SOLVED: Gremlins in my Coleman rooftop a/c. A voltage question.

I have a 2000 Winnebago 27P Class C and I am hoping someone can help because I am at my wits end trying to figure out the gremlins that are plaguing my rooftop Coleman air conditioner.  It will be a while before I can take the rig to ANY shop, but I can follow diagrams and directions, and I am hoping someone can help me get this solved. 

After very carefully following the RVP troubleshooting guide, I recently replaced the control box in the ceiling and the thermostat and had the fan motor rebuilt. 

It turned out the compressor relay in the new j-box was bad, so I went and got yet another one.  (When I bypassed the relay, the compressor kicked on.)

Now with this THIRD j-box, I am NOT getting 115 volts on the 1 & 3 pins to the compressor.  AND I am only getting 6 volts to the red & blue (DC-) and red & yellow (fan) wires on the thermostat.  RVP says it should be 12 volts.  And...those wires were getting 12 volts when the old thermostat was in place, so what the heck could have happened that now I am only getting 6 volts?

Beyond that RVP says only "restore 12 volts to the thermostat".  Well ok.  But how the heck do I do that?  I was going to try to trace the wires down the wall from the thermostat, but they are really anchored in there somehow.  They definitely go DOWN the wall, so I was hoping they would emerge at floor level somewhere, and lead me to the 12 volt power source, but I can't find them anywhere.

And... where the heck is my inverter/converter or whatever it is?  I thought it should be under the refrigerator near the power panel with the circuit breakers, but I have no clue if it is or not.  I have attached a picture of what I found there.  What is it?  (Besides dirty? - - and I am afraid to reach in there to clean it!  It is also very hot to the touch!) 

EDIT:

I guess that IS the converter.  It is putting 12.5 volts to appropriate places, like to the fuse panel next to the circuit breakers.  But where did the other 6 volts wander off to on their way to the thermostat?

Oftentimes the voltage for the Thermostat comes from the Control Board in the A/C.

Yeah - that looks like your converter.

What is your model (Suncruiser, Adventurer, or what?)  I'll try to look at your wiring diagrams later this morning.

It's a 2000 Winnebago Class C Model 27P.  Minnie?  Minnie Winnie?  Something like that...  on a 1999 Ford chassis.  I hope that helps.  I got a caseload of manuals when I bought this thing, but nothing like a wiring diagram.

I jumpered the red and yellow connections at the thermostat to get 12.5 volts.  That is the fan and compressor DC power.  Each lead was getting 6.3 volts by itself.

This jumper gave me 12.5 volts.

But I still did not have 115 volts a/c at the 1 & 3 pins on the j-box!  I tried jumping the freeze thermistor.  Nada.

Then Saint OBVIOUS slapped me upside the head.

When I tested the voltage between Y and B at the j-box, it said - 13 volts. MINUS. Now on my little voltmeter, a minus sign means you have the polarity reversed on the leads. I admit, I sometimes go willy nilly with those leads when I am testing - - and don't really pay attention to plus or minus. But OBVIOUS knocked me upside the head for the third time today.

So...EVEN THOUGH I had marked the wires when I took them off the ORIGINAL plenum (which had been installed three or four years ago by an RV technician btw...) I went ahead and reversed the Y and B leads to the j-box.

VOILA I magically had 115 volts to the 1 & 3 pins.

NOW I haz cold air coming. 

Just to check it, I re-installed the j-box that I accused of having a bad compressor relay. Yep, it works too. I guess I will tuck the spare j-box away for a rainy day. I only went $66.00 and 60 miles out of my way for this error this time, but days and days of frustration and way too many trips up that ladder testing and swapping.

However, the dogs are now pleased and have decided to let me continue to live here, at least for a little while longer.

puterbug said:

Now on my little voltmeter, a minus sign means you have the polarity reversed on the leads.

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One of the benefits of an analog meter - when the needle slams over to the left, you have the leads reversed  ;D  I must say I always have to stop and think a bit when metering DC with my Fluke DMM.  Sometimes I wish I was using an analog meter.

Thanks for reporting back!!  Now I can go watch football and not look at your wiring diagrams 

puterbug said:

It's a 2000 Winnebago Class C Model 27P.  Minnie?  Minnie Winnie?  Something like that...  on a 1999 Ford chassis.  I hope that helps.  I got a caseload of manuals when I bought this thing, but nothing like a wiring diagram.

Click to expand...

If you go here http://www.winnebagoind.com/resources/manuals/ on Winnebago's web site you'll find full parts, wiring, and plumbing diagrams for your rig.

cbeierl said:

If you go here http://www.winnebagoind.com/resources/manuals/ on Winnebago's web site you'll find full parts, wiring, and plumbing diagrams for your rig.

Click to expand...

Oh!  Cool!  Thank you!

I just wanted to say thanks to the fellow who put up the link to Winnebago's service information. That is a goldmine.

eflester said:

I just wanted to say thanks to the fellow who put up the link to Winnebago's service information. That is a goldmine.

Click to expand...

Lots of good stuff in the Winnebago Resources post near the top of this board!