Question about Dometic Rooftop RV Air Conditioner

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Brisk Air rooftop A/C starts then bogs down and blows breaker

Mt BriskAir 57915.331 rooftop A/C has less than 50 hours on it. Unit starts and runs with cool air for a few minutes then bogs down and blows breaker. I replaced the RUN Capacitor and it worked for a few hours then the rotary speed switch burned out and it only worked on low speed. I replaced the switch and it it now is back to running a short time and bogging down and blowing the breaker again. What might be causing the unit to slow down and draw excessive current? Where can I get a schematic diagram?

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  • brogow Nov 15, 2008

    There is no power supply board on the BriskAir 57915.331 model.

  • brogow Nov 15, 2008

    There was no short cycle occurance. It went like this:
    1- Plugged into shore power
    2- Turned on AC (High Fan)
    3- Unit ran for approx 15 minutes and then circuit breaker blew.
    4- Replaced Run Capacitor
    5- Unit worked for two hours fine
    6- Used it again a month later and only worked on low speed.
    7- Replaced rotary fan/cool switch
    8- Worked 5-8 minutes and fan slowed down and breaker blew.
    9- Inspection of old rotary switch showed burnt contacts.

  • brogow Nov 15, 2008

    I would think that the refrigerent levels are ok as it worked fine for the first 50 hours of operation. It is a five year old unit that didn't get used much.

  • brogow Nov 15, 2008

    Thanks for the link!

  • brogow Nov 15, 2008

    I'll have to make the measurement. Thanks.

  • brogow Nov 15, 2008

    I just measured the AC current to the compressor. It started out around 7 amps and increased to over 10 amps after about 4 minutes. Does that sound like a dying compressor?

  • brogow Nov 15, 2008

    Since it is "compressing the freon" is it a bearing problem loading it down?

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Yes that is to high of a current draw for that compressor
the compressor is being loaded down by the motor , if it was the bearing you would hear some noise going on from it . I have an air conditioner that quit early in its life and its the same problem , some times parts just don't hold up like they should ( like the old days )

Posted on Nov 16, 2008

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Check the disconnect switch could be faulty or loose connections in unit or disconnect

Posted on Nov 16, 2008

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You have a massive power drain somewhere and its not always easy to locate the drain unless you know how to use an electrical tester and you have to know what the voltage should be, everytime you fix a problem another one occurs, leading you back to the original problem, the process is taking you round in circles, if i were you get a A/C technican to have a look at it, it may be beyond economical repair

Posted on Nov 16, 2008

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Download service manual for from the link---
http://www.rvtechlibrary.com/heatair/aircon.htm

Posted on Nov 15, 2008

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Anything else?

Posted on Nov 15, 2008

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Sounds like the compressor is going,if you have a meter you can do an amp draw on the compressor run wire any high amp draw above 5 would mean your comp.is starting to go,if it amp's out(LRA) comp is about shot-mike

Posted on Nov 15, 2008

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I would look into the possibility of whether the unit is cooling properly as it seems like the pressure is going up too high if it is bogging down. Consider that the refrigerant used in your AC system
increases pressure as it heats up. When the ambient temps go up, so does
the internal pressure. There is a pressure cut-off switch in your system
designed to shut everything down if it gets dangerously high. But that
should not trip the AC circuit breaker. The AC breaker trips when the load
is higher than the rated amps. That would come from too much load on the
compressor. Where would that extra drag come from?

Is it possible that the AC was originally installed with too much
refrigerant? It's easy to test. You should have your dealer hook up a
manifold gauge set to check it. If so, you may also have a bad cut-off
switch.

Posted on Nov 15, 2008

  • Benjamin Patri
    Benjamin Patri Nov 15, 2008

    I'm not saying the refrigerant levels are bad (they could be), but the extra pressure build up from not cooling properly could be causing the motor to bog down (it would be like a kid trying to push a truck) The hotter it is outside the harder the a/c is going to work since the refrigerant will be at a higher pressure. Have you tried running the unit at night when it is cooler. I'd bet that it will run longer since the pressure won't be so high since it will be cooler outside. Give this a try and see what happens, if it runs longer, then you have a cooling problem and/or possibly an excess refrigerant level which will also cause increased pressure. You should definitely look into both of these cases before making any assumptions. True, it may blow colder with more refrigerant, but the motor might not be able to handle what is in it.

  • Benjamin Patri
    Benjamin Patri Nov 15, 2008

    also since it is older, I would make sure that it doesn't have any dust build up and that everything is properly lubricated if needed.

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 would be an electronic short cycle delay. This and digital controls are something all, this means your home units also, air conditioners and heat pumps should have for reliability and efficiency. I have talked a little already about the compressor overload. Many more things can cause a compressor to short cycle in an recreational vehicle then a home air conditioner. Short cycling occurs when someone adjusts the thermostat, a power failure occurs, generator burps or someone trips and pulls the RV power plug within 3-5 minutes of the compressor turning off. The short cycle delay keeps the compressor from trying to restart before pressure in the refrigerant circuit equalizes. When restarted too soon the compressor draws the Locked Rotor Amps ~60 to 75 amps for a 15k BTU air conditioner until the overload opens, a circuit breaker trips or a fuse blows rather then the 12-14 amps it normally draws. In the few seconds before the overload heats up the motor wiring starts to fry, trailer/RV wiring and plugs will be severely stressed and your lights will dim.

Posted on Nov 15, 2008

  • fixyy Nov 15, 2008

    Blower and fan motors should use a "run" capacitor to increase electrical efficiency. The capacitor feeds power to a motor winding at the proper rate and time to boost the motors efficiency and lowers electric consumption by 10 to 20%. The big three use them on compressors so why not the blower motor?



  • fixyy Nov 15, 2008

    the speed of the fan and motod depends upon that RUN capacitor.if the capacitor is not receiving the proper current required.the motor will not spin as per its sdpeed due to this fan will run slow.check out the capacitors connection and the current passing through whole board if its over it will definately blow the breaker or the fuse.any of the option.get the current passing through the unit checked properly at local repair shop to decide a proper problem.

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You might have a short in the power supply board that is causing it to give too much power to the unit after the power board heats up and is used for a few minutes. Since you say it has less than 50 hours on it, it should still be under warranty from the place you bought it. Take it back and let them take a look at it and see what they say the problem is. They should be able to fix it or replace it.

Posted on Nov 15, 2008

  • Jazz Boyce
    Jazz Boyce Nov 15, 2008

    It is still an electrical problem since the inspection of the old rotary switch shows burnt contacts.

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