Help needed!! I'm having a problem with my HVAC controls. It all started when I put a new battery in. Everything worked fine prior to that, but for some reason after putting in the new battery nothing comes out of the blowers on either heat or a/c in any speed. The rear defrost also doesn't work anymore. I've checked and replaced the HVAC 20amp fuse in the door and replaced the blower motor relay. I'm not sure what to check from here so any help will be GREATLY appreciated!, thanks.

 

I think the battery replacement is just a coincidence unless you shorted something during the replacement. Nothing in the HVAC or rear defogger systems is computerized so the power interruption would not affect them. They are actually rather simple circuits with only switches, relays and resistors.

We can eliminate the blower resistor module since you say none of the speeds work and the high speed setting bypasses the resistor module entirely. The fuse was the obvious problem source but you replaced that. Any chance the new one blew after you installed it (indicating you have a short in the circuit)? Beyond that, we'll have to do some testing at the blower relay.

Unplug the relay and use your meter or test light to check for power on the dark blue wire with the ignition on and the blower switch in any position except high. You should see some voltage which will vary depending on which switch position (lower voltage in the slower positions). Change the switch to the high position and you should see full voltage on the orange wire. If the power tests don't show the expected results, either the blower switch is bad or the wire between the switch and the relay is broken somewhere.

Check that the black wire has continuity to ground. If not, splice in a new ground and test again.

If all those things check out, try using your test light or a (fused) jumper wire to apply power directly to the purple wire. That should make the blower motor run regardless of the switch position. If not, either the wiring to the motor or the motor itself is the problem.

Do your seats still work? They share the same circuit breaker as the rear defogger. If the seats work but the defogger doesn't then we can eliminate that power source as the problem. That would lead us back to the HVAC fuse again since it's the only thing in common with the blower. Of course it could be something as simple as the HVAC controls somehow got unplugged. Or it could be a coincidence but I don't believe in that many coincidences at the same time.

 

Thanks for the info! I just checked the new fuse again and it is not blown and the power seat does still work. I did check the relay with a multi meter when changed that, here is what I got.
Red:12v
Orange: 4.3v when **** on high
Dark blue: 4.2v in all positions (except high)
Purple: 0v

 

There's something very wrong with those readings. The red is correct although I would have expected somewhat higher than 12V but it should match battery voltage. The purple is also correct since that's the output to the blower motor so there is no voltage there until you apply it. But the orange should show full battery voltage when the switch is in the high position because it bypasses all of the resistors. And the dark blue should show different voltages depending on which of the first three switch positions is used (and no voltage in the high position). Are you measuring the voltage between wires in the relay socket and a known good ground (not between wires in the connector)?

 

Hello, and sorry for the delay. I was away for a week. But there's good news and bad news... I discovered the problem but that lead to another one. So I was wiggling the fuses in the box inside the door and the fans were going on a off. So I pulled the HVAC fuse out and noticed that the terminals inside are fairly corroded (not sure why). But in trying to clean them up one of them broke.... Am I okay with only three points of contacts with the fuse or is that an electrical/fire hazard? And how would I go about fixing that?

 

As long as the broken terminal still makes solid contact with the fuse leg, you should be fine. However, it's unlikely that only half a terminal will continue to make good contact so it's something you'll probably have to fix at some point. You can replace the terminal contacts but you'll have to pull the fuse box out from the dash, find the right wire, cut it and remove the broken terminal, then insert a new one and splice it to the cut wire. If there is enough slack in the wires (I doubt that), you might be able to remove the terminal from the fuse box and crimp a new one to the end of the existing wire without having to splice the wiring.