Air conditioner thermostat

fixerupper

Well-known Member
Our air conditioner is a commercial wall unit like what you see in a motel. It can put out heat or air conditioning. When it is running the fan is on full time, the compressor cycles on and off to control the temp. The thermostat has stuck on so it cools full time which is better than sticking in the off position but 61 degrees in the house is a little too cool. It is a 20,000'ish BTU unit that runs on 230v. Can I wire a remote thermostat into the power plug so the whole unit turns on and off controlled by this thermostat? I know the fan and compressor will shut down with no fan delay. Just wondering if my idea will work.
 
There's no reason it wouldn't work, as that's exactly how a central AC operates/cycles. You will need a HD enough line-v0oltage thermostat for the job, or a thermostat and contactor.

Short-cycle/start delay protection would be good unless the system already has it.
 
I would not recommend it.

First, you won't find a thermostat that will handle the amp load. You would need to add a contactor, that is going to get expensive and involved to do it safely.

Second, you will somehow need to disable the ac to use the heat mode. Possibly, depending on how it is wired, if you turn it to heat, both the heat and ac will be on.

It would be safer and easier to fix it right. The thermostats are somewhat universal, so should not be too hard to find one.
 
Let's say you go out to start your truck or tractor. When you turn that key, is the full power of the battery going through the key switch and then to the starter? No. The key activates a solenoid or relay, which then directs full battery power to the starter. Same thing here. Your thermostat will have very tiny wires in it which cannot handle much current. Yet the relay it is connected to "can" handle that much power. So yes, it can be done, so long as it's done correctly.

You might consider buying a book that talks in depth about wiring up a home A/C, or you could have a professional install a thermostat for you. Best place to install a single thermostat is near the middle of the living quarters, as that will help the thermostat provide the most equalized comfort for all rooms. But to do that (and remember, I'm old-school - maybe there's a newer way now), one would need to run thermostat wire from the thermostat to the relay, which will be at/near the A/C unit. I used to see old-school telephone wire used for this purpose sometimes, but I know that's nearly unheard of these days.
 
Base board heating units use a line voltage thermostat I have installed more then one of them but they are for heating. But yes they make thermostats that handle line voltage be it 110 or 220
 
Many of these units are wired with wall thermostats, so there must be a way to bypass the internal thermostat. That said, you should still try to first find the fault with your unit, since the fault may not be in the thermostat itself.
 
Hello fixerupper,

Take a look a the bulb end of the thermostat. It should be clamped to the evaporator, may be the clips
rusted out, or broke off? You may get lucky,

Guido.
 
(quoted from post at 21:44:23 07/29/17) Base board heating units use a line voltage thermostat I have installed more then one of them but they are for heating. But yes they make thermostats that handle line voltage be it 110 or 220
Yes, after re-reading the OP, I suppose 20,000 BTU's is well within the range of an inline thermostat. When I think about other than window A/C's, my mind goes to those large, power hogging units I grew up with in SE Texas. But our little window A/C is 5,000 BTU and only pulls 4A @ 110v, so yes, 20,000 BTU should be easy.
 
Thanks for the replies. I assume the unit's
thermostat is fairly generic and easy to
replacement. After I got to thinking about this
it would be more work and expense to rig up
a remote thermostat than it will be to
merely replace the unit's thermostat. This
unit is mounted fairly high in the wall and
is above the entertainment center so
removal isn't going to be a walk in the
park.
 
Complete thermostat access should be right behind the front cover, typically should not have to remove unit from housing.
 
I just got done working on some "PTAC" units like you describe. Find a copy of a manual. The use of a remote thermostat is usually a built in option. You will probably just need to find the terminals to connect to, and slide a switch to "Remote" position. You should not have to get a heavy duty Line thermostat.
 

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