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rear dometic fan

May 23, 2013, 07:26:35 pm

guys the rear fan on our 99 u320 just stopped working, it spins freely, the compressor kicks on, but the fan does not run.....ideas please......tried using the comfort contol in the fan setting but it does not run in any function.....

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Re: rear dometic fan

Reply #1 – May 23, 2013, 07:56:24 pm

Hi Dave,

If all fans won't run when requested, it may be your thermostat. The thermostat can be tested to make that determination. You might call or send a private email to me frerichs@rcom-ne.com to get more details. If only one fan does not run, then it's probably the thermostat, wiring, connections, fuses or most likely... the fan itself. If you can get to a fan in question, try applying 12 VDC to it.

Jim

2002 U320

308-440-5154

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Re: rear dometic fan

Reply #2 – May 23, 2013, 09:33:32 pm

so far, it is just the rear fan, front works fine, compressor comes on in the rear, but the fan does not run, so i assume the thermostat is sending a signal,  tried spinning the fan with the power on at the thermostat, and it still did not start, although it spins freely.....will try applying 12 volts tomorrow, but where does it have to be applied, seeing  that it needs a capacitor to start?

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Re: rear dometic fan

Reply #3 – May 23, 2013, 09:57:34 pm

The fan motor for the rear ac is a 120 volt ac motor. It could have a bad fan motor or also have a bad capacitor. You can check on the pc board in the ac after removing the outside shroud and the metal caver over the pc board and see if the wire to the fan motor has 120 volts on it when the thermostat is turned to fan only

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Re: rear dometic fan

Reply #4 – May 24, 2013, 10:35:59 am

Dave,

Oh, you are asking about the air conditioner fan! I misunderstood - thinking it was the fan for heat at the floor.

For the A/C fan, check to see if you have 120 volts coming from the A/C control board to the fan. If not, then the wires for the fan may be unplugged or the relay is bad. If you do have 120 volts power from the A/C board, then suspect the start capacitor and the motor. When the compressor runs but not the fan, the unit will freeze up and probably shut down if it has freeze sensor.

Sorry for the initial confusion,

Jim

2002 U320

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Re: rear dometic fan

Reply #5 – May 24, 2013, 03:42:03 pm

can anyone explain where to check for voltage..i have the cover off, and there are five wires going to the fan motor...so far i hear the run capacitor may be the issue, and that if it is the board, i have to replace both boards and install a new thermostat, since parts are not available.....

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Re: rear dometic fan

Reply #6 – May 24, 2013, 05:24:32 pm

Dave,

On the A/C board I test all thermostats on (#3106482.015, which probably was used for may years with the four button Comfort Control Center) the output colors labeled on the board for the fan are: (not related to wire colors)

low - red

med- yellow

high - black

auto - violet

You should check for continuity from the incoming neutral to the fan neutral - all power off for safety.  Obviously an open 120 volt neutral to the fan would stop normal fan operation. Wouldn't it be simple if this is your problem.

With the120 VAC on logically the start relay would be engaged for starting all three fan speeds. Placing one of your AC volt meter probes on the incoming neutral and then the other probe progressively on each fan speed output pin should show each of the 120 VAC outputs to the fan. If the fan rotates slowly and doesn't come up to speed or just hums, it may be just the start relay that is bad. No rotation or hum, it might be a bad motor. No voltage on the board's fan pins may be bad relays coils or their contacts.

The middle position large relay (K1) is for the compressor and the outside position large relay (K2) is for heat strips.

If your board is the same number, I have some replacement AC boards so upgrading to a 5 button system should not be necessary. Should your thermostat be the problem (doubtful if the display shows all the fan speeds when selected), I have those also.  If Dometic does not support these air conditioners with parts any longer (give them a call), a motor shop should be able to find a replacement motor or capacitor for you.

Jim

2002 U320

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Re: rear dometic fan

Reply #7 – May 24, 2013, 05:42:11 pm

Oops, slight correction:

start "capacitor" not start relay.

Jim

2002 320

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Re: rear dometic fan

Reply #8 – July 13, 2013, 10:45:43 am

Mine did the same thing. I found that the dual run capacitor the fan said was bad. I put two in it's place. Fan is 10
Microfarad 370v and compressor is 20micro. Runs gt
Runs great.

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