HVAC controller blowing AC fuse
Thread Starter
Intermediate
Joined: Dec 2003
Posts: 28
Likes: 0
From: Kingston ontario
HVAC controller blowing AC fuse
Hey everyone,
For some reason, i keep blowing the 25 amp AC fuse.
I think it's something to do with the climate control computer.
The problem seemed to happen around the time when i couldn't get the recirculation button light to stay on. For the longest time, i never touched that button and always used the "auto" button.
Anyway, when i change the fuse, it's fine again until i try to use the climate controls again. When i do, it blows another fuse.
I've heard of people checking for cold solder joints in these units, so i took it out, disassembled it, and checked. I couldn't see any cold solder joints but i don't have a magnifying glass or anything.
Anyone know what this could be?
Maybe it's not that controller at all, but the temperature door is sticking or something? I think that's controlled by vacuum, though.
If you have any suggestions, i'd appreciate it!
Scott
For some reason, i keep blowing the 25 amp AC fuse.
I think it's something to do with the climate control computer.
The problem seemed to happen around the time when i couldn't get the recirculation button light to stay on. For the longest time, i never touched that button and always used the "auto" button.
Anyway, when i change the fuse, it's fine again until i try to use the climate controls again. When i do, it blows another fuse.
I've heard of people checking for cold solder joints in these units, so i took it out, disassembled it, and checked. I couldn't see any cold solder joints but i don't have a magnifying glass or anything.
Anyone know what this could be?
Maybe it's not that controller at all, but the temperature door is sticking or something? I think that's controlled by vacuum, though.
If you have any suggestions, i'd appreciate it!
Scott
Thread Starter
Intermediate
Joined: Dec 2003
Posts: 28
Likes: 0
From: Kingston ontario
Does anyone know how i can test the actuator door circuit?
I don't have a scan tool. Maybe i can at least check for shorts, or check for proper resistances, etc.
Scott
I have a 90
I don't have a scan tool. Maybe i can at least check for shorts, or check for proper resistances, etc.
Scott
I have a 90
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
The AC fuse feeds 12 volts to these devices when the ignition key is in run.
Does it matter if the engine is running or not running for the fuse to blow?
Rear Defogger Relay. Not likely the problem.
CCM. 12 Volts goes in on connector WC4 18AWG Brown wire. Signal name IGN 3. Not likely the problem.
AC Clutch Relay. Very possible. Disconnect the plug at the AC Compressor. Start engine. Turn AC on and see if the fuse still blows. If it doesn't blow, may be a shorted Compressor Clutch Coil or AC Clutch Diode.
Heater and AC Programmer. 12 volts goes to pin D1
18AWG Brown wire. Signal name (ignition input). Could be the problem since it drives the door motor for the Air Mix Valve Actuator.
Heater and AC Control Head. 12 volts goes in to pin 1 18 AWG Brown wire. Not likely the problem.
Daytime Running Lamps if you have that. Not likely the problem.
Does it matter if the engine is running or not running for the fuse to blow?
Rear Defogger Relay. Not likely the problem.
CCM. 12 Volts goes in on connector WC4 18AWG Brown wire. Signal name IGN 3. Not likely the problem.
AC Clutch Relay. Very possible. Disconnect the plug at the AC Compressor. Start engine. Turn AC on and see if the fuse still blows. If it doesn't blow, may be a shorted Compressor Clutch Coil or AC Clutch Diode.
Heater and AC Programmer. 12 volts goes to pin D1
18AWG Brown wire. Signal name (ignition input). Could be the problem since it drives the door motor for the Air Mix Valve Actuator.
Heater and AC Control Head. 12 volts goes in to pin 1 18 AWG Brown wire. Not likely the problem.
Daytime Running Lamps if you have that. Not likely the problem.
Last edited by Hooked on Vettes; Aug 17, 2006 at 11:20 AM.
Pro
Joined: Jan 2006
Posts: 667
Likes: 1
From: Centennial Colorado
Originally Posted by Hooked on Vettes
AC Clutch Relay. Very possible. Disconnect the plug at the AC Compressor. Start engine. Turn AC on and see if the fuse still blows. If it doesn't blow, may be a shorted Compressor Clutch Coil or AC Clutch Diode.
Pro
Joined: Jan 2006
Posts: 667
Likes: 1
From: Centennial Colorado
Originally Posted by Hooked on Vettes
AC Clutch Relay. Very possible. Disconnect the plug at the AC Compressor. Start engine. Turn AC on and see if the fuse still blows. If it doesn't blow, may be a shorted Compressor Clutch Coil or AC Clutch Diode.
Originally Posted by 93*Corvette
Sounds to me that when his compressor engages, it blows the fuse. I would disconnect the electrical connector at the compressor. If it doesn't blow the fuse then it has to be in the compressor.
On my car I was blowing the clutch fuse in my fuse panel. Sure enough, my clutch measure .9 (point 9) ohms, which is almost a dead short.
BAD
GOOD
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Thread Starter
Intermediate
Joined: Dec 2003
Posts: 28
Likes: 0
From: Kingston ontario
In a way, i hope that's what it is.
That way, i won't be tinkering with things under the dash, laying on my back on the seat, etc.
However, if it is that, do i need a whole new compressor?
Thanks again!
Scott
That way, i won't be tinkering with things under the dash, laying on my back on the seat, etc.
However, if it is that, do i need a whole new compressor?
Thanks again!
Scott
Pro
Joined: Jan 2006
Posts: 667
Likes: 1
From: Centennial Colorado
Originally Posted by sbzer
In a way, i hope that's what it is.
That way, i won't be tinkering with things under the dash, laying on my back on the seat, etc.
However, if it is that, do i need a whole new compressor?
Thanks again!
Scott
That way, i won't be tinkering with things under the dash, laying on my back on the seat, etc.
However, if it is that, do i need a whole new compressor?
Thanks again!
Scott
You can replace the clutch without replacing the compressor. But the way I see it, the clutch cost almost as much as the compressor. As easy as it's to replace and fill the AC unit, why not use a new compressor.
Thread Starter
Intermediate
Joined: Dec 2003
Posts: 28
Likes: 0
From: Kingston ontario
Sure enough, it was the AC clutch. When i measured the resistance, it's basically a short.
The hvac computer is staying on fine now, no more blown fuses.
Now i just need to find an affordable compressor or AC clutch, i guess.
Thanks again!
Scott
The hvac computer is staying on fine now, no more blown fuses.
Now i just need to find an affordable compressor or AC clutch, i guess.
Thanks again!
Scott
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
93*Corvette's pictures doesn't show the electrical plug. I don't recall what end of the plug the diode is on. (Plug connected to the coil or the mating end of the plug). If the diode is on the coil end you need to verify the diode is not causing the low resistance reading.
Taped inside the harness there is a diode across the AC clutch coil. When you measured the resistance of the coil you were measuring the two in parallel.
If the diode is shorted it could give you a false indication that the coil is bad.
To verify if the diode is bad you need to cut one of it's leads (solder it back on latter) and measure the resistance of the coil again. If the resistance across the coil measures around 4 ohms the coil is good.
Then measure across the diode. Place the meter leads across the diode and then reverse the leads across the diode. In one direction you should read low resistance and in the other very high resistance. If the readings are the same, the diode is bad.
Taped inside the harness there is a diode across the AC clutch coil. When you measured the resistance of the coil you were measuring the two in parallel.
If the diode is shorted it could give you a false indication that the coil is bad.
To verify if the diode is bad you need to cut one of it's leads (solder it back on latter) and measure the resistance of the coil again. If the resistance across the coil measures around 4 ohms the coil is good.
Then measure across the diode. Place the meter leads across the diode and then reverse the leads across the diode. In one direction you should read low resistance and in the other very high resistance. If the readings are the same, the diode is bad.
Last edited by Hooked on Vettes; Aug 18, 2006 at 10:19 AM.
