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Old 06-05-2012, 09:00 PM   #15
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Rook have you check the amps and volts and compared them to the rear A/C?

ken
Ken.....No, I have not. I'm too old and fat to get up there. I would expect them to measure slightly different since they are not identical. The front AC has more capacity and likely a larger compressor.

Seems to me that there has to be some sort of "switch" that turns the power off to the compressor..........because the demand for "on" from the thermostat is continuously present because the compressor starts again immediately just as soon as the compressor delay ends. Rook
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Old 06-06-2012, 04:44 AM   #16
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Hey turn the breaker off to the a/c that is not staying on for a few hours, During that time pull the cover and check airflow through the evaporator with flashlight.

Then find the high pressure switch on discharge line two wires then jump it out or make contact together.


Then turn breaker back on if the compressor stays on more than a few minutes it has a high head due to evaporator dirty, Or a high pressure switch going out, If you can amp out the red wire on compressor the amp load should be on the compressor.


Do not continue to run a/c unit with high pressure switch jumped out. Wire it back together.
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Old 06-06-2012, 06:41 AM   #17
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If it is kicking off after 10 seconds it has nothing to do with dirty coils or blocked vents. It sounds like the start capacitor has gone bad. It is trying to turn on and will not so the thermal protection circuit comes on and shuts it down and it cools down and within two minutes tries to start again. Since you say you are unable to get on the roof then it is time to pay a professional.
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Old 06-06-2012, 06:55 AM   #18
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The reason it is clicking off is the internal Klix-on switch or Thermister in the compressor motor. It is a heat sensitive device tha protects the compressor. If the start or run capicator is bad, it will cause the motor to trip off die to the heat protection device.

The unit will not have a high pressure or a low pressure switch.

With te inside cover off, you should be able to access the power feed and can check voltage and amps at the total unit. The label inside the unit should list the amps for the compressor and fan running as well as just the compressor. Inside you can read the amsp for the fan plus compressor.

The only way to get to the capaicators is going up top and removing the cover. Adding a "hard start" kit or a 5-2-1 kit may solve the problem if the capicator is week. In any case, if you replace the capicator, I'd add the hard-start kit. Makes starting a lot easier on the compressor.

I have spent the past 42 years working on industrial refrigeration and I really hate working on A/C units. So I generally hire a tech and watch over his shoulder to work on the home A/C units. If it gets to be more than a capicator, control board or a fan motor on these roof top units, I just repalce the unit. It is not worth the cost to break into the refrierant system.

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Old 06-06-2012, 08:03 AM   #19
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Hey Rook , the hard start kit will not hurt to be put on , it is pretty cheap.

Generally when your start/run capacitor goes out the compressor won't do anything but humm and overheat.

You can test your capacitor with a ammeter for capacitance . I don't know if you have 2 capacitors or 1 , If you have 1 , part of the capacitance is for your evaporator fan motor to help it start up.


Is your rooftop outside fan running? While the compressor is not.
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Old 06-06-2012, 01:05 PM   #20
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Here is why I'm doubtful that it's the "starting capacitor". The starting capacitor's job is to add the initial boost of power to get the compressor running......this boost only last for a second or two. Once the compressor is "running", the capacitor's job is done. Right? This compressor starts just fine and runs normally for about 10-15 seconds.......that's a fair amount of time and well beyond the time of starting capacitor's influence....right? Then it cuts off. And.....if it was a heat problem causing the overload switch to cut out.....then how could it possibly get that hot in 10-15 seconds from a cold start?! However, the overload switch could be defective and cutting out at a very low heat level........that's what I'm now thinking is the culprit. I'm now working on a way to bypass that. Rook
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Old 06-06-2012, 01:19 PM   #21
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Yea,If the start relay drops out. If not, you are running on the start AND run windings. Hire someone to look at it. Quit guessing. Take the top off and check for any hot spots(burnt looking). Maybe you will get lucky.

Also, see if the capacitor has a bulge in it.

And I think you are going to find that the overload is internal of the compressor
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Old 06-06-2012, 01:31 PM   #22
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Yeah.......I think you may be correct about the overload switch........It's likely inaccessible, inside the compressor housing.....UGH! And, if it's defective, that requires a NEW compressor.....or a whole new system. Rook
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Old 06-06-2012, 02:01 PM   #23
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It might be tripping out on your load sheding system if you have one. Just cut out 3 good 15,000 Penguins compressors where a guy decided to go under a low bridge.
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Old 06-06-2012, 02:11 PM   #24
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"Load sheding system"?.........well, since I don't know what that is, I guess I don't have one. Rook

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It might be tripping out on your load sheding system if you have one. Just cut out 3 good 15,000 Penguins compressors where a guy decided to go under a low bridge.
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Old 06-06-2012, 02:19 PM   #25
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Rook your logic is at fault to real world. If that start capacitor is bad and that compressor does not kick up to speed right away then it is going to continue to either not spin or spin slowly and the windings of the motor in the compressor motor are going to get hot real fast. Most likely it is trying to start and that is why it takes 10 seconds for the windings to heat up and kick the thermister and shut it off. Also after it cools down then it will try again in two minutes.
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Old 06-06-2012, 02:30 PM   #26
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Sorry Mike.....but you must have missed the many times that I have said that the compressor starts NORMAL and runs NORMAL for 10-15 seconds.. Not starts slow, not starts humming, not buzzing, not groaning, not anything but perfectly NORMAL speed, sounds perfectly Normal! Cools perfectly Normal.......but initially cuts off after 10-15 seconds. But runs for longer periods for up to 1 minute 15 seconds in later cycles. Rook
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Old 06-06-2012, 04:02 PM   #27
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Thought I would add these comments that I sent to Dick Berry, a valued and frequent contributor to the National Motorhome section of this Forum.....He knows the answer to just about any question on National MH's....

Dick.......I unplugged the freeze sensor.....and that didn't fix the problem. I used a flashlight to look up into the evaporator area and it's definitely dirty but not plugged. If I can find someone to get up there and remove the cowling to brush and vacuum the evaporator fins, I will do that. I do not expect that to fix the problem, just improve the cooling efficiency. I turned off the AC breaker to the front AC and discovered that the back AC does not work with no power on the front AC........is that normal? Must be some signal from the front control box that is required for the back AC to work. With the panel cover off the control box, I can hear a relay "click" when the front compressor stops and I can hear the "click" again when it comes back on. A switch somewhere is turning on and off. I am now wondering if the overload switch might be defective......it is normally closed and that energizes the relay (K6) which the AC power goes through to turn on the Compressor. If it opens from heat in the compressor, it causes the relay (K6) to open and that stops the compressor. If I can get inside the control box, I can use a volt meter to see what is happening on the terminals of K6. If the overload switch, mounted on or in the compressor, is the culprit, then I can temporarily short across it via the control box and see if the compressor continues to run normally. Of course K6 could be bad, but I doubt it. Does removing the plastic frame around the AC air intake gain better access? Rook
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Old 06-06-2012, 06:51 PM   #28
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I had a simular problem and it turned out to be the starting capacitor - $22.00.
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