O/T: Window AC temp control

Thought maybe there were some fellow tinkerers who'd worked on one of these little window units before.

Little GE 12,000 btu that belonged to some meth heads who abandoned the house they had rented. I've took this apart and tried to get the filthy human and garbage smell out of it. Tag shows made in 2016. Real good shape except for the stench.

Digital soft key control pad. No problems with functions on the control pad.

What's happening is poor response from the temperature control and I'm trying to determine if it's the little temperature sensing thermistor or something else.

I turn on the unit and let it run.. temp set point is as low as it will go~ 61°. It's 70 in the shop... compressor doesn't start. I finally hold it against my warm body... got it up to 85º and the thing finally starts.
Put sensor in air stream from evaporator and watch temp drop right on down to 37º.. but system isn't satisfied and compressor keeps running. I finally put it in a cup of snow and it drops down to 35º... and in about a minute it finally shuts off.

The temp display on the control pad is really responsive to
the temperature changes with the thermistor.

That makes it hard for me to determine if the thermistor would be bad.

I don't know how quickly the electronic controls for the unit should respond.

I found a replacement board out of a working unit for sale on ebay for $50. Finding repair parts for these import window units is difficult.

What is your thoughts on the possibility that the sensor is faulty and causing this problem.... or would it be the logic in the controls circuit board not seeing the input from that sensor?

If the thermistor is giving a reading at all, does that mean it's good.. or could it give the right reading, but the logic to turn the compressor on or off isn't getting through?

Does it do this in warm weather or only when it is relatively cool outside. Window units seem to work best in warmer weather. Mine doesn't want to work very well in the spring or fall, otherwise it does a great job. It is a big one, about 30,000 BTU.

JH

Some GE (and other brand) window units have a secondary temp sensor. You only mentioned "the sensor", so I thought I would mention this. Might not be your problem. I would google the model number and find the wiring schematic.

You don't really have any good methods of testing either the sensor or the control board. I guess you could search for the specs of the sensor and try to test it, but that may be a real PITA.

And your time is also worth money. With a lifetime of troubleshooting of various devices I would suggest changing the least expensive part first. If that does not do it, then move up to the more expensive ones. That's probably the cheapest way to fix this AC unit.

And if the actual cooling system is working OK, it is probably worth the effort and expense to fix it.

Another thought: if you can rig it to just run all the time, you can purchase an outside thermostat that switches the AC power to the unit. I have an electric heater here in my office that has only an on/off switch. I added a thermostat in a electric box that is in the power cord for the whole unit. I can adjust the temperature easily with that.



I placed it on the heater for the photo. Normally it sits on a nearby shelf. I butchered a heavy duty extension cord for the wiring.

These thermostats are made in two or three varieties: for cooling, for heating, and with contacts for both. You would need either one for cooling of one for both functions. Search for a 115V thermostat. In the past I did this on a window unit that was installed above the ceiling of a room where access to the controls would be very difficult. It worked well. This would definitely be easier to find and likely less expensive than the actual parts for that unit.

Yeah, I see what you are all saying.

I have another small window unit that had a mechanical thermostat that went bad. I couldn't determine the exact replacement part number. The copper contacts inside it were burnt...
I've determined that the reason these get burnt out is from the compressor attempting to restart before high side pressure has equalized out after shut off by satisfied thermostat setting.

I removed the offending bulb type thermostat and instead of messing around looking for the O.E. part number and buying it, I did the most expensive thing instead of part searching.

I put in a little 24 v. relay in place of the t'stat... then bought one of those round Honeywell wall mounted heating/cooling t'stats, and paired it with a 24vac doorbell transformer... and rigged all that up.

Put the Honeywell on the bedroom wall, plugged the transformer in, wired it to the Honeywell and to the relay inside the AC unit.

It works good.. looks like shit with all the wires running everywhere.... but it works.

If I don't end up fixing this the right way, I could always do the same thing with this unit.

JoeE. said:

I put in a little 24 v. relay in place of the t'stat... then bought one of those round Honeywell wall mounted heating/cooling t'stats, and paired it with a 24vac doorbell transformer... and rigged all that up.

Put the Honeywell on the bedroom wall, plugged the transformer in, wired it to the Honeywell and to the relay inside the AC unit.

It works good.. looks like shit with all the wires running everywhere.... but it works.

If I don't end up fixing this the right way, I could always do the same thing with this unit.

Click to expand...

Or simpler. 3rd party T-stat that needs no relay, and mount it on or "closer to" the unit being controlled. If that position gives the T-Stat a distorted world-view? Just crank it a few degrees off the target number to some other number where it hits your comfort zone OK. Or that of a cheap thermometer.

I have two of the 5,500 BTU by GE, and don't expect to get the third full season out of them. BFD. They were only $120 each, wudda been cheaper-yet, ELSE higher BTU had I but grabbed end-of-season closeouts and put them by for the next summer.

As will, next year. Not worth a lot of mess-with, any of these.