Hello all,

I have a 1998 C class RV with the dash Air Conditioning that is shorted out, it keeps on blowing the 15A fuse when turned on to Norm A/C or Max A/C or Mix or Defrost settings on dash only.

For troubleshooting I have disconnected the engine Air Conditioning Compressor plug to verify that it isn't the fault.

I've removed & replaced the switch that controls the dash a/c to defrost settings and worked for a minute, but now continues to blow the fuse as before. I'm not ready to buy another switch for now.

Is there a common item that may contribute to fail or common wiring that I should look at. I purchased the full electrical and service manuals but haven't dived into the ohm checks of the wiring, wire by wire yet. Tight wiring areas under the dash.

Also the fan speed controller works when in VENT or FLR modes, so I don't believe that is the problem, also temperature vacuum controls work.

Thanks to any insight from the experienced mechanics.
Thanks, Mac

 

Looking at my EVTM from 2000 there are several switches and a diode running in conjunction with the A/C compressor---since you're blowing the fuse only when A/C is selected it has to be a dead part or short in one of those.

I'm assuming its Fuse #13 that blows?

This might also be the clutch itself has failed. Disconnecting it and the fuse remaining intact says something in that whole circuit has failed.

FWIW I've rarely heard of that electro-vacuum switch itself failing like this----but of course anything can happen.

 

Thanks JWA,

Yes the fuse #13 blows, but the A/C clutch connector is currently disconnected for troubleshooting.

Where would I find that diode? Lots of wiring under the dash, arrrrgh.

Thanks, Mac

 

Most of what's potentially causing your issues would be under the hood, perhaps close to the A/C compressor itself. Going backwards from the compressor connection the diode is somewhere between that and an underhood inline splice, C121 for those with an EVTM.

Still underhood and leading back to the dash switch you'll find "A/C pressure cutout switch" connected to C159 most likely located near the radiator support, right/passenger side on the high pressure line.

Still underhood, "A/C clutch cycling pressure switch", connector C161, located above and to the rear of the battery. This then leads back to the dash switch.

Any of those switches along the line to the A/C clutch could be faulty. I MIGHT be able to dig a working image off a CD-ROM of an EVTM but please don't rely on me for that---can't be sure it would reproduce properly here.

You might also post this in the Electrical & Wiring Forum----its more electrical in nature, not as much the A/C system. If its the clutch that's another matter altogether.

Sorry can't be more specific and/or helpful.

 

Update:
I disconnected the connector C116M/C116F to split the system for troubleshooting.

From C116M (pin #42) to the disconnected dash plug C204 I read 623 ohms.
The circuit also goes to the Powertrain Control Module (PCM) C154 pin #41
which is causing the short circuit or 15A fuse to blow.

Although, I tried to find pin #41 on the PCM, I didn't know the proper ground to verify. Also checked the circuit from C154 #41 to C116M #42, read 1 ohm.

Is this a common or isolated Powertrain Control Module problem?

Can the PCM be repaired or replaced with a suitable substitute PCM?

I removed my unit and found the PN# F8UF-12A650-AAB is the correct unit for 1998 E-Series with 6.8L engine, I checked EBay and Amazon for prices, would it be better for me to purchase from the dealership?

Thanks, Mac

 

Hey Mac!

I don't have an EVTM for your year and that could cause me to give you bum info about testing the connector pins and their respective circuits, ground locations etc etc.

eBay etc are okay for new or salvage PCM's if they have a good return policy. I'd look for a local LKQ outlet because they're a very, very good outfit to deal with, at least in my experience.

Your questions about pins and circuits could be posted in the Electrical & Wiring forum---several who contribute there might have your year chassis EVTM and can give more specific info.

Sorry I can't be more helpful in this part.

 

I do have the manuals, but I'm having some difficulty figuring out which set applies to this particular vehicle. Econoline? F/B series? F150/250?

What are the first ten digits to the VIN? That should provide the accurate information.

Try this:

Disconnect clutch connector.
Disconnect the connector at the low pressure cycling switch
Measure the resistance from the Black/Yellow wire at the switch connector to ground, it should measure a high resistance.
If it measures zero, disconnect the PCM connector and re-measure. If it still shows a short, it's a wiring harness problem. If the reading goes to open-circuit, the PCM has an internal short on the input to pin 41.

 

I'd say you have a bare or pinched wire exposing the conductor to ground. Find that spot, repair an itshould be all good.

 

I found the PCM or ECU that inserts into the firewall was bad.

Talked to the Napa Auto Parts representative and ordered it back east for my particular application. It came with a mandatory Core Charge.

Installed into the RV and everything worked flawlessly, Air Cond Norm or Max Air, Heating and Defrost worked.

After all still had to get a new Air Conditioning evacuation and refill of refrigerant. Worked great.

Thanks for the help all,
Mac

 

What ECM was recommended---one for an F-Series or E-Series?

 

He has an E series RV, I'd assume it is for the E350 cab/chassis that the RV converter ordered.

 

Yes and I can assume the same thing but I'd rather hear from the OP as to what it actually is.

 

It was a E-Superduty RV conversion that was an ambulance pkg from Ford.

The ECU / PCM didn't need to get flashed according to the Napa Auto Parts Representative, he was ready to add the cost to flash the system with the newest downloads but wasn't required.

I'll look for the receipt for further info, not sure where I have it.
Mac