AC Wiring - Blowing fuses (78 F150 w/400)
#1
AC Wiring - Blowing fuses (78 F150 w/400)
I'm readying my truck to get the A/C "turned back on" and was looking to verify that the wiring is good.
(Note: Engine is running but I don't have the belt on the compressor)
Test-Results:
1. What I think is the "AC wire" for the compressor (#1 in the picture), this wire also runs to (#2 in the picture) on the carb. The other end of this wire runs back (#3 in both pics) and then back to the firewall by the AC.
2. When I hooked, what I think is the AC wire up and switched from Vent to AC the fuse blew. I switched back to Vent and replaced the fuse (35amp), worked fine - switched to AC - fuse blew again.
3. I UNHOOKED the wire at the compressor, put a new fuse in and have it on Vent. I could move to AC and back to Vent multiple times with no issue.
4. I then put a multimeter on the "AC Wire" while it was switched to AC to see if I could read anything. Fuse blew...
Q1: Is the "AC Wire" #1 the correct wire for the compressor?
Q2: Any idea what would be causing the fuse to blow?
Appreciate any help on this.
(Note: Engine is running but I don't have the belt on the compressor)
Test-Results:
1. What I think is the "AC wire" for the compressor (#1 in the picture), this wire also runs to (#2 in the picture) on the carb. The other end of this wire runs back (#3 in both pics) and then back to the firewall by the AC.
2. When I hooked, what I think is the AC wire up and switched from Vent to AC the fuse blew. I switched back to Vent and replaced the fuse (35amp), worked fine - switched to AC - fuse blew again.
3. I UNHOOKED the wire at the compressor, put a new fuse in and have it on Vent. I could move to AC and back to Vent multiple times with no issue.
4. I then put a multimeter on the "AC Wire" while it was switched to AC to see if I could read anything. Fuse blew...
Q1: Is the "AC Wire" #1 the correct wire for the compressor?
Q2: Any idea what would be causing the fuse to blow?
Appreciate any help on this.
#2
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#7
Test for power with both the #1 and #2 wires disconnected. It sounds like #2 was left connected when you switched the AC on. If so that #2 wire may be the cause for blowing a fuse. It is going to the carburetor throttle emissions control solenoid. Maybe it is faulty and grounded out somehow.
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#8
Yes, you have the correct wire for the A/C clutch. If the fuse blew with the compressor unplugged then I would look at two other possibilities.
Its possible the A/C mode switch is shorted (doubtful). The other area that I would look at is the A/C wiring harness itself. Ford uses two accessory wiring harnesses that plug into the main harness to power the A/C system. I've personally worked on several that had the insulation melted. It looks like Ford used some undersized wire when they designed these harnesses. The last one I rebuilt, I used a gauge larger wire to repair the harness.
Here are some pictures of one of the harnesses that I found melted:
EDIT: One thing I would do, unplug the solenoid on the carb. I really doubt this is the problem, I've never seen one short out. I would unplug it just to take it out of the loop, eliminate a possibility.
Its possible the A/C mode switch is shorted (doubtful). The other area that I would look at is the A/C wiring harness itself. Ford uses two accessory wiring harnesses that plug into the main harness to power the A/C system. I've personally worked on several that had the insulation melted. It looks like Ford used some undersized wire when they designed these harnesses. The last one I rebuilt, I used a gauge larger wire to repair the harness.
Here are some pictures of one of the harnesses that I found melted:
EDIT: One thing I would do, unplug the solenoid on the carb. I really doubt this is the problem, I've never seen one short out. I would unplug it just to take it out of the loop, eliminate a possibility.
#9
Thanks for the feedback guys. In test #3 I did have the solenoid (#2 wire) on the carb hooked up (it's actually always been hooked up) and it didn't blow a fuse when I switched to AC. I'll try another test with it unhooked to see what happens when only #1 is hooked up.
I will also trace-check the wires to see if I see anything suspect - the junction where the AC Clutch and Carb solenoid split had some bare wire on the Carb solenoid side but didn't look damaged/melted otherwise, I'll clean that up.
Mike, in the bottom right picture, where is that on the truck? (glove box opening, main gauge panel opening, ?).
I will also trace-check the wires to see if I see anything suspect - the junction where the AC Clutch and Carb solenoid split had some bare wire on the Carb solenoid side but didn't look damaged/melted otherwise, I'll clean that up.
Mike, in the bottom right picture, where is that on the truck? (glove box opening, main gauge panel opening, ?).
#10
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#13
I've got COLD air in the dent, and not just cool air !!
Hooked up the compressor, new lines (a 2nd new dryer) and a charge.
AC project is completed, bring on the heat !!
I made the lines a little long so that when I replace the motor (not anytime soon) I can tuck the AC compressor out of the way.
You can see there was a little fab work done, I had the old York mounting bracket in place because it has the tension pulley attached but since Im using a Sanden style compressor it didn't bolt on this side so I had to make a piece to join the two for stability on the tension pulley.
Hooked up the compressor, new lines (a 2nd new dryer) and a charge.
AC project is completed, bring on the heat !!
I made the lines a little long so that when I replace the motor (not anytime soon) I can tuck the AC compressor out of the way.
You can see there was a little fab work done, I had the old York mounting bracket in place because it has the tension pulley attached but since Im using a Sanden style compressor it didn't bolt on this side so I had to make a piece to join the two for stability on the tension pulley.
#14
#15
I used the "fixed" conversion bracket instead of the swivel bracket but still fabbed a small bracket to tie everything together for rigidity.
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Sburton
1987 - 1996 F150 & Larger F-Series Trucks
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07-22-2011 07:29 PM