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Electrical Discussion of preventative/corrective maintenance and other technical issues regarding your coach's electrical system.

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  #1  
Old 03-29-2019
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Default Roof AC Power Fluctuation

The Front AC on my coach has started acting up. The thermostat lights will flicker, then the low power will blink, then the unit resets. I'm on pedestal power and have a 50 AMP autoformer (in theory should handle power sags). I have confirmed that the problem happens on generator as well - it even makes the generator stumble for a second when it happens.

I haven't checked the contactors yet, but I have always had a little buzzing coming from the closet so I'm thinking that the contactors may be issue. What I don't know is how to actually test the contactors? Or do you think that I should be looking for the problem somewhere else?


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Old 03-29-2019
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Quote:
Originally Posted by Kiwi3 View Post
The Front AC on my coach has started acting up. The thermostat lights will flicker, then the low power will blink, then the unit resets. I'm on pedestal power and have a 50 AMP autoformer (in theory should handle power sags). I have confirmed that the problem happens on generator as well - it even makes the generator stumble for a second when it happens.

I haven't checked the contactors yet, but I have always had a little buzzing coming from the closet so I'm thinking that the contactors may be issue. What I don't know is how to actually test the contactors? Or do you think that I should be looking for the problem somewhere else?
Since it’s pretty easy, I think I would first try a thermostat from a working AC unit just to make sure you don’t have a bad thermostat.

Next I would probably check voltage on the output of the relay that supplies power to the front AC. My AC relays are under the carpeted floor of the mirrored closet that goes across the back of our 91 WB - not sure where yours are.

If the power is stable on the output of the relay, you might want to go up on the roof and check the pc board, relays, connections (including the compressor terminals), etc. up there

Loading down the generator could possibly be a sign of a capacitor problem on the roof top unit causing excess starting current.
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  #3  
Old 03-29-2019
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My guess is bad compressor
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Old 03-29-2019
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My guess is bad compressor



x2


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  #5  
Old 03-29-2019
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I agree it is prob compressor start. Watch the ac amp meter when the fan and then compressor kicks on. The reaction should be the same as the average of the other two as a base. Check the transfer switch especially the neutral wire jacket for heat issues and compramise. Harbor freight has clamp on amp meters at a reasonable price you could use one ontop to check amp drag. While ontop, have a look at the capacitors and a look at the heating elements to make sure they are not turning on at the same time.
Note that not every clamp on amp reader does dc amps. Even if the meter reads dc amps you need to check if the clampon feature is ac dc.
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Old 03-29-2019
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Not really what I was hoping to hear, but it is 25 years old.
So your thinking the compressor itself, not the compressor start capacitor right?
I did try swapping the start capacitors from a different unit and there was no change. I'll have to check the AC AMP draw, need a clamp meter.
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Old 03-30-2019
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Well today I started the troubleshooting John suggested.
Yeah, I should always do that.
The thermostat is goofy. Swapped with my rear thermostat and it runs like a champ. So now I'm in the market for a Dometic Duo-Therm Thermostat for an electronic control. I pulled the circuit board to check for any loose connections but it looks solid
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  #8  
Old 03-30-2019
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Is itone control thermostat for all 3 ac's. And doesit use dip addresses and pbome cable clips?
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Old 03-30-2019
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Nope I have a separate thermostat for each AC.
Looks like part# 3101625.014 model# 5054

Quick internet search and it looks like they are rare now.
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  #10  
Old 03-30-2019
GregOC GregOC is offline
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Not sure what parts are muffed. if you put the old t-stat in the back and it does not work that may prove completely. some time moving those things around causes intermittent issues.

If you have phone cable snap cables, keep in mind the female couplings are reversing or passing. and the wires colors are also reversing or passing.



this guy is worth giving a phone call to I sent him a 4 button controller to fix and he sent it back saying there is an issue some place else. Nice guy

https://www.williamhendrix.com/About-Us.html
Dometic customer service is also very helpful and responsive on the phone.


I replaced a rear ac because it had a hard start kit on it. new unit was worth the investment because startup and efficiency is better. I can run the rear ac for 6 hours on the inverter, problem is the lxi have a common exhaust duct so it ends up cooling down the entire rig I was thinking of installing a baffle but now looking for a rig with 4 ac's and Girrards
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