Duo Therm A/C Troubleshooting - non op fan

[FloridaFlyer86]

Model 57915.741 Dometic A/C
3107610.002 thermostat?

After about 5 weeks of non use in the Florida heat, tried to turn on A/C, compressor ran but not fan- selected fan from "auto" to "on" and blew the 3 amp fuse on the control board. Tried it again and same result... bad board? I've checked there are no critter nests obstructing the fan... of course this happens 4th of july weekend - and I'm not trying to have a vacation, I'm a full timer. (not sure which would be more frustrating haha)

[marcsbigfoot20b]

j-d wrote:

eHoefler wrote:
The capacitor is for the compressor, not the fan. Chances are the fan has a bad bearing and is not spinning freely.

Untrue and True!

Untrue: The FAN does use a Capacitor. It's a RUN Capacitor only. Compressor uses a RUN Capacitor as well, and in addition it MAY have a START Capacitor.

So, Always RUN Capacitors, for BOTH "motors" (Fan and Compressor). Some A/C's use two separate Capacitors, but many such appliances use a Two-in-One Capacitor. Usually around 05 mfd for Fan and about 35 mfd for Compressor. Easy to tell. The two-in-one will have three sets of connections. Singles will have only tow per capacitor.

Then IF there's a Start Capacitor, it is connected across ONLY the Compressor Capacitor (or that part of a two-in-one).

TRUE: Heartily agree the Fan Motor Bearings could be sticky, so the idea of rolling it over by hand to check, is a very good one. Those fan motors have very, very, little starting torque. Doesn't take much to keep them from being able to spin up.

If everyone answered incorrect replies like this and supplied the correct info in a classy manner like you did, this forum would be so much more pleasant. Thanks.

[joebedford]

On my old rig, if the air conditioner had been sitting for a few weeks without use, I had to push the squirrel fan with a stick to get it moving. Then it would work just fine until the next period of disuse.

[dougrainer]

The Boards 3 amp fuse has NOTHING to do with the 120 operation of the fan or the compressor. It is a 12 VOLT protection. That means there is something on the BOARD or the tstat wiring that is blowing the fuse. I would pull the Tstat and check the Wire Bundle and tghen check the wiring at the upper control box. I cannot remember when I ever had a problem with the Board 3 amp fuse blowing. Usually if you have a short, it is pretty obvious. Also, if the 3 amp fuse blows, does the COMPRESSOR stay ON? Doug

[FloridaFlyer86]

I knew I should have checked that before, but nope, fan spins completely free, spins for several seconds on its own. I tried again in case the brushes were on a bad spot, but same result, another blown 3 amp board fuse. It might be worth mentioning that i've been experiencing multiple seemingly unrelated problems since coming home, and I'm starting to wonder if there was a lightning strike here while I was gone - the WFCO 8900 converter is dead (I know they're junk but still) a blue sea low voltage disconnect is apparently dead, and a IOTA 15 amp charger is non op. I wouldn't think that a strike would cause that much trouble, but I don't know why else so much equipment is dead after just a few weeks of non use...

[j-d]

eHoefler wrote:
The capacitor is for the compressor, not the fan. Chances are the fan has a bad bearing and is not spinning freely.

Untrue and True!

Untrue: The FAN does use a Capacitor. It's a RUN Capacitor only. Compressor uses a RUN Capacitor as well, and in addition it MAY have a START Capacitor.

So, Always RUN Capacitors, for BOTH "motors" (Fan and Compressor). Some A/C's use two separate Capacitors, but many such appliances use a Two-in-One Capacitor. Usually around 05 mfd for Fan and about 35 mfd for Compressor. Easy to tell. The two-in-one will have three sets of connections. Singles will have only tow per capacitor.

Then IF there's a Start Capacitor, it is connected across ONLY the Compressor Capacitor (or that part of a two-in-one).

TRUE: Heartily agree the Fan Motor Bearings could be sticky, so the idea of rolling it over by hand to check, is a very good one. Those fan motors have very, very, little starting torque. Doesn't take much to keep them from being able to spin up.

[eHoefler]

The capacitor is for the compressor, not the fan. Chances are the fan has a bad bearing and is not spinning freely. You could try and oil it and see if you can spin it by hand to free it up to get you by, but most likely the fan motor needs to be replaced.

[DinTulsa]

Does anyone know what capicator a Duo-therm 15k unit would use?

[j-d]

When you checked FAN for obstructions, did it spin freely?

Wild guess, but IF the FAN Capacitor (or the Fan half of a two-way capacitor) is bad, then the fan motor can't start and its AMP draw goes to a Locked Rotor value instead of a Running draw.

Got another Capacitor, or one you can swap from another A/C, or a meter that reads out Capacitance?