Heater not working

Tiny
MRJAXX
  • MEMBER
  • 1999 CHEVROLET SUBURBAN
  • 5.7L
  • V8
  • AUTOMATIC
  • 189,000 MILES
I have been trying to get my heater to work with no luck. At the relay by the resistor I am getting twelve volts in, but then when I test at the resistor it is a low reading. When I turn the switch from low to high and only two of the modes work. Is this a bad relay or is it something else? Dash control and roof control will not work. If I bypass the relay and jump it to the motor it will work.
Your help is much appreciated. Thanks,
Todd
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Tuesday, November 15th, 2016 AT 5:50 AM

9 Replies

Tiny
HMAC300
  • EXPERT
When you turn the switch three of the resistors work that can be a bad resistor on high it runs through the relay to the blower the relay is under hood. Check the switch as I do not know how many speeds you have I am assuming four.
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Tuesday, November 15th, 2016 AT 6:21 AM
Tiny
MRJAXX
  • MEMBER
There is a relay right next to the resistor and I was checking the incoming power to the resistor straight out of the relay and got five volts. The heater switch has four settings and three different control panels in the vehicle and none work. I switched out the AC relay under the hood. I have current going to the relay in the dash compartment and if I jump that to the resistor the blower comes on. Also, I noticed that when I press on the AC button or recirculating bottom the lights so not come on could this be the problem if these controls do not have power?
Thanks, Todd
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Tuesday, November 15th, 2016 AT 7:00 AM
Tiny
HMAC300
  • EXPERT
It could be the control head which has to be scanned by a mechanic and or the relay for the blower. if you have a like relay try replacing it with that and see if blower works. you can also use the link provided on how to test the relay. But it may be control head which if you replace it will need to be programmed to your vehicle by a mechanic.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit
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Tuesday, November 15th, 2016 AT 7:55 AM
Tiny
MRJAXX
  • MEMBER
There are three control heads in the vehicle and none of them work, but as I was saying I have only five volts coming out out the relay which is puzzling me. I thought if a relay was bad nothing would go through.
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Tuesday, November 15th, 2016 AT 8:38 AM
Tiny
HMAC300
  • EXPERT
No, the control head may be supplying the five volts to activate it. And it is getting twelve on one side but not putting the twelve volts to blower. Red wire twelve volts, orange five, blue twelve, purple wire to blower. Other wire ground wire to blower will vary voltage depending on setting of speed. Black wire ground. Front control module supplies power to aux control.
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Tuesday, November 15th, 2016 AT 9:33 AM
Tiny
MRJAXX
  • MEMBER
Okay, so should I be looking for a control head? But why will none of the other ones work? I am confused.
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Tuesday, November 15th, 2016 AT 9:39 AM
Tiny
HMAC300
  • EXPERT
Have a mechanic scan for codes as another control head will need to be programmed and you wont be able to do that. If this is auto temperature control then it really possible to be something else causing it.
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Tuesday, November 15th, 2016 AT 9:42 AM
Tiny
MRJAXX
  • MEMBER
So you think it could be the relay that ties in just before the resistor?
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Tuesday, November 15th, 2016 AT 9:55 AM
Tiny
HMAC300
  • EXPERT
No, I sent a link on how to test a relay, but until you scan for codes you wont know what it is.
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Tuesday, November 15th, 2016 AT 10:38 AM

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