A/C Thermostat Question

[Jim Blackwood]

Don't think he wants to hear that Lin. He has an idea he wants to try, maybe after that hasn't quite met expectations he'll reconsider.

Jim

[richard5933]

Lin - I agree that the thermostat placement is not ideal in this install (see photo posted earlier). In addition to the delay relay I'm going to be adding a shield of some type below the thermostat to prevent the air from the a/c outlet from hitting the thermostat. If necessary I can move it to a new location later on, but in a room this small there really are not a lot of options. The side walls are out since they are all windows and/or draperies, and the opposite wall is out since it is in the direct flow of air from the a/c output. In some ways, the current position may be the least-bad option.

[Lin]

Of course you are limited by the configuration that you may have inherited from the PO.  In rooftop RV units or home window units the sensor is generally right at the air return.  The return air is a good measure of the ambient room temperature.  You may not be able to move it to an ideal location.  One possible problem with shielding the sensor as you mention or protecting it as I mentioned earlier is that although it will extend the run time before the compressor cycles off, it may also delay the compressor from cycling on. You may be able to compensate for that by playing with the on/off gap in your thermostat, since I think you mentioned that it was adjustable.

[richard5933]

The on/off gap is not adjustable. I was hoping it was, but it's preset.

The air return on this unit is on the horizontal surface under the a/c unit. Hard to see in the photo, but it's above and behind the TV. While that would be the ideal place to mount the thermostat, it would then be nearly impossible to see or adjust without doing gymnastics.

I'm going to try the relay and shielding and see where to go from there.

Thanks for all your comments.

[chessie4905]

Set this in front of the air intake. Only draws 200 watts.

https://www.amazon.com/Lasko-102-Personal-Ceramic-Heater/dp/B00538G5PI/ref=sr_1_26?gclid=EAIaIQobChMI5f_Bvqmp5AIVC6_ICh2qjwl7EAAYASAAEgKHvfD_BwE&hvadid=295586692239&hvdev=t&hvlocphy=9006537&hvnetw=g&hvpos=1t1&hvqmt=b&hvrand=8801101653989429424&hvtargid=kwd-374833943687&hydadcr=29443_10730058&keywords=150+watt+space+heater&qid=1567124450&s=gateway&sr=8-26

[Jim Blackwood]

I'd suggest buying a 20 to 40ft length of wire for your thermostat (it sounds like lamp cord could work, maybe even an extension cord) and then try putting it in various locations in the coach until you find one that works. Then figure out how to mount it there permanently. Try corners that are out of the direct airflow, high locations, the opposite end, and spots where you think dead air and return air might be. A little trial and error goes a long way.

Jim

[buswarrior]

Moving the thermostat isn't going to fix anything.

The temperature in the coach/zones was not the complaint.

Short cycling of the compressor, as every AC does when the load is small, and the resulting dampness, was where this started.

But keep typing, the Google ad dollars are rolling in for Gary!

Happy coaching!
Buswarrior

[Jim Blackwood]

BW I rarely disagree with you but this time I must. If it were accurate then the thermostat could be put in the center of the discharge vent and we know that doesn't work because nobody does that.

If you have an accurate enough thermometer (and humidity tester) you could go around the bus and find temperature gradients. It will be warmer by the windows for instance. We all know this is true, just the same as it is colder by the windows in winter. So for instance, if you stuck the thermostat on the window the AC would stay on longer because it would take longer to get the window cool. Now granted once you have it cool it should cycle a bit faster but as that is where most of the heat comes in, it won't cycle as fast as it does now. What's it cost to try it? A pair of skinny wires and a little time. That is way easier than splicing in relays. And if it doesn't work you've lost nothing.

Jim

[richard5933]

The room is only about 7' x 9' with windows & drapes down two of the four walls. The opposite wall from the a/c unit is in the direct flow of the output. Not many options.

BW has the right thought here - the unit is oversized once the room is cooled off, especially when it is not too hot outside and/or humidity is high. Best solution would be a multi stage compressor, but that isn't going to happen.

I figure it will take less than an hour to install the relay. That option does the least harm to the cabinetry, and I will try it before moving to other approaches. This concept works well in our S & B system, so I hope that it will on the bus as well.

[buswarrior]

The result of running the compressor longer will be cooler temperatures inside, initially, and then the same short cycling at that lower temperature.

The inside temp will now be uncomfortable for the inhabitants, and it will still be damp.

We're chasing the humidity, not the temperature.

Traditional AC has always been challenged to do this under low load conditions. Adding heat is the only solution.

A dehumidifier does this by having all the refrigeration equipment blowing the heat of the condenser back into the same spaces as the evaporator. A dehumidifier by itself will warm a space to a small degree.

Some of the mini-splits offer a dehumidifier setting, which is really handy for a busnut.

Or, in our case here, a $20 cube heater running in the space to put an artificial load on the AC, so it runs more, and dries the air along the way.

BUT... there's NOtHING WRONG with experimenting and fooling around to see what various equipment might be able to squeeze out, performance wise. If Richard can fool his particular unit into doing just enough to make him happy, then the whole exercise has been worth it.

And if it doesn't, he still had fun messing around, and it kept him out of the bar?

Happy coaching!
Buswarrior

[Jim Blackwood]

Sure, worth trying. What's the worst that could happen?

Jim

[richard5933]

Having fun experimenting, for sure.

Even if the delay relay doesn't fix the humidity problem it will keep the compressor from cycling on for such a short period of time and will serve as somewhat of an on/off gap (which on my thermostat setup is not adjustable.) I know the temp will drop a bit more than the thermostat set point with the extended run time, and I also know what the compressor will stay off a bit longer between runs since it now has to climb back up further. That little feature in itself will be welcome, as the frequent on/off of the compressor isn't conducive to sleeping since the relay in the a/c compressor unit downstairs makes a loud noise every time it engages. (It's been checked - it's normal - it's a downside of using a commercial refrigeration unit in an application like this.) The noise is not my primary concern, but maybe the delay relay will help with that even if not with the humidity.

[chessie4905]

Or you could crack a window open. Adjust the crack till the desired result is achieved. Or install a speed control on blower motor.

[richard5933]

Or you could crack a window open. Adjust the crack till the desired result is achieved. Or install a speed control on blower motor.

Wouldn't that just let more humidity inside?

[peterbylt]

Just a thought here.

The Mini Spit in my bus is controlled by a remote.

The temperature can be controlled either by an internal sensor in the return of the Minisplit unit, or a setting on the remote called "Follow me" that is controlled by a temperature sensor in the remote control.

Usually we leave it on the internal sensor, but on occasion use the sensor in the remote.

Something like this could work for you, a quick Amazon search came up with this.

https://www.amazon.com/Nashone-Temperature-Controller-Thermostat-thermostat/dp/B071NG8MZK?ref_=fsclp_pl_dp_9

Peter