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Dometic Rooftop Heat pump is tripping AC breaker

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My four year old Dometic Rooftop Heat pump is tripping the AC breaker. I can re-set the breaker and it will stay set until the thermostat calls for either cooling or heat. Up on the roof I can see the fan does not attempt to start nor does the compressor. I hear a very faint click and then the breaker trips. The fan spins freely and I can set the thermostat to just "Fan" and that does work. I cannot smell any kind of burning nor do I see and damage to any wires. I am thinking start capacitor either fan or compressor.

Edited by Mikescamping

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To really trouble shoot the problem you need a clamp on ammeter. If I were to guess based on what little we know I probably would try the start capacitor. 

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The order in which I would troubleshoot is:

 1) Get an ammeter to try and get a read (to whatever extent possible ????) on the amps its pulling when trying to start the compressor….

 2) If NOT off the charts, try substituting another breaker just in case the old one is defective. 

 3) If a new one trips and the initial starting current is excessive, try a new start capacitor.

 4) If that doesn't help and the initial current draw remans excessive and a "correct sized" breaker still trips, take two aspirins and call me at the office Monday lol

   Other possibilities if its NOT a breaker or start capacitor or compressor problem,  may be the branch circuit FROM the panelboard TO the unit causing excess line voltage drop due to a faulty/loose resistive wiring connection.

   NOTE I don't know what sort of contactor or start relay etc etc the unit may have ???? If it had burned resistive arcing contacts and was dropping excess voltage THAT COULD BE A PROBLEM     

 If you had a voltmeter right where the wires connect to the unit (and/or to the in and out of any relay/contactor per the note above) and try to start it, that can disclose excess line voltage drop from perhaps a faulty/loose/resistive connection from panel to unit. ALSO insure there's sufficient voltage TO the panel itself and the parks pedestal as low voltage or a faulty connection or excess line voltage drop anywhere causing low voltage to the unit can cause problems.

 Ammeter,,,,,,,,,Voltmeter,,,,,,,,,Breaker,,,,,,,,Capacitor may help, but if voltage and capacitor and breaker are alllllllllll good yet she fails to start and trips ????????? Compressor ????????????

 

John T  NOT any HVAC expert, so hopefully someone electrically familiar with your unit can better answer your question 

Live from Walmart in Bartow Florida

 

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To isolate the problem try running the fan by itself, you can do that from the thermostat. If it runs then switch it to a/c or heatpump and see what happens. If it snaps off instantly then the compressor is shorted out internally. To confirm that take the cover off the compressor terminals and disconnect all three wires and take your multimeter set it on ohms and see if you have continuity between the terminals and the copper lines, if you do it's grounded and it's bad.

Denny 

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I have had two compressor fans go out on our newest dometic heat pump. Didn't fix last time and quit uaing it and going with mini splits, Anyway fan both times turned free with my hand. Turn unit on with cover off and fan starts to turn and lock up. If left on would trip breaker. Fan motor bad. jfyi

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I vote for old John's #3 comment. If the start and run caps test good, move to his next suggestion.  re: that fan, if you can feel ANY sideways movement in the shaft, the bushing is shot. This allows the armature to contact the windings = new motor.

 

Edited by Ray,IN

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I experienced this exact issue with my heat pump in October. My DW said repair or replace. I ended up installing a hard start capacitor and no more problems. It was cheap on amazon.

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36 minutes ago, Mikescamping said:

I have ordered the hard start and the original start cap and will hope it fires up. 

 

Did you check the unit for grounds before you ordered parts.

Denny 

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10 hours ago, Mikescamping said:

I have ordered the hard start and the original start cap and will hope it fires up. 

In my 30+ years as a tech, a circuit breaker failing is very unusual and what you have told us indicates that this was pretty sudden. It wouldn't hurt to try swapping it with another if you have 2 that are the same rating, but I wouldn't hold much likelihood of that doing anything for you. Did you do the compressor check suggested by Denny? If you did verify voltages and make sure there was no short to direct ground, there is a good probability that it will prove to be a capacitor since that is one of the more common problems with RV air conditioners.  Part of the problem is that most of us have very little air conditioning troubleshooting experience, even though we may have worked on RVs for years. That is partly because RV air conditioners don't usually give much problem and most of us don't have access to very much technical information or schematics for them. If you check with Bryant RV Service website, he does have 1 Dometic heat pump service manual posted there. I suggest that you visit and download a copy as it may prove to be quite helpful. On pages 81 & 82 the troubleshooting addresses what seems to be your problem.

Another YouTube that may help is in this link.

Edited by Kirk W

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Mike, trying a new start capacitor is a good plan as its not all that expensive and ifffffffffff its not a circuit breaker (I saw several failures over my engineering career and 49 years of RV ownership) or a relay/contactor problem, or low voltage, or a faulty circuit, or a bad compressor, that may well prove to have been the problem all along FINGERS CROSSED ???? The current and voltage checks I recommended might still provide answers. 

A soft start unit is a good item to have REGARDLESS. HOWEVER, your original problem of tripping the breaker still needs cured. Even if a soft start allows it to work you still need to find the cause of excess starting current if ??????????? it remains. In the event the start capacitor was the problem all along then you now have that cured plus the soft start unit is a great addition.

 You're gonna get this

Merry Christmas

John T   headed to Avon Park Florida

 

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1 hour ago, Mikescamping said:

Yes this is my video. 

 

 

I should has added to my post before you did your test, I  should of had you check between the posts C to R, C to S. To make sure you have continuity between them.

Does your unit already have a start cap, it should be smaller and black or white. If it does there will be a small hollow in the top, see if its soft or bulged out. If it is its bad. If you bought a hard start kit be sure to remove all the old start cap and relay before installing the new one but keep the parts so when the one size fits all kit fails your will know the correct parts to get to get back to factory specs.

Denny 

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make sure the unit is clean also, over the years they can get quite dirty, filled with all kinds of things, I would start with the breaker first,if it has any kind of arcing that you can see 

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7 hours ago, Mikescamping said:

Hey Denny,

A video is worth a thousand words so let me know what you think.

 

It gives a idea what you are looking at and if you noticed he didn't check for a ground. The ohms between the common terminal and start and common to run terminal equal the ohms between the R ans S terminal so the windings should be good but if you don't have the factory specs its a guess. On the black start cap you can see the white spot on the top of the cap thats where it will bulge if if it's bad he didn't show the start relay device that takes the start cap out of the circuit. 

I worked on so many units of all kinds comercial and residential I knew where to start looking just by the sound and what it was doing. If it triped the breaker the first thing I checked was for grounds, if the compressor started but trip the overload shortly after startup the start relay was bad, if it wouldn't start then the start cap and run cap. If everything checked out then the compressor was locked up. I did it so many times it was a matter of few minutes do diagnose the problem now that I'm old and out of practice it you take a little longer. You need a good clamp on amp meter to do a lot of the test.

Denny 

 

 

 

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Thanks again Denny,

I did check for ground on each terminal and found no short to ground so I am thinking the problem is not the compressor.  I think that the starter relay is located on the control board. If the control board is bad I think I will have to replace the entire board. I could not see where I could remove any of the relays. Per your response I will also order a start cap. I have already ordered the run cap and a hard start cap. If it turns out to be the control board I might be able to use new capacitors down the road. I have two heat pumps on our rig. Again Thanks so much for all your help. Merry Christmas!

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