Direct wire rear defrost

Good morning,

No, that would be a bad idea. The rear defogger is on a timed circuit. the antennae is a constant circuit. This means you can overheat the rear window and run the risk of fracturing the glass from too much heat.

Did you check the fuse for the rear defogger?

Make sure the fuses to the HVAC system in the fuse panel have power on both sides with the key on. The control head for the AC module controls the activation of the rear defroster and also controls the time based on ambient temperature.

Roy

The heater and A/C programmer receives the rear defogger request from the heater and A/C control assembly. The heater and A/C programmer will then send a Class 2 message to the body control module (SBM). The SBM will control the rear defogger on/off status and the amount of time that the rear defogger is on. The SBM will communicate the rear defogger status to the heater and A/C programmer over the Class 2 serial data and the heater and A/C programmer will light the rear defogger indicator accordingly.

thanks Roy, i didn't think about the timer. i did pull the large 40 amp fuse (it looked fine). I'll need to check the one under the dash next.

Okay, let me know.

Roy

Did you reply? I see you posted but nothing came up?

Roy

i deleted a comment that i meant for my other post. sorry about that.

No worries. Wanted to be sure I did not miss something

Roy

in my book/manual it says the fuse under the dash that controls the defog relay is the one marked IGN SEN. pulled and it looks fine. is there another fuse under the dash i need to look at?

I attached the diagram for you to view. Check the 40 amp fuse.

Roy

I also looked at every other fuse that was marked for HVAC, all look okay. next under the rear seat and that relay?

And the 40 amp under the hood.

Yep, test for power on both sides with either a test light or voltmeter.

Roy

I am getting a bit out of my league. I've never used a volt meter before. so many settings. i know it would be a good thing to learn to use one of these. I've always wanted to. can an old dog learn a new trick? volt meters for dummies, here i come. :)

Sure, let me attach a guide for you.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Roy

volt meter and multi-meter not the same. volt meter is a test light right? sorry i feel i'm taking up too much of your time. i'm off to learn a bit and will get back to you.

Voltmeter and multi-meter are the same things.

Roy

I'm with surprised how easy reading one of these is. thanks for the link. will be quite cool this week. will get back to you next week. thanks for all the help. Don

You are welcome.

Always glad to help.

Roy