Gremlins in the Coleman rooftop A/C voltage.

[puterbug]

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 first 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.

The j-box in the ceiling is model number 8330-3851 and the thermostat is 7330G3351 60277. The manual I was referring to can be found here, and I was following the steps on page 15 of it.

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 4 pictures 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!)

Any help is VERY much appreciated! Thanks!

[RV Wizard]

Hello puterbug and We are glad to have you join us here and we look forward to reading of your adventures and experiences. I am sure you will enjoy the website and forums. Good luck and keep us posted.
First off safety is the most important factor to keep in mind. Please only continue with troubleshooting if you are familar and comfortable with electricity and its safe guards.
From the pics you have posted, I can strongly recommend you upgrade the lower section of the 120 vac electrical distribution center. This is the converter/charging section that was supposed to recharge your batteries. This charging system was known for over charging batteries and could be producing dirty DC current which can interrupt electronic controls from functioning properly. On the cover should be the model number of the unit and RV Upgrades (sponsor of this website) can help you get the right upgrade.
If you check your battery bank you should have at least 12 volt dc output. If not you need to start here. Take the negative cable off and measure vdc. If you have 12 vdc reconnect cable and remeasure vdc. What do you find?
I tried to download the link you provide but was unable to at this time. I did go to RVP's site and looked up this http://www.rvcomfort.com/pdf_documents/1976376.pdf
As you can see if you go to the t'stat (that has 12vdc) and jumper the red to yellow terminals, the compressor relay should be energized. Red to Gh will be high fan and Red to GL is low speed fan. Re-check all of your control wiring at both the T'stat and roof unit control box. When you jumper the T'stat terminals, you should get 12 volts from ground to the yellow, green or gray at the ceiling junctions respectively.
Let me know what you find.

[puterbug]

Quote:

Originally Posted by RV Wizard Hello puterbug and We are glad to have you join us here and we look forward to reading of your adventures and experiences. I am sure you will enjoy the website and forums. Good luck and keep us posted.

Thanks! And thank you for your reply. I will be happy to share more of the story as I am planning some major mods to this little buggy.

Quote:

First off safety is the most important factor to keep in mind. Please only continue with troubleshooting if you are familar and comfortable with electricity and its safe guards.

I think I have free flowing electrons in my bloodstream, so I should be ok.

Quote:

From the pics you have posted, I can strongly recommend you upgrade the lower section of the 120 vac electrical distribution center. This is the converter/charging section that was supposed to recharge your batteries. This charging system was known for over charging batteries and could be producing dirty DC current which can interrupt electronic controls from functioning properly. On the cover should be the model number of the unit and RV Upgrades (sponsor of this website) can help you get the right upgrade.

Oh. The label. Duh. Nothing like overlooking the obvious. It is Magnetek Series 6300 A, Model 6332 Options: Q

Quote:

have at least 12 volt dc output. If not you need to start here. Take the negative cable off and measure vdc. If you have 12 vdc reconnect cable and remeasure vdc. What do you find?

Yeah I have 12.5 volts at the batteries AND at the converter.

Quote:

I tried to download the link you provide but was unable to at this time. I did go to RVP's site and looked up this http://www.rvcomfort.com/pdf_documents/1976376.pdf

Oh thanks, I couldn't remember where I originally found it, when I went back to the RVP site, I got lost in their links the second time.

Quote:

As you can see if you go to the t'stat (that has 12vdc) and jumper the red to yellow terminals, the compressor relay should be energized.

Quote:

Red to Gh will be high fan and Red to GL is low speed fan.

Oh, ok, more of the obvious. I had roughly 6.3 volts from red to blue last night. Ok. And roughly 6.3 volts from yellow to blue. Jumper them to add the voltages. Ok, I get it. That makes sense. So - - why is this Coleman thermostat not set up with a jumper in it? Geez!

Quote:

Re-check all of your control wiring at both the T'stat and roof unit control box. When you jumper the T'stat terminals, you should get 12 volts from ground to the yellow, green or gray at the ceiling junctions respectively. Let me know what you find.

Will do. I need to go up on the roof to do that, but I will return shortly (not sure if pun was intended or not lol) and let you know what I have up there.

I hate trying to squeeze into the ceiling to access that thing.

Thank you SO much for your very helpful and informative reply. I really appreciate it. Feeling hopeful... venturing back to the rooftop.

[puterbug]

Ok, I got 13 volts at Y and B up in the plenum.

I AM getting 120 volts to the box.

But, I am NOT getting 115 volts on the 1 & 3 pins (purple & yellow) to the compressor. Zip, zilch, nada. I tried jumping the freeze thermistor pins like they said in those steps on page 15, and that did not bring the compressor on either.

I did not yet attempt to bypass the compressor relay this time...

[puterbug]

Here was the clue. When I tested the voltage at the thermostat, it said 12.5 volts.

When I tested the voltage between Y and B in the plenum, 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 plenum.

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.

[RV Wizard]

Glad to hear you have gotten the problem corrected. Stay cool!

[puterbug]

Quote:

Originally Posted by RV Wizard Glad to hear you have gotten the problem corrected. Stay cool!

I work nights, and when I went to work, I clean forgot to set the thermostat temperature. I had it turned all the way down to 65. I normally keep it set at 80. I don't like it real cold.

So I walked into an icebox when I got home at 4 a.m. But without looking, I am guessing I got ice buildup upstairs on the roof. It's very humid, and cool, and foggy out and the unit was running, but struggling. Like the thermistor didn't kick it off, and maybe should have.

But here's the kicker. It also didn't shut off when I kicked the thermostat up to 80. I had it set on cool/auto. The fan kept running. So I set the fan setting to OFF and the compressor kept humming!

I turned it off at the breaker for now, and I am going to bed. I'm too tired to deal with it right now anyway, and need to get some sleep. If it needs to thaw out, well, it is cold enough in here right now anyway and it can just stay shut off for a while.

I am wondering if this new issue is related to that jumper on the red & yellow at the t-stat, which I left in place. I still have 12.7 volts there.

What do you think?

[puterbug]

Ok I haven't had coffee yet, but I went ahead and undid the jumper and the thermostat now seems to be acting as it should.

[RV Wizard]

Correct; you do not want the jumper in place. The compressor will continue to be energized as you found out.

[puterbug]

That little success only lasted a few minutes. The recently rebuilt fan motor died another screaming death. The guy who rebuilt it for me is going to give me credit for that cost toward a new fan motor. He didn't even seem surprised that it didn't last long.

I am just hoping the dying fan motor didn't blast the fan relay in the j-box when it went out this time. (That is what happened to the first of the three j-boxes.)

Although, I suppose it wouldn't have damaged the j-box, SINCE I HAVE A SPARE J-BOX NOW. It would only fry the j-box if I did NOT have a spare j-box on hand, right?