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Old 10-07-2013, 08:09 PM   #1
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Rooftop AC not working

My rooftop AC is getting the 120VAC, but does not come on. Nothing, no click, no fan, no compressor sounds, nothing!
The RV was sitting for a couple of years in the desert.
Suggestions on how to get this puppy running again?
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Old 10-07-2013, 08:37 PM   #2
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Brand or model, age, RV make....whatever info you can supply helps.

Perhaps someone with the same rig has had the same problem.
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Old 10-07-2013, 10:57 PM   #3
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Originally Posted by Arch Hoagland View Post
Brand or model, age, RV make....whatever info you can supply helps.

Perhaps someone with the same rig has had the same problem.
1987 Sportscoach 30' = Motorhome
1987 Briskair By Domestic (DuoTherm) = Rooftop air conditioner
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Old 10-08-2013, 12:53 AM   #4
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What is your ambient temp? They will not operate below about 35 Deg F if you are asking it for heat.
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Old 10-08-2013, 01:41 AM   #5
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What is your ambient temp? They will not operate below about 35 Deg F if you are asking it for heat.
Haha I live in California. Today was around 87 F.
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Old 10-08-2013, 02:40 AM   #6
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How is your 12 Volt side of things??? Is your thermostat getting voltage. They won't work if your thermostat isn't sending them a signal.
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Old 10-08-2013, 05:30 AM   #7
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You have a Dometic system. They used both analog control systems (same as your house) and prioritary digital systems. This is easily determined by the thermostat. A digital display, 4 or 5 push buttons and a slide switch for on/off. They also say Comfort Control Center.

Once we know what you have, we can help better. Any RV A/C system needs 12+ VDC for it to operate, as well as fridge and furnace. So I would check the batteries and that the converter/charger is charging them when connected to shore power. Also a good time to check all 12v fuses.

You said it had 120v, do you know that by checking right at the A/C unit itself? If not, a good time to check all 120v breakers too.
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Old 10-08-2013, 10:47 AM   #8
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You have a Dometic system. They used both analog control systems (same as your house) and prioritary digital systems. This is easily determined by the thermostat. A digital display, 4 or 5 push buttons and a slide switch for on/off. They also say Comfort Control Center.

Once we know what you have, we can help better. Any RV A/C system needs 12+ VDC for it to operate, as well as fridge and furnace. So I would check the batteries and that the converter/charger is charging them when connected to shore power. Also a good time to check all 12v fuses.

You said it had 120v, do you know that by checking right at the A/C unit itself? If not, a good time to check all 120v breakers too.
Since the RV is quite old, nothing is digital. There is a separate thermostat for the Furnace shown in the picture below. However, there is not a visible thermostat for the rooftop AC.

The AC is getting 120 VAC to the breaker and to the unit itself. Same with the frige.
The furnace is on the DC system and the dash air/heater is off the engine battery like in any reg vehicle.
From the pictures of the Air Conditioner unit it appears that something else should be plugged in there that is not. Maybe?
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Old 10-08-2013, 11:31 AM   #9
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Try to look up your model on this website and see if they still have the manual. Support - Dometic

Typical modern unit uses a 12v powered thermostat to control 120 v A/C, many problems happen when no 12v power is present. Same goes for refrigerator, furnace, and water heater. They all require 12 v for operation.

The photo of the dash HVAC control implies you think it has something to do with this issue? The dash control operates A/C compressor on engine, just as in an auto or truck, it has no control on 120v rooftop A/C.
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Old 10-08-2013, 12:09 PM   #10
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There are two things that run and make noise in an AC.....the Fan and the Compressor. They are separate units, but both require 120 VAC to run, in addition to a signal from the Thermostat telling the control board to turn on which mode, "cooling" (fan and compressor) or "fan" only. In your case, you say neither works. If you are confident you have 120 VAC to the control box, then you have a defective Thermostat circuit or something Kaput in the control box. Rook
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Old 10-08-2013, 12:15 PM   #11
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The knob on the right in your photo, the one that's labeled "cooler" is your thermostat. Rook
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Old 10-08-2013, 12:21 PM   #12
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You can put selector switch on hi cool all the way on cool then go to your t-stat take front cover off and move lever from 50-90 degrees and watch mercury bulb to make sure it is making contact being a light 12 volt spark between contacts.

If you have 12 volt to t-stat trace to control board check voltage out of control board to capacitor make sure capacitor is not swollen or busted , check voltage out of contacts to fans and compressor .

Did it just stop working or has it been having problems not coming on or not cooling.

Hope this helps,

James
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Old 10-08-2013, 12:58 PM   #13
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In one of the photos, there is a green wire hanging down. That likely is a lead that went to the "freeze" sensor that is mounted in the evaporator coils. When the coils freeze, this sensor cuts off the AC and lets the ice melt. The sensor is normally open and closes when the coils freeze......so if I am correct about this, make sure the two wires in this lead are not shorted to each other. That can keep the AC from coming on. Rook
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Old 10-08-2013, 07:15 PM   #14
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You can put selector switch on hi cool all the way on cool then go to your t-stat take front cover off and move lever from 50-90 degrees and watch mercury bulb to make sure it is making contact being a light 12 volt spark between contacts.

If you have 12 volt to t-stat trace to control board check voltage out of control board to capacitor make sure capacitor is not swollen or busted , check voltage out of contacts to fans and compressor .

Did it just stop working or has it been having problems not coming on or not cooling.

Hope this helps,

James
there's not a mercury bulb just a metal coil.
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