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1998 olds 88: heater control..control module does not allow fan, a/c

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1998 olds 88 heater control...
1998 olds 88 heater control module does not allow fan, a/c and rear defog to come onnn
Submitted: 5 years ago.Category: Car
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Answered in 13 hours by:
5/23/2012
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
CarQuestionGuy
CarQuestionGuy, Technician
Category: Car
Satisfied Customers: 1,259
Experience: ASE Master Auto Technician for 5 years, ASE Refrigerant Handler, ASA, iATN
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How do you know that the control module is not turning these on?

Are the switches ok?
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Customer reply replied 5 years ago
Dealer advised. On replacement module no fam, plus switches for A/C and rear defog not coming on.
Customer reply replied 5 years ago
Don't know how to check switches. Getting 12 volts from input with key on. Do not have any wiring diagram.
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
Are the problems exactly the same as before they replaced the module?
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Customer reply replied 5 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.
Auto Mechanic: CarQuestionGuy, Technician replied 5 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?

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Customer reply replied 5 years ago
Yes. Blower motor for heater and air conditioning. No response when I bang on the dash
Auto Mechanic: CarQuestionGuy, Technician replied 5 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.
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Customer reply replied 5 years ago
No voltage on purple wire.
Auto Mechanic: CarQuestionGuy, Technician replied 5 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.
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Customer reply replied 5 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.
Auto Mechanic: CarQuestionGuy, Technician replied 5 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.
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Customer reply replied 5 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?
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
It is in the center rear of engine compartment. It should have 4 wires:

Dark blue
Light blue
Tan
Yellow
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Customer reply replied 5 years ago
Too dark. Will be back tomorrow.
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
OK. Let me know.
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Customer reply replied 5 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.
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
So you had no voltage to the fuse?
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Customer reply replied 5 years ago
Yes.No voltage
Auto Mechanic: CarQuestionGuy, Technician replied 5 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?
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Customer reply replied 5 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.
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
What was the voltage?

Did it say A/C on it or near it?
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Customer reply replied 5 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.
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
Did it say AC near it or on it?
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Customer reply replied 5 years ago
Yes. It was marked A/C
Auto Mechanic: CarQuestionGuy, Technician replied 5 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.
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Customer reply replied 5 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!
Auto Mechanic: CarQuestionGuy, Technician replied 5 years ago
I'm guessing these wires were for the fuse that didn't have any power?
CarQuestionGuy
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Satisfied Customers: 1,259
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