2004 GMC Envoy Relay switch low beam & heater and AC fan.

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reclined
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2004 GMC Envoy Relay switch low beam & heater and AC fan.

Unread post by reclined » Fri Jul 05, 2013 12:55 pm

I have a 2004 GMC Envoy, the relay switch for the low beam burnt out about a year ago, so I replaced it, now it is not burnt out but it has burn marks on it. The second question is my heater and air conditioner fan quit working I can feel a little bit of hot and cold coming through the feet vent, number 5 speed has not worked ever since I bought it.

Thank You
Rhonda

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carriedi
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Re: 2004 GMC Envoy Relay switch low beam & heater and AC fan

Unread post by carriedi » Fri Jul 05, 2013 11:30 pm

your low beam signal goes from the headlight switch to the body control module (BCM). the BCM sends a the signal to the HDM relay #46. high beam relay is #43. If one leg of the relay gets burned you need to look at the relay connection. Usually if only one connector gets burned it's a poor connection. It means that when the relay closes the arc is not only at the relay contacts but there is an arc at the connector. the arc at the connector builds up heat and also makes the next arc look for a cleaner connection next time it is turned on. (Each time a connection arcs it burns a very small portion of the connection) Check the connector that looks burned and see if you can make it a tighter connection. Adding a little dielectric grease to the relay connection wouldn't hurt also.

Blower motor has a fuse in the under-hood fuse panel. #35 it's a 40A fuse. It powers up the blower control module. An electronic version of the blower resistor. the hvac module sends the signal for fan control to the blower control module. There is only one wire for the signal to the blower module. Unlike one wire for each speed and a bypass wire that a resistor has. The signal received by the blower module tells it how much to power up the blower motor. If you want to see if the problem is the control head or the blower module you need to look at the pu/wh wire that comes from the control head and see if the blower control module sees the fan request signal. You can unplug the fan motor and apply power and ground to the fan and see if the fan is the part is bad. (with the fan control on in a place where it used to work before, Bang on the bottom of the fan motor and see of the fans tries to come on. A lot of times the fan will be stuck in a dead spot and banging on the fan will bump the motor and it will activate again. But, that means the blower fan is bad.
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reclined
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Re: 2004 GMC Envoy Relay switch low beam & heater and AC fan

Unread post by reclined » Sat Jul 06, 2013 10:32 am

butchkaz,

Thank You so much!

Thank You
Rhonda (reclined1)

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butchkaz
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Re: 2004 GMC Envoy Relay switch low beam & heater and AC fan

Unread post by butchkaz » Wed Sep 18, 2013 3:45 pm

reclined wrote:butchkaz,

Thank You so much!

Thank You
Rhonda (reclined1)
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