HVAC no comm
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Intermediate
Joined: Feb 2011
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From: Santa Fe Texas
HVAC no comm
Ok, here is the run down. I wired a nitrous system in for a buddy and everything was working great. as I was finishing up I was hooking the wires up to the ash tray switch panel and the switches have lights so you have the normal three prong switch. well as I was testing the switches to make sure I wired them correctly I had the feed for the switches plug into fuse #18 (HVAC) which is a 10 amp fuse. well long story short one of the wires coming off the switch came loose while handling it and touched another wire causing a short. it happened quick and stopped so I was thinking it popped the fuse. well after checking ALL the fuses in both fuse boxes I can't find anything blown but the car still has no A/C controls. the circuit going to fuse #18 is DEAD. when I run the diagnostics it has only 1 code in 40-bcm which is B0432 for the rear defroster. then HVAC says NO Communication. I can wire a hot wire to fuse #18 and get controls but this is only a band aid. Is there something I am missing? trying to return the car to my buddy but not in a "broke" condition. TIA
Tech Contributor
Joined: Jan 2007
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From: Dyer, IN
Ok, here is the run down. I wired a nitrous system in for a buddy and everything was working great. as I was finishing up I was hooking the wires up to the ash tray switch panel and the switches have lights so you have the normal three prong switch. well as I was testing the switches to make sure I wired them correctly I had the feed for the switches plug into fuse #18 (HVAC) which is a 10 amp fuse. well long story short one of the wires coming off the switch came loose while handling it and touched another wire causing a short. it happened quick and stopped so I was thinking it popped the fuse. well after checking ALL the fuses in both fuse boxes I can't find anything blown but the car still has no A/C controls. the circuit going to fuse #18 is DEAD. when I run the diagnostics it has only 1 code in 40-bcm which is B0432 for the rear defroster. then HVAC says NO Communication. I can wire a hot wire to fuse #18 and get controls but this is only a band aid. Is there something I am missing? trying to return the car to my buddy but not in a "broke" condition. TIA
You chose a fuse that supplies 12 volts to the actuators and rear defog relay.
First thing first.....disconnect that crap wired into the load side of HVAC fuse 18. With the key in the "on" position, you should have 12 volts on the line side of the following fuses in the passenger footwell fusebox. : HVAC #18, BCM13 #22, BTSI #21. If you have 12 volts to fuses 21 & 22, then the problem is isolated to the feed to fuse 18.
Once you have corrected the problem, wire the new switches using the schematic below:
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From: Van Buren Arkansas
Wounded Warrior Escort '11
Its fed from the ignition. How did you check all of the fuses? Visibly, you might not see it where as a meter, you can. Use the meter in the OHMS mode and go across the fuse itself if still plugged in.
Last edited by dgrant3830; Feb 21, 2011 at 08:39 AM. Reason: add image and corrected my mistake
Tech Contributor
Joined: Dec 2006
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From: Van Buren Arkansas
Wounded Warrior Escort '11
My schematic is for a '99...the OP didn't state what his is from. You've got a lot more resources than I do for sure. Also, I've found a couple of errors in mine over time...fyi. Yeah Lucky, you were right, it is parallel. If he's got power at 21, then the ignition switch isn't the cause and probably cooked the physical connection at the junction of the two.
Last edited by dgrant3830; Feb 21, 2011 at 08:40 AM.
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From: Santa Fe Texas
this is on an 02 Z06. I physically looked at the fuses and when I didn't find one that was blown, I broke out the voltmeter and did a continuity test on all of them. They all seemed to check out but I will pay more attention to the ones mentioned.
Like I said this was a temp solution to test the switches etc since the ash tray panel was used. I will admit that I used the "easy" way out by just touching the wire to the #18 fuse since it was the only keyed fuse in the foot well but wasn't going to leave it like this as a permanent solution.
Now with that being said the #18 fuse has no power to it at all, keyed or not. that why I was thinking it was another fuse. I am hoping it didn't fry the PCM.
Like I said this was a temp solution to test the switches etc since the ash tray panel was used. I will admit that I used the "easy" way out by just touching the wire to the #18 fuse since it was the only keyed fuse in the foot well but wasn't going to leave it like this as a permanent solution.
Now with that being said the #18 fuse has no power to it at all, keyed or not. that why I was thinking it was another fuse. I am hoping it didn't fry the PCM.
Tech Contributor
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From: Van Buren Arkansas
Wounded Warrior Escort '11
Not the pcm. As Lucky and I are showing you, fuse 18 joins with 21 in parallel at some point but both are fed from the ignition switch directly. You didn't say what year your car is and its obvious that there are wiring differences from some years to others.
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From: Dyer, IN
Perhaps, but in this case, fuses 18, 21, and 22, are all bussed together(parallel) fed from the ignition switch. If 12 volts is present(key in "on" position) at fuses 21 and 22, then the feed to fuse 18 has been damaged (which frankly, is hard to believe). To be clear, I checked the 02 schematic, and the fuse arrangement is the same.
To the OP, you say you "touched" the wire to fuse 18. Was the fuse removed, and you touched the wire to the fuse socket line side?
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From: Van Buren Arkansas
Wounded Warrior Escort '11
I agree with you totally. I'm thinking the only way to fry a wire is if he grounded it out and severely rather than what it sounded like that he touched a hot-wire to it.
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From: Santa Fe Texas
No the fuse was in place in case I had something wrong it would pop the fuse (in theory)... I simply was holding the wire to the top of the fuse (the pin toward the floorboard). Obviously it didn't pop the fuse at 18, even tho they tested fine in continuity I am changing the fuses with some spares just to be safe.
Tech Contributor
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From: Dyer, IN
No the fuse was in place in case I had something wrong it would pop the fuse (in theory)... I simply was holding the wire to the top of the fuse (the pin toward the floorboard). Obviously it didn't pop the fuse at 18, even tho they tested fine in continuity I am changing the fuses with some spares just to be safe.
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From: Van Buren Arkansas
Wounded Warrior Escort '11
Issue might be just behind or on the fuse block itself but before removal, you certainly want to disconnect the battery first. I truly do not know where those wires actually come together but a ventured guess is there at the fuse block.
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From: Santa Fe Texas
Thread Starter
Intermediate
Joined: Feb 2011
Posts: 32
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From: Santa Fe Texas
is there anything "upstream" to fuse 18? maybe a fusable link at the battery etc? I would think if it was something like that then I would have more on the car not working than just the HVAC
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From: Dyer, IN
Makes it hard to help, when you do not provide info based on suggestions. Do you have 12 volts(key on) to fuses 21 and 22?
Tech Contributor
Joined: Jan 2007
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From: Dyer, IN
Ok, and those are bussed together with 18. So the issue is betwen the buss connection, and the line side of fuse 18. Guess it's time to disconnect the battery, and open up that fuse box. As a quick check with the battery disconnected, you can measure the resistance between the line side of fuse 21, and line side of 18......based on the results soo far, it should read open.
Tech Contributor
Joined: Dec 2006
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From: Van Buren Arkansas
Wounded Warrior Escort '11
Per Lucky's schematic, you might want to make a quick voltage check for fuses 5 and 15 too and let us know. That connection passes through the underhood electrical center.
Last edited by dgrant3830; Feb 21, 2011 at 03:19 PM.