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Thurman 09-03-2012 12:27 PM

Help with A/C and thermostat wiring
To set things up: I have a 2005 FR Grand Surveyor with a Dometic 57915.331 A/C unit that uses a thermostat on the wall. A couple of months ago the unit stopped cooling at all. Upon inspection we, my electrician friend and I, found a pin-hole in one of the condenser tubes, therefore no freon. I ordered what was to be a direct replacement unit model 457915.331 and installed this unit. The new unit has one major problem, to me: It is controlled by the knobs on the unit itself which means that it runs continuously with the compressor kicking in and out as needed. The seller insured me that I could just change out the electrical control box on these units and the new unit would run off of the thermostat. NOT ! We drew detailed wiring diagrams before taking the old unit off. We have it wired exactly as the old one was wired but nothing happens when the thermostat is switched to cool, nor does the fan run when switched to "ON". We put the old "faceplate" back on the new unit and it runs fine, so it's not the unit. We've pretty well reached a dead end here so I'm asking for help. PLEASE do not recommend the only local RV repair center, just not a good place to do business with. I have photos and wiring diagrams but don't know what to post at this time. Thanks, David

Herk7769 09-04-2012 07:27 AM

You said "the seller" so I assume you bought it from someone other than the manufacturer of the bad unit.

Did you buy it direct from Dometic? Their Tech department can help.

Did you buy it online? Maybe their tech department can help.

If you bought it 3rd party (used) perhaps it is bad?

"Attach" using the paperclip icon any JPG or GIF files you have of the OLD wiring and any of the new wiring. We can try to help.

Thurman 09-04-2012 03:31 PM

The "seller" was RV Country in Tennessee, and the unit was brand spanking new. The person I talked to at RV Country about swapping the electrical controls so that the new one would run off of the wall thermostat told me that it was only a matter of matching up the T-stat wiring. Both units have identical six-wire plugs on the unit themselves. I am going to take photos and will post them ASAP. Thanks for the reply, David

Thurman 09-06-2012 10:56 PM

Excuse me, the seller was "RV Parts Country". They were very helpful before the sale. One of their tech people told me that the replacement unit would indeed work with the Hunter digital thermostat the old unit had been working with. All I should have to do was to change the mounting plate from the old unit to the new one, and change the electrical control box (with PC board) to the new unit. I did chart the wiring before I removed the old unit and every wire was put back where it should go, but the new unit will not operate with the Hunter thermostat. The new unit will operate with the supplied control panel-not what I want. I have seven (7) photos to upload, should I just add them to a "reply" or is there a way to link a file? Thanks, David

Witch Doctor 09-07-2012 04:05 AM

I think it would be best to post them the site so we can see them, I use to do HVAC and I know that their is another guy that also did HVAC repair. It could be tricky, but did you get a wiring diagram with the unit? Also I agree with Herk the hotline should be able to help you. I would call them also. I have never heard of switching from a self contained knob unit to a thermostat. BECAREFUL you could blow the PC board...........:thumbsup:

cfsoistman 09-07-2012 06:01 AM

Here's the installation instructions with some control wiring info included. I wonder if the new control package which matches up with the new digital Dometic T-stats might not be compatible with the Hunter since the Hunter replaced an old analog t-stat. It might be a better choice to get a Dometic t-stat to match up to the new AC Unit.

Hunter 4299B Digital Thermostat RV Installation
Here's the Hunter set-up for the replacement of the old analog t-stat.

Witch Doctor 09-07-2012 10:32 AM

Did you get a CCC system with the unit? Plus just to be sure this is not a heat pump system correct?

Thurman 09-07-2012 10:48 AM

No, I did not get a CCC unit for this package, there is NO heat pump in either the old unit nor the new one. YES, I did get a wiring diagram with the new unit and it is identical to the one for the old unit. One call to Dometic and we agreed that I would take photos of the old unit as removed, the new unit as mounted, the Hunter thermostat that had been working quite well with the old unit after replacing the old Duo-Therm unit. I am to send them to them so they could view them, and maybe find an answer to this problem. I'll upload the photo's ot this fourm after getting home this afternoon. The only visible difference between the two units when looking up from the bottom is that the old unit has the two black wires for the freeze control hanging down along with the six-wire connector. I changed the freeze control over to the new unit exactly as it was positioned on the old unit, clamped to one of the 180 bends on the evaporator. I'm seriously beginning to suspect the control board. or maybe this old man's eyes and thinker are not working so well right now. Thanks to all for the replies, David.

Thurman 09-07-2012 02:07 PM

5 Attachment(s)
Not the best way to do this, but: Attachment 19234

Attachment 19235

Attachment 19236

Attachment 19237

Attachment 19238

Thurman 09-20-2012 07:16 PM

1 Attachment(s)
Should have posted this sooner, but: In photo #5 within the lower left-had quadrant you can see the front of the control board withing the electrical box housing. What you cannot see is the back of the printed circuit board, nor could I until I removed it from the electrical box. I think this photo will explain the cause of all my problems. The circuit board was actually this way when I bought the camper eleven (11) months ago. Two copper traces have been "jumped", and one solder joint had an attempted repair burning out the solder pad for the resistor. The A/C had worked just fine until June when the hole came in the condenser tubing. Maybe bumping the circuit board around when changing out the units finished it off. Anyway, new board and all is working just fine.

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