Forum Discussion

jodeb720's avatar
jodeb720
Explorer
Sep 08, 2020

AC toast?

My wife and I are in the process of doing a makeover on our 5er.
We keep our rv in a storage yard and conveniently, there is power.
It was in the upper 90's so i dutifully checked the voltage - it was 120 spot on! terrific.

I fired up the AC, shut down all the other things in the trailer (converter, etc) and then proceeded to let the AC run.

After about an hour it was comfortable at 83 and we were busy gutting the carpet and preparing the floor.

Then the AC compressor shut off. Hmmm fan stayed on, but no compressor. So I shut it down and let it sit for 10 minutes - thinking it was cycling.

10 Minutes later I turned it on, but the compressor didn't kick in.

again, I let it sit for about 5 minutes, and at that point, I connected my voltmeter and turned it on. The voltage dropped to 95 volts.

Now this is the same power cable I've used when i'm camping so I know it's not a cable issue - and yes, it has a dog bone, but again, I've used this at parks and checked it there as well.

I'm thinking low voltage, hot weather and it may have toasted the compressor.

I did try to start it today running my honda 2000, with the eco off - but no luck. It overloaded the honda. it does have a supco hard start kit I installed 10 years ago -

I need to get the model number (it's a coleman mach - don't know if it's a mach III or not).

I'm thinking it may be toast -

Thoughts?

Thanks in advance!

josh
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Sep 08, 2020
    "We keep our rv in a storage yard and conveniently, there is power."

    What size AMP is that power source......50A, 30A or 20/15A???

    120VAC Voltage below 108V will damage induction motors

    Sounds like compressor motor is toast.
    Time for NEW A/C UNIT
  • pianotuna's avatar
    pianotuna
    Nomad III
    Sep 08, 2020
    You may have found out the hard way that one needs to check voltage under load. I use a hair drier and a kill-a-watt meter to check voltage and polarity under load.
  • jodeb720's avatar
    jodeb720
    Explorer
    Sep 08, 2020
    Old-Biscuit - it's a 20amp circuit.
    Don - yup it's a lesson learned.

    The one question I have is when I bring it home and do connect it to a 20 amp circuit - how can I tell if it's the compressor or if it's one of the start/run capacitors? I'm wondering if one of the "support" devices within the unit failed and that's why it's not able to kick the compressor over.
  • Flute_Man's avatar
    Flute_Man
    Explorer
    Sep 08, 2020
    You really need an amateur in conjunction with your voltmeter to do a better diagnosis. And like said above it could be just a starting capacitor.
    If I were you I would get an experienced electrician or air conditioner guy to check it out And determine exactly what is wrong.
  • bob213's avatar
    bob213
    Explorer
    Sep 08, 2020
    Before you write off the ac at least check the run capacitor. Here's how...
    test capacitor
    If you go to replace it make sure you discharge it before you handle it.
    I use a resistor but you can find instructions on you tube
  • jjrbus's avatar
    jjrbus
    Explorer
    Sep 08, 2020
    This You tube thing is amazing, no more running off to the library to find a technical book written in greek to trouble shoot something. There is a down side, some people can make big screen quality videos but know nothing about the subject or are not really good at speaking to the average person.

    I just had what I am 99% sure is a AC compressor lock up. So I jump on You tube watch a couple videos and go try to test the capacitor. I won't go through the entire story, can't get a micro farad reading on my multimeter, borrow the neighbors, same thing. Stumped.

    None of the videos mention that the average meter a DIY'er has will measure over 20 micro farads. The least expensive meter I could find that will measure over 20 was in the $50 range. HTH
  • jodeb720's avatar
    jodeb720
    Explorer
    Sep 08, 2020
    Once the snow settles down, I'll go check the capacitors (excluding the start capactors).

    I have a friend who is an HAVC guy - but in order to test it, i'll have to pull the unit from the trailer and take it up to his house (it's an hour away) to see what's going on with it.

    Can you check the wiring on the compressor to determine if it's toast? for example, on some of the motors, you can check the resistance of the stator and if the resistance is more than 'x' then you know it's done.

    Of course, if it's done, then I can look for a more efficient unit that uses less current. I know there's some "high efficiency" units that are being made now - so that may be something to investigate.
  • jjrbus's avatar
    jjrbus
    Explorer
    Sep 08, 2020
    There are you tube videos on checking compressors, easy to do. I have found no way to check for a seized compressor which is what I believe is my issue. I asked on an HVAC forum and it seems to be a process of elimination, if all the electrical checks out then a sized compressor is assumed. A rather expensive assumption!
  • dougrainer's avatar
    dougrainer
    Nomad
    Sep 08, 2020
    You made a COMMON error in your first part of your post. You stated you checked the Voltage and spot ON at 120. I could run a 500 foot extension cord and with no load I would have 120 volts. VOLTS is NOT AMPS available. Storage yards rarely have anything above 15 amps and that is usually nominal. Now, you stated your Genset would not start the compressor, so yes, old AC and LOW voltage may have hurt the compressor. IF the AC is over 10 years old and you are doing a makeover, I would just replace the Upper AC unit. Doug
  • Seon's avatar
    Seon
    Explorer II
    Sep 08, 2020
    For about $25 I'd buy and install a hard start capacitor that very easy to install. Mine was tripping the coach circuit breaker until I installed one and now it runs great.

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