Dometic A/C Capacitors ?

[41magnum]

YES!..the run cap with the built in resisitor helped!
BUT, now it trips the breaker at the house.
No smoke anywhere.
My electical buddy says that means its the compressor.
My repair friend did not put his ohm meter on it, though.

Should I just order a compressor?

thanx

Trapper John

[41magnum]

Richie says he put the ohm meter on the compressor and it looks good.
This hookup, thru a regular 110 outlet in our granary bldg ran that a/c fine last summer.
Is is possible, if another camper a/c was running at the same time, on our Jayco, that THAT would trip the breaker since all our outbuildings MIGHT come off the same breaker???

[MrMark52]

Originally Posted by 41magnum

YES!..the run cap with the built in resisitor helped!
BUT, now it trips the breaker at the house.
No smoke anywhere.
My electical buddy says that means its the compressor.
My repair friend did not put his ohm meter on it, though.

Should I just order a compressor?

thanx

Trapper John

I'm confused - it appears to me from the pictures you have two capacitors, with one of them being a 3 terminals device in a metal can. The metal can was previously noted to have a hole in it.
Next to it, was a plastic cased PTCR capacitor that had a horribly burned top. That capacitor is typically referred to as a "soft start" capacitor, solely for the compressor.


With the run capacitor getting a hole in it, it spilled all it's cooling oil. And if the compressor ran with the capacitor in that condition, it could very well cook the compressor windings. And is why I said to measure the resistance of the compressor windings before proceeding to insure they are not internally burned together or shorted to ground.


Understanding how all this goes together depends on what capacitors you get, start and/or run.


The run capacitor you have is really 2 capacitors - a fan run and a compressor run. You can get an exact replacement, or you can get 2 separate capacitors.
If you get an exact replacement, then hook it up just like it was connected.
If you get 2 capacitors, then you will need to jumper a wire to the wire that is on the "C" terminal of the 3 terminal cap, to the terminal with a line on it of the 2 terminal capacitor. The other end of that wire will connect to the "C" terminal (again, terminal with a bar or mark on it) to the fan run capacitor.


For the new soft start capacitor, you connect it across the 2 terminals for the compressor run capacitor.


Pictures of the capacitors that you get, plus better pictures of the actual terminal end of the 3 terminal capacitor with the wires connected would help so I could better explain.

[MrMark52]

Originally Posted by 41magnum

Richie says he put the ohm meter on the compressor and it looks good.


That's comforting - but it would really be nice to know what readings he got between all the points i described.







This hookup, thru a regular 110 outlet in our granary bldg ran that a/c fine last summer.


And that was before everything burned up.





Is is possible, if another camper a/c was running at the same time, on our Jayco, that THAT would trip the breaker since all our outbuildings MIGHT come off the same breaker???

It's possible that the two a/c units combined pull too much current for the single breaker. If both units pull 15 amps full load, and you've got it on a 20 amp breaker, then the breaker will trip.
But what caused the burned capacitors in all liklihood was not caused by 2 a/c units on the same circuit. What you have was either a lightening strike or a wire shorting to ground for some reason (broken, worn insulation, etc.).


I bet if you turn off the other unit, that this unit will still trip the breaker.


Any electrician worth his $ will understand the issues of too much load on a circuit. Some will understand how PSC (permanent split capacitor) motors work, as well as how PTCR (soft start) capacitors work as well as how to hook them up, and/or measure their resistance to determine if the motor part of the compressor or fan is good.

[41magnum]

i need to clarify...…
Richie ohmed the compressor and says its good.
the fan works properly.
He got it to run and push cold air but not for more than 5-10 mins before the breaker tripped at the house.

He texted me late last night, saying the 2 campers are on SEPERATE breakers at the house.

[MrMark52]

Originally Posted by 41magnum

i need to clarify...…
Richie ohmed the compressor and says its good.
the fan works properly.
He got it to run and push cold air but not for more than 5-10 mins before the breaker tripped at the house.

He texted me late last night, saying the 2 campers are on SEPERATE breakers at the house.

OK -


Now we need to know how much current the a/c unit is pulling wile running, and at the same time we need to know the voltage at the unit.


Answers to the above will give insight into what is causing the breaker to trip.


Alternatively, how long is the cord from the a/c unit to the breaker panel, what wire size is the cord, and what size is the breaker?


If the cord length and size is correct for the circuit then we need to know specifically how much current the compressor and fan are pulling, and comparing those readings to what they are supposed to pull. And, confirming that while the fan is running, is it running design speed?


One final indicator of under-voltage or improper cord sizing is to grab the cord while the a/c is running. If it's anywhere from warm to hot, then it suggests the cord is not sized right, is too long, or you've got an under-voltage issue caused by an undersized electrical component somewhere in your electrical service. Pay close attention to the cord caps on all cords for signs of heating. At most you should only feel a slight hint of warmth on any current carrying cord or associated component.


But getting actual voltage and current readings at the a/c unit with it running will tell us if it's a power supply issue or internal to the a/c (compressor or fan motor).


This also assumes you hooked up the new capacitors exactly as they were on the old burned up capacitors (if you got the compressor hooked to the portion of the capacitor that was intended for the fan motor, and vice versa. I doubt the fan motor would start on it's own then, but stranger things have happened - and with the soft start on the compressor, it would likely start/run with the wrong capacitor hooked to it).

[Fkrel]

If it was mine I would replace the complete unit It's not worth the chance of waking up and trying to find a way out of the motorhome thats on fire. Anything that would melt a metal cap that bad would make me stay awake at night worrying about it.

[41magnum]

""how long is the cord from the a/c unit to the breaker panel, what wire size is the cord, and what size is the breaker?""

2 heavy black R/V cords from Camping World with 2 blades and 1 pin. I think they are 50 ft each...THEN its 50 yds to the house from outlet the lil yellow adapter is plugged into.

This set up ran FINE all last summer, I should add.

Breaker is 15 amp.

Lightning strike is a possibility since we don't live at that place much.

[MrMark52]

Oh, jeez - with that much cord I would be surprised if the unit is even seeing 100 volts and am surprised it even runs.


I don't know which 50 foot cord your speaking of from Camping World so I don't know what wires size is being used. If you look at the side of the cord it will have printed or embossed on it the wire size like 14awg, 12awg, 10awg.


And without looking it up, at that distance I'm gonna bet you would need 8wg - quite expensive.


But the better way to assess this is to 1) know the answer to the question of "does the cord get warm or do the cord caps at each end get warm/hot?".
2) but even better is to have measured the voltage at the coach with the a/c running, and, measure the current the a/c unit is pulling while running and comparing to nameplate amps - to include the individual current readings for the compressor and fan motor.

[41magnum]

the 50 yds is 12/3 underground

the cord has never gotten warm/hot

its the black RV, fat as a cigar, cord

I was able to run them direct to the 50 amp outdoor outlet yesterday and ran it for 20 mins. Then had to come back to town/home.
Heading out in a few mins to let it run for a couple hrs...…...hopefully.

[MrMark52]

Well -


I'm thinking either a lightening strike or one of the wires on either of the capacitors shorted to the case of the capacitor with a hole in it. The wire that might have failed was very likely one of the leads off of the start capacitor - the high resistance of the PTCR resistor prevented a total melt down and/or tripping of the breaker.


It has happened on my motorhome that the cord caps fail - evidenced at first by the cord cap getting warm, and unplugging the cord gets harder and harder due to the prongs getting oxidized or heat warping. Separate all the cord caps and check for discolored/oxidized prongs on the cord caps.


And just this summer my a/c started tripping the coach's house breaker either at my house or when traveling this summer - whereas from the time we got it last August and morothome-a/c sat in my driveway running, it never threw the breaker. I've bought a new run/fan cap for it as they can go bad (this one is 29 years old) - I just need to get my ladder back so I can get up there and change it out.


All of the above to say - there is not a simple solution to the issues you are having, and there are many factors to be considered when it comes to somewhat erratic breaker tripping. If I understand what you did yesterday by changing the service (and possible power cords used) you've begun to eliminate one of the contributors to the problem without determining why.

[MrMark52]

And thinking a little more -


Does the coach have a generator? If so, you can further help to isolate if the issue is the electrical system feeding the coach, or the a/c unit, if you could run the a/c off of the generator.


Or if you have a generator that you could hook up without all those darned extentsion cords. You would just need to be sure to monitor the cord cap on the cord coming from the coach to make sure it isn't getting warm for the reasons stated previously.

[Petrolero]

Originally Posted by MrMark52

You should see a C to R resistance of around 3-4 times that of the C to S resistance, and infinite resistance from any of those terminals to chassis ground or the steel shell of the compressor.
A word of warning, always, always, always replace the terminal cover on the compressor after insuring all wires are properly connected and separated. I've seen the plugs blow out, and it isn't pretty when it does.

Just making sure I'm doing this right-


I found a fried start cap in the rear unit after taking possession of the '97 Holiday Rambler Endeavor...



Replaced both start caps (front and rear) with the recommended Supco SPP6 - worked great although they're taller than OEM and I had to adjust for that before the capacitor housing cover would go back on-



My questions - I checked ohmage on the compressors - on front or rear I get Common-Start=3.7 or 4; Common-Run=1.0 or 0.9, and Start-Run=4.1 or 4.3... Question being on the ohms for Common-Run vs Common-Start - MrMark did you have your values backwards or did I screw up the ID of the terminals? I was following the labels on the terminal cover- Also the sum of Common-Run and Common-Start is slightly higher than measured - I assume this is ok.



after measuring ohms (I did disconnect the wires first) and replacing the start capacitors I tested the units via the Onan 7000 Marquis - I will say that the Onan runs fairly steady but when a compressor kicks in will drop RPM notedly - and of course voltage drops with it. I note this with a plug-in voltage gauge in the motorhome. Should I worry about this in terms of being hard on these AC units?



Appreciate any observations- I'm probably being way too anal but AC isn't my forte and I'd rather be overly cautious and ask the expert(s).


Thanks!
Petrolero

[41magnum]

new Cap with built in resistor did the trick!