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2005 F350 Blowing #24 Fuse with A/C on Only (No Tow/Haul, no Blower)
Let me start by saying that I have been Googling for similar situations for weeks, and for the life of me cannot find anything similar. Additionally, I would consider myself reasonably good at electrical diagnostics, and have eliminated as much as I can without replacing parts or digging into a wiring harness.
So, I've owned the truck for over a year, and never once have I had issues with blowing any fuses. About a month ago, truck wouldn't start, determined that the alternator wasn't charging, so I replaced the alternator. Went through 2 Napa alternators before going with a better company, and have had no issues since. About 3 days after replacing the alternator, I connect my 5th wheel, and we set out to go camping in the 90 degree weather. I realize just as we are pulling out, no A/C. After looking more into it, I could feel some cold air sitting in the vents, basically moving through convection, and it was actually the blower that stopped working. Also, no Tow/Haul function.
After determining that Fuse #24 under the dash, controls both the Blower and Tow/Haul, I checked in, and sure enough, fuse is blown. Replaced the fuse, and no issues the rest of the day.
The next day, at the camp site, with the trailer disconnected, fuse blows again. I get home, figure it must be the blower is pulling too much current, so I replace the blower motor, and the blower relay. No issues for two days, and then, fuse blows again. I pull the fan resistor, looks perfect. Just in case, I pull the plug on the resistor, and run the blower on high setting (only one that will work with the resistor disconnected), and the next day, the fuse blows again. Each time, I have no tow/haul feature. So, I disconnect the blower motor plug and wait for 3 days, fuse doesn't blow.
So, now I decide to plug the blower back in and just run the climate control in defrost, which still engages the A/C clutch, but hopefully narrows down the issue. A day later, fuse blows. So, now I know that its looking to be related to when the A/C is on. To confirm, I run the climate control in dash mode only, so no A/C function is turned on at all. Its been a week, no blown fuse.
So, I have thought about the shift lever issue where the harness shorts out, but the fuse never blows when I'm using the Tow/Haul function, only when using A/C.
Now I am thinking that maybe its an issue with the A/C compressor clutch coil pulling too much current, but that seems like a stretch. Especially because I think the A/C circuit has its own fuse that would blow if there were issues there.
I am pulling my hair out, but have no idea where else there could be a short. Sure it could be in a harness, but in my many years working on cars of all types, it is almost never within the harness (I've actually never experienced an issue within the harness, unless someone messed with it, or it was in an accident. Neither are the case here.
I'm really hoping that someone can show me a circuit diagram for the 2005 F350 blower motor, or if someone else has had a similar experience, or can offer insight that I may have missed.
The only other major repair was a transmission replacement over 3 months before this all started. I looked at all of the connections to the transmission, and they look fine.
This is a long shot but go trace wires to and from the AC compressor, the HVAC, the trans and the alternator. Pigtails, wires connecting from harness to clips, even where wire emerge out of loom, can develop small cracks, or wear spots which create intermittent shorts. I think you should narrow down to the most recent alternator work, look for where you could have disturbed a wire loom, clip, plug, ect. It's easy to bump, lean on, stress these things and cause these types of weird short issues. Maybe Yahiko will post some wiring diagrams for you too. They can be very helpful. You may also help to measure continuity on some of these wires if you can find something more obvious. I find shining a bright light on what I am inspecting helpful. Eyes are not so good anymore.
Its been a few weeks, and I have looked over all of the connections, and they look fine. Nothing obvious. I am now wondering if it might be related to the climate controls in the dash, or possibly something electronic behind the dash.
Does anyone know where I can find a circuit diagram of the hvac system in the 2005 Ford truck? I am thinking my next step is to trace down the voltage path through the dash controls out to the fan, etc.
As mentioned before, I have completely eliminated the fan and the fan resistors (unplugged both), and if I switch to A/C or Defrost, the fuse will eventually blow (but not immediately). I have been using the heat and all functions other than A/C and defrost for the last month without any issues blowing the fuse. Really strange.
AC and defrost both use the compressor. That appears to be the common denominator. Compressor doesn't turn unless the clutch is energized. It seems like the clutch may be pulling too much current. You need to get a load reading on the clutch at initial engagement and while running.
AC and defrost both use the compressor. That appears to be the common denominator. Compressor doesn't turn unless the clutch is energized. It seems like the clutch may be pulling too much current. You need to get a load reading on the clutch at initial engagement and while running.
Good point, however OP mentions he did use just defrost for a week with no issues so that would rule out clutch perhaps?
Nevermind, I see he ran only blower for a week no issues.
Can anyone confirm if the clutch itself can short to ground? Never seen or heard of it but it seems possible.
Good point, however OP mentions he did use just defrost for a week with no issues so that would rule out clutch perhaps?
Nevermind, I see he ran only blower for a week no issues. Can anyone confirm if the clutch itself can short to ground? Never seen or heard of it but it seems possible.
It can and I have read about cases of it. Also there is a diode in that
circuit that could also cause problems. Both are easy to test with a meter.
I have the same issue... where is the Diode? No one seems to know
The PDFs are no longer up and without finding then I would say you will find the diode in the clutch coil circuit.
On page 54-2 and for the EACT 55-2 you will find the diode.
Likely you might find it near the A/C relay in the BJB. It's not listed as the listing is just the fuses and relays.
I see by reading the diagram that for the manual A/C the diode is in the CJB and the same for the EACT system.
I didn't see it mentioned but if the fuse is the tow/haul then I'd suspect the tow/haul switch wires that come out of the shifter and pass over the steering column area are known to chafe and ground out. I'd start there or atleast look at the wiring schematic.
09-11-2015, 11:53 AM
