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Old 06-30-2020, 09:53 AM   #1
Skins44
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AC Unit Question (fan/cool)

Hello all. I have a 27' Outback. AC unit runs well, however occasionally to be on the safe side i power it off to use the microwave or wife needs the blow dryer. I have 30 amp and the hair dryer will trip the breaker almost every time.

My question, when i put the thermostat back to "cool" the AC doesn't always kick back on. I have to put it on "fan" for about 15-20 seconds, then flip it to cool.

Is this normal?
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Old 06-30-2020, 10:12 AM   #2
flybouy
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First question what thermostats do you have? We have 30 Amp and a 15K A/C unit. When the DW uses the microwave she moves the thermostat from "cool" to "fan". This keeps the A/C fan running and stops the compressor. Once the microwave is finished she moves it back to cool. No delay in the compressor kicking in.
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Old 06-30-2020, 10:23 AM   #3
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its a Coleman-Mach. Original one with the camper. i realized i could just bump it over to fan while we run the microwave for hair dryer. We will do that for now on.
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Old 06-30-2020, 11:00 AM   #4
sourdough
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Originally Posted by Skins44 View Post
Hello all. I have a 27' Outback. AC unit runs well, however occasionally to be on the safe side i power it off to use the microwave or wife needs the blow dryer. I have 30 amp and the hair dryer will trip the breaker almost every time.

My question, when i put the thermostat back to "cool" the AC doesn't always kick back on. I have to put it on "fan" for about 15-20 seconds, then flip it to cool.

Is this normal?

Just as an fyi, we have a 50A trailer and when I turn off the main AC for whatever it takes several seconds for the AC to come on then the compressor so you don't have anything defective IMO.
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Old 06-30-2020, 11:24 AM   #5
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any recommendations on an aftermarket thermostat? Maybe something digital?
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Old 06-30-2020, 11:42 AM   #6
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Originally Posted by sourdough View Post
Just as an fyi, we have a 50A trailer and when I turn off the main AC for whatever it takes several seconds for the AC to come on then the compressor so you don't have anything defective IMO.
Our 13.5 Dometic does the same (30amp trailer). It a built-in delay. I believe this is so you don’t get fan and compressor start surges at the same time. First the fan up to speed and then the compressor.
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Old 06-30-2020, 07:39 PM   #7
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On any air conditioner with a compressor, there will be a time delay after turning it off and then back on, so the pressure in the Freon lines has dropped before starting the compressor. If this didn’t happen, you would be starting the compressor against very high pressure in the lines and would probably burn up the compressor motor. There should be as much as 90 seconds or more of a delay before the compressor starts.
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Old 07-01-2020, 02:28 AM   #8
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Originally Posted by bobbecky View Post
On any air conditioner with a compressor, there will be a time delay after turning it off and then back on, so the pressure in the Freon lines has dropped before starting the compressor. If this didn’t happen, you would be starting the compressor against very high pressure in the lines and would probably burn up the compressor motor. There should be as much as 90 seconds or more of a delay before the compressor starts.
Ah! That makes better sense than my thoughts. If I remember correctly now, it’s something called “head pressure” that has to come down before a restart. The bigger the compressor, the longer the delay.
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Old 07-01-2020, 03:34 AM   #9
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Originally Posted by bobbecky View Post
On any air conditioner with a compressor, there will be a time delay after turning it off and then back on, so the pressure in the Freon lines has dropped before starting the compressor. If this didn’t happen, you would be starting the compressor against very high pressure in the lines and would probably burn up the compressor motor. There should be as much as 90 seconds or more of a delay before the compressor starts.
^^^^^
Exactly! Well stated
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Old 07-01-2020, 05:59 AM   #10
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The way a Dometic A/C is "supposed to work" (not the way it "might work) is to start the compressor, then momentarily later, start the fan. The reason for operating that way is to start the heaviest draw with the most available current, then start the lighter draw with the available power remaining after the heavy draw motor is operating. That sequence provides the maximum amperage to start the compressor, then when it's running, uses the remaining amperage (of the 20 amps that can pass through the circuit breaker) to start the fan motor.

When the thermostat setting is reached, the shutdown process is to shut down the compressor, fan remains running for about 30-60 seconds to push all the cold air out of the coils, eliminating the problem of increased condensation from humidity remaining in the air box. That humidity would condense on the coils and either drip into the airbox or sit on the coils and eventually start to mold.
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Old 07-01-2020, 08:11 AM   #11
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Originally Posted by flybouy View Post
First question what thermostats do you have? We have 30 Amp and a 15K A/C unit. When the DW uses the microwave she moves the thermostat from "cool" to "fan". This keeps the A/C fan running and stops the compressor. Once the microwave is finished she moves it back to cool. No delay in the compressor kicking in.

I disconnected the microwave's electrical wires and connected them to an all weather Marinco outlet on the rear of my trailer and plug into a 15 or 20A camp ground outlet on the pedestal using a heavy duty cord. I find cooking bacon and being cool to be one of life's greatest pleasures.
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