Question Air conditioning problem

[cobraracing93]

I have a rv that came with dometic air conditioners. And replaced one with a Coleman. I’m having issues with the dometic acting up with the thermostat. I have heard that you can’t run 2 different air units on that one thermostat. How can it be fixed to operate right ???

 

[TR25]

(worked hvac for a while, but never rv stuff).

a thermostat just send out a heat/cool call to a board in an appliance. as long as the coleman is hooked up correctly on the board, I don't see where it would be a problem as the tstat will send the current to the pin and the board will do what's needed.
Assuming thy're hooked up correctly, I'd check the voltage at the appliances to see if they are getting the correct amount during the call for cooling. If the other one worked, don't see why the coleman wouldn't work too.

 

[cobraracing93]

I read somewhere that they both communicate differently. And they need a thermostat that matches the air unit ??

 

[TR25]

I read somewhere that they both communicate differently. And they need a thermostat that matches the air unit ??

In the settings that I've worked, each furnace/ac got their own thermostat. How a tstat works is it reads the temp where it's at, then send out the heat/cool calls to the unit to do something. So to me it doesn't make sense for a tstat to control 2 units if it only has the ability to read temp in one spot. but may be that's an option in an rv as it may be big enough to 'need' 2 ac units, but overall it's still a small container. If that is the case, then one tstat controls BOTH.
So then, how was it hooked up before, one or 2 tstats? If one controlled both, then there's gotta be a way for that to happen.

Auto/rv is different than residential, down to the coloring of the wires, but hvac is hvac. To see if this is something you should consider tackling, I'd find a wiring diagram for your unit and/or for an RV like yours with multiple AC units. Look and see how that is wired. See if you can make sense of that.

For example, if there's only one tstat that controls both, the wiring may be done in series or parallel, so the first unit may also control the second unit. If it's a dif mfgr that may be the problem, but I doubt it as current is current. But who knows anymore w/all the computers out there.

See if you can make sense of the wiring diagram. Check to see it's wired correctly also. Check to make sure it's getting the right voltage....and most simply, is the coleman a good unit to begin with? Most coleman items other than their 50 year old lanterns aren't very good. So just hooking up a not good unit in the same area as a good one, there will naturally be a difference.

Some things to think about so you can figure out where to go from here.

 

[TR25]

I read somewhere that they both communicate differently. And they need a thermostat that matches the air unit ??

Separating out this response.
A tstat just senses temp then sends current to the AC/furnace, which then the unit will turn on the heat/ac and run until the tstat senses where it is at is the temp setting, then stop current to that...and the ac/furnace will then shut down.

Basically that's all there is to it. This is why you have to answer the question how many tstats are there in your RV. 2, then one for each. 1, then it could be a communication problem as it's more complex.

In a house, one furnace/ac can control different floors/rooms differently. This is done by controlling the flow of the conditioned air going through the ducting, directing it to where it's needed. These areas are called "zones".

In order to know the temp in each zone, there has to be a tstat there. Multiple tstats are connected to a furnace/ac and that's done on the board inside the air handler (furnace/ac box). A zone's tstat senses it needs to cool down, it sends that signal to the furnace/ac box, which then turns on and closes the other ducts in the ducting system but keeps the one open for the zone that tstat controls. That's how it's done.

Doubt if it's done that way in an RV, even the bigger ones, but don't know for sure. That's why you need to look at the wiring diagram. If you can figure that out, you should also be able to figure out the 'system' there, what and how it works.

Who replaced the ac unit? Have you contacted them?
Maybe call a mobil tech or a shop you trust and ask them?
If this is a prob and more than you care to bite off, may be worth it just to pay someone else to fix it or at least check it and say that's the way these work (coleman vs better ones).