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Old 11-10-2019, 09:43 PM   #1
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Thermostat for roof top AC

Hey all. Own a 2020 Bambi 22FB. It has the ‘manual’ roof top AC by Dometic. By manual I mean no thermostat. You turn it on through temperature and fan knobs on it. Anyway to retrofit a thermostat to control it? If so, big job or fairly easy? Any info welcome. Thanks.
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Old 11-10-2019, 11:08 PM   #2
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I'm sure it can be done, but why not give it time to see how it works? A thermostat on a wall only has the advantage of numbers in a temperature range. I like our wall thermostat, but find I fiddle with it a bit to get comfortable and don't often use a specific # setting. If we didn't have it, and the dial on the a/c worked well at maintaining a good temperature range, I doubt I'd spend the time and money to change things.
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Old 11-10-2019, 11:16 PM   #3
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Changing a ‘manually controlled’ air conditioner to use a really thermostat would require adding at least two high current AC relays or solid state switches to the air conditioner innards, then finding an appropriate digital thermostat that could then control those relays and either run on internal batteries or be powered off 12 volts DC.

That said, it’s one of those projects sitting on the ‘back burner’ at the Department of Overkill Engineering around here. Once I get the rest of the myriad projects like another shore power port and a transfer switch working, the backup and side view cameras installed, and a few other hoodies like the battery monitor installed, I’ll ‘get right to it’.
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Old 11-11-2019, 06:19 AM   #4
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Quote:
Originally Posted by rowiebowie View Post
I'm sure it can be done, but why not give it time to see how it works? A thermostat on a wall only has the advantage of numbers in a temperature range. I like our wall thermostat, but find I fiddle with it a bit to get comfortable and don't often use a specific # setting. If we didn't have it, and the dial on the a/c worked well at maintaining a good temperature range, I doubt I'd spend the time and money to change things.

The big advantage for us would be the AC stopping when the set point is reached. Right now, it runs until we turn it off. Not ideal at night. You have to get up to go and turn it off and then perhaps on again when it gets warm.
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Old 11-11-2019, 11:11 AM   #5
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The big advantage for us would be the AC stopping when the set point is reached. Right now, it runs until we turn it off. Not ideal at night. You have to get up to go and turn it off and then perhaps on again when it gets warm.

That's not good, I can understand why you want something better. But it seems your unit may not be working as intended. I would contact Dometic about it.

Also, you might ask them of they offer a unit with digital thermostat controls on the inside cover as an upgrade. I did not find such an offering during a quick Dometic search on-line, but the reason I mention this is Coleman offers such an upgrade.
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Old 11-11-2019, 11:51 AM   #6
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I have the same basic unit with the fan control and thermostat.
You should not have to get up and physically shut the unit off. If you set the thermostat at, say, “5” the unit should cool until about 74 deg (at least on mine) and then the compressor kicks out. The fan keeps running. Once the thermostat senses about 77 deg, the compressor kicks back on and so on and so forth.
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Old 11-11-2019, 02:48 PM   #7
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I had the electronic Comfort Control Center electronic thermostat. Until it stopped working and I couldn't revive it in the middle of nowhere.

I upgraded to a manual control unit.
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Old 11-11-2019, 04:36 PM   #8
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Originally Posted by n2916s View Post
I have the same basic unit with the fan control and thermostat.
You should not have to get up and physically shut the unit off. If you set the thermostat at, say, “5” the unit should cool until about 74 deg (at least on mine) and then the compressor kicks out. The fan keeps running. Once the thermostat senses about 77 deg, the compressor kicks back on and so on and so forth.

Sorry, you are correct. I wasn’t clear in my OP. Mine does that too. What I’d like to be able to stop is the fan itself given how noisy it is. In a nutshell, I’d like to be able to have the fan on auto so that it runs only when the compressor in on.
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Old 11-11-2019, 06:39 PM   #9
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Originally Posted by steilkurve View Post
Sorry, you are correct. I wasn’t clear in my OP. Mine does that too. What I’d like to be able to stop is the fan itself given how noisy it is. In a nutshell, I’d like to be able to have the fan on auto so that it runs only when the compressor in on.
On my older Dometic unit fan on or auto was an option on the rotary control switch.

If yours doesn't work that way I'd bet it could be modified to run the fan with the compressor by moving a wire.


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Old 11-12-2019, 09:44 AM   #10
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Originally Posted by steilkurve View Post
Sorry, you are correct. I wasn’t clear in my OP. Mine does that too. What I’d like to be able to stop is the fan itself given how noisy it is. In a nutshell, I’d like to be able to have the fan on auto so that it runs only when the compressor in on.

Ah. Be careful what you ask for.

We have the ability to "cycle" the fan on and off with the compressor (auto mode), or let the fan run continuously (fan mode). We find the noise change of fan running, then the abrupt silence of it turning off to be a huge annoyance that prevents us from getting a good nights sleep.

But maybe that's just us since we normally sleep with a "white noise" sound machine. But we don't need the machine when sleeping under the ac with continuous fan blowing.
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Old 11-12-2019, 11:18 AM   #11
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Dometic has crappy thermostats regardless of wall mounted or on the unit. All the ones I have had short cycle and won't stay on when temps get into the 70's. You can use a generic digital thermostat but you will also need some relays. The contacts in the thermostat can handle a few amps to cycle the relay. I think you only need one relay. The you put 12V on one pole of the thermostat and that goes to the input of the relay. The output of the relay has your compressor. If you also want to control the fan you need a second relay. I would leave the fan running 100% controlled by the knob and then use the thermostat to control the temperature. You can also control your furnace with the same thermostat.



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Old 11-12-2019, 08:45 PM   #12
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Originally Posted by perryg114 View Post
Dometic has crappy thermostats regardless of wall mounted or on the unit. All the ones I have had short cycle and won't stay on when temps get into the 70's. You can use a generic digital thermostat but you will also need some relays. The contacts in the thermostat can handle a few amps to cycle the relay. I think you only need one relay. The you put 12V on one pole of the thermostat and that goes to the input of the relay. The output of the relay has your compressor. If you also want to control the fan you need a second relay. I would leave the fan running 100% controlled by the knob and then use the thermostat to control the temperature. You can also control your furnace with the same thermostat. Perry

Thanks for the reply. It’s helpful. So, to get this straight, I’d need a relay that interrupts power to the rooftop AC unit based on whether or not the set point has been reached. That means I would not need to fish a wire that goes from the unit to the thermostat but simply ‘intercept’ the 120 wire that goes to the AC from the trailer’s electrical or am I getting this wrong?
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Old 11-14-2019, 11:46 AM   #13
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You would connect the relay to the compressor just like the manual thermostat does now. It would be the 12V in series with the thermostat relay would go to the input of the compressor relay.



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Old 11-14-2019, 12:22 PM   #14
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Check to see if they sell the inside part of the ac that has controls for a thermostat.
Ie the part that currently has your dials.

At least when I was researching a coleman, you could get either inside controller for the same unit.
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