1990 GMC Siera Heater Relay location

IT BE NEXT TO THE BLOWER MOTOR WITH WIRES GOING INTO IT HELD ON WITH TWO SCREWS CALLED A BLOWER MOTOR RESISTER.

Hello! If your Sierra is equipped with a Heater Control valve it is near the firewall located in the inlet heater hose...From 1999-2000 a change was made and your vehicle may not use a HCV ...If it is there, here is the part # and price...

ACDELCO Part # 155686...$20

Send symptoms of the problem in a comment if you are having an issue with heat and a HCV isn't installed on your vehicle...Guru...........Saailer


I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

Thanks for the opportunity to let me help. The blower control switch in your vehicle also uses a blower relay. This relay is generally located on the firewall on the passenger side near the heater fan. You can also look in you vehicle owners manual for the location of the blower relay, it may be also be located in the fuse and relay box under the hood. Generally speaking if the highest setting doesn't work on a GM vehicle it is a high blower Relay. This item is not expensive and can be purchased at most all you local Auto parts stores. If you have a Napa, Orielly's, or AutoZone these stores will also likely help you in the location if you are unable to locate this relay. Here is a general picture The installation of this relay is either to remove from the fuse box, or if located near the heater fan housing then you will need to remove the mounting screws, remove the wiring clip, then reverse to install. I hope that this has helped you. D.R. Wilkins

it sounds like a faulty ignition switch or a bad connection from switch to relay also check the earth to the relay

Quite often you'll find resistor on firewall, of passenger side under hood. 1-1/2"x3" block attached to firewall. In area of where heater hoses enter.

Remove the glove box, you will see the relays, sounds like a bad ground.

does the starter make a "clicking noise" when it wont turn over? check your battery cables at the battery and at the starter solenoid....if it not a connection , then it sounds like a bad starter relay/solenoid

Hope this helps....

the heater blower does not have a specific relay. You need to replace the resistor located near the blower under the dash. It has a plug and a couple of screws.it may be a little difficult to get to .

The fan switch itself is a possibility, but there is also a resistor pack behind the glove compartment. Hi speed doesn't use the resistors, though, so if it doesn't run on hi, it narrows it down to the switch, the motor, the motor ground, or the blower relay, or any of the associated wire connectors.