? for A/C Experts

[432bartman]

So our front A/C is not working. It has the Micro Air softs starts, which have been in place for approximately 4 years. I had a repair guy come out, who said the motor was getting very hot, and that it was possibly a bad motor. He had a motor which he installed and that was not the problem. He bypassed the soft start and used a regular start up capacitor, and the system started but ran very slow and would offer no difference in the hi speed fan setting. He is going to research it some more, but is stumped at this point, due to it not being a motor issue, a capacitor issue, or my soft start issue. What could be the problem if anyone knows. The entire system is getting the required voltage of 110. The rear A/C is running just fine, as we are on vacation in our Montana.

[432bartman]

Anybody?????

[Lee-CI]

What I know about A/C units would fit in a thimble with plenty of room left over. I seem to recall something about an unloader valve though having to do with relieving line pressure to prevent the compressor from stalling. What was the amperage draw with the new motor?

[DutchmenSport]

Just a question? Did the thermostat (inside the camper) check out OK? Was it tested to make sure it's not failing, especially since it won't change from high to low fan?

[rvman]

If the thermostat checks out then you are likely looking at replacing the control board in the A/C unit.

[Bourbon County]

I'm going to make an assumption that it's a Dometic unit? The reason I say that is because you referred to "the motor". Dometic uses a double shaft motor that drives both the evap and condenser fans, Coleman uses 2 smaller motors. The compressor motor is hermetically sealed inside a welded closed enclosure.

Does the compressor start and run at what appears to be correct speed? Is the problem entirely with the blower motor?

I've never installed one, but looking at the diagram for the soft start, it's only for the compressor motor. That makes sense because it's the only one that has much inrush current. There should still be a split type run capacitor with 3 terminals. One is labeled "C" which is common, another is labeled "Herm" which is for the hermetic compressor, and the other is labeled "Fan" which is you guessed it for the fan. was this capacitor replaced or at least tested? I think every single phase AC in the world uses one of these.

If the tech replaced the motor, I'm assuming (again) that he found no mechanical binding or rubbing that would pull the motor down? Did anyone put an ammeter on the fan motor and compare to nameplate data? That type motor with very long shafts isn't the ideal design; it puts a lot of stress on the bushings, but they seem to hold up pretty good. If he replaced the motor it would tell us that it isn't the bushings.

The different speeds are just different sets of windings in the motor, there's no electronic magic varying the speed; which set of windings gets energized determines the speed. I believe a couple of folks have mentioned thermostat and controller; that would be my guess if the other things have been cleared. The Dometic CT thermostats do have a history of failure, not sure which type you have.

The good news is everything in the fan circuit is pretty easily replaceable. A compressor problem or refrigerant leak is the death sentence.

[Reset19]

Our Dometic Blizzard NXT recently stopped working. The fan motor would turn slowly and the compressor sounded different. We have a Micro Air Soft Start.

There is a run capacitor (60/5 MFD in my case) that looks like a soda can that was bad. Everything worked after I replaced it. I got the replacement capacitor from Amazon. I was able to determine it was bad using the capacitor test feature on my multi meter.