage here.

There should be a black wire that is for ground. You can check this wire with the ohms meter on a voltmeter. There should be no resistance.

Let me know what you find.
Customer: replied 2 years ago.
Only red wire I could find was spliced into a lighter red wire-could not get any voltage. No power to blue wire when key is on. Black wire is grounded.
Meter jumped very slightly when trying to get a reading on the red wire.
Hard to get probes into correct slot, but I believe I finally did.
Expert:  CarQuestionGuy replied 2 years ago.
OK. Check the voltage to the 30A AC maxi fuse located in the right maxi fuse block. There should be battery voltage at all times.

For the blue wire the key needs to be on and the blower needs to be turned on from the controls. Be sure the blower is turned on when testing this.

After you check the fuse we'll check the blower motor resistor.

Another thing you can do if you want is to exchange the blower motor resistor with another of the same kind. Then try to use the blower. This will rule out the relay for sure.

Let me know what you find next.
Customer: replied 2 years ago.
Was able to check fuses on driver's side-did not find any blown fuse. I am unable to get to passenger's side fuse block. (Too old) Only fuse on this side I noticed having to do with A/C Programmer. Everything else works. I did notice there is a light on inside the control module.
Where is blower motor resistor?
Expert:  CarQuestionGuy replied 2 years ago.
It is in the center rear of engine compartment. It should have 4 wires:

Dark blue
Light blue
Tan
Yellow
Customer: replied 2 years ago.
Too dark. Will be back tomorrow.
Expert:  CarQuestionGuy replied 2 years ago.
OK. Let me know.
Customer: replied 2 years ago.
checked 30 AMP fuse on back of firewall near the fan motor. Fuse checked OK but could not get any voltage reading on the circuit (A/C). Had key on and switch set switched to defrost where air should come on. Everything else on car working. I did not find a resistor.
Expert:  CarQuestionGuy replied 2 years ago.
So you had no voltage to the fuse?
Customer: replied 2 years ago.
Yes.No voltage
Expert:  CarQuestionGuy replied 2 years ago.
Hmmm...ok. That fuse should have battery voltage at all times. I don't know if you took the fuse out to test it or not, but take it out and test the terminals under it. One should have battery voltage.

Just to be sure, this is the 30 am A/C maxi fuse on the right maxi fuse block right?
Customer: replied 2 years ago.
This fuse was located on the firewall above the fan motor. Checked fuse for continuuaty and checked terminals for voltage-it registered just slightly.
Expert:  CarQuestionGuy replied 2 years ago.
What was the voltage?

Did it say A/C on it or near it?
Customer: replied 2 years ago.
Under 1/2 volt-not continuous, only when I inserted the meter probes. Then no reading at all.
Yes it was a 30 amp fuse.
Expert:  CarQuestionGuy replied 2 years ago.
Did it say AC near it or on it?
Customer: replied 2 years ago.
Yes. It was marked A/C
Expert:  CarQuestionGuy replied 2 years ago.
OK. There are several things we can do from here. The first thing you could try is to connect a long jumper wire from the battery to the terminals where the fuse connects (you can just remove the fuse).

Another thing we need to do is find out why there is no power to the fuse. You need to see if you can look under the fuse block (or remove it to see the wires under it) and check the wires under it to see if they have battery voltage. If they don't then you need to trace them back to the battery and find out where they are loosing voltage.
Customer: replied 2 years ago.
Found problem. Had to have dash removed. Attached to the dash was a connector with 2 burnt wires.

Thank you for your help anyway. I have a very high respect of your knowledge!
Expert:  CarQuestionGuy replied 2 years ago.
I'm guessing these wires were for the fuse that didn't have any power?
CarQuestionGuy, Technician
Category: Car
Satisfied Customers: 1259
Experience: ASE Master Auto Technician for 5 years, ASE Refrigerant Handler, ASA, iATN
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