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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8013
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Phil, I have a RV ac ducted that sounds like the compressor

Customer Question

Hello Phil, I have a Coleman RV ac ducted that sounds like the compressor starts when you turn on the breaker to the ac on with the ac off on the thermostat switch on the wall. I can turn the ac on and lower the tempature on wall thermostat and the fan will come on. Any ideas?
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

Hello, so far it sounds like the system might be OK and that you have some confusions about operating it...but I cannot be sure.

Try setting the thermostat on the wall in cooling mode, and up to 90F, and the fan switch on the thermostat if it has one, to FAN auto. Nothing should come on.

Now turn on the breaker, nothing should run if your RV is cooler than 90F inside.

IF the compressor comes on when you turn on the power, air will come out of the vents 20F cooler than the air in the RV at the time.... if it is... we know that it is the compressor you hear running, Check all that to see if that is what is happening or not.

If I miss your response tonight I will pick it up first thing in the morning.

Customer: replied 1 year ago.
Lets start over, I have a Coleman RV air conditioning unit on my RV. It is the duct type. It sounds like the compressor is coming on and running when you turn the breaker on even though the unit is turned off at the wall mounted thermostat. The wall thermostat is set on 90 and the temperature in the RV is 60. I can turn the ac on and lower the temperature on wall thermostat and the fan will come on. Any ideas?
Expert:  Phil replied 1 year ago.

Hello again,

I think I understood you the first time... but I am questioning that the compressor is running, because you said that you *think you hear the compressor running...that is why I prescribed the test and especially the temperature measurement at the cold air outlet.

What you are describing points to either a bad printed circuit card or a bad thermostat... but the are also some contradictory indicators.

So I must ask for these these tests.

Or you can gain access to the units electrical panel and send me a photo of the wiring diagram and I can mark it up with trouble shooting instructions. Its midnight here, I have been up for 18hours, if you like I can stay up another few hours for you, or I can go to bed and pick your response up in the morning.

If you want to do this trouble shooting attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clip icon at the right end of the toolbar at the top of this dialog box,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip icon, look for the '+attach files' link at left of your send button.

I can mark it up with trouble shooting instructions. You will need a multi meter ($30 at a hardware store) and some experience working with appliances, let me know a lot about your skill sets in those regards.

Let me know how you want to do this, we can go from there.

Customer: replied 1 year ago.
I am not at my RV. I will respond tomorrow. Good Night and Thanks
Expert:  Phil replied 1 year ago.

That will work,

Customer: replied 1 year ago.
It is the compressor running while thermostat on the wall is off.
Expert:  Phil replied 1 year ago.

Thanks.

It sounds like the contacts in the large relay that puts power to the compressor that stays running are burnt. and have welded themselves closed. (its called a 'contactor')... its a $40 part. 90% chance that is the problem.

There is a 10% chance that the printed circuit card that sends 24 volt control power to the contactor is bad. ($200+ part).

Please attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clip icon at the right end of the toolbar at the top of this dialog box,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip icon, look for the '+attach files' link at left of your send button.

I can mark it up with trouble shooting instructions. You will need a multi meter ($30 at a hardware store) and some experience working with appliances, let me know a lot about your skill sets in those regards.

We can go from there.

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