A/C Thermostat Question

[richard5933]

We have two Custom Coach a/c units. They have line voltage thermostats that turn the compressors on & off via large relays.

The a/c units cool great, but there is a problem. They cool too great, so much so that the compressor only runs a short time before reaching the temperature set point, sometimes only a minute or two. This means that even though the temperature is right the compressor isn't running enough to remove humidity from the air.

What I'm looking for is a way to add something to the thermostat circuit which will guarantee a minimum run time, say 5 minutes, even if it means cooling the temperature more than needed.

Any ideas on how to accomplish this?

[chessie4905]

Why not just run one?

[richard5933]

Why not just run one?

We do this when we camp on a 30-amp site, but it doesn't really reach front to back. Our center hallway is really tight and we have to stand a fan in the hallway to get the air to flow through, which essentially blocks the hallway.

[sledhead]

can you slow down the air movement fan speed ? if so that will help with the cycle time

dave

[buswarrior]

If power is available, if you aren't being metered, if you don't care and just want it dry...:

Run a heater concurrently with the AC.

Or get a dehumidifier?

Dehumidifier is good kit, especially when the coach is not being used.

Built in someplace is really trick.

Most funky coaches have been damp inside.

Defend against the stink!

Happy coaching!
Buswarrior

[Jim Blackwood]

Open the windows?

[chessie4905]

If the two ac units are next to each other, interconnect the outputs so one running can reach all the coach.

[richard5933]

First picture is the front unit. Output is to the right, intake is the grill on the left. The thermostat is just below the intake. There is no other ducting.

Second picture is the rear unit. Grill showing is the output. Thermostat is just above it. Intake is underneath the unit, just behind/above where the TV is located.

The third picture is the narrow hallway between the front and rear of the bus.

Somehow I thought that some type of delay relay would be the simplest solution by just extending the compressor run time.

[chessie4905]

If the thermostat sensor is in the front of the evaporator like household units, you could put a soda straw over the tube to make the thermostat less sensitive. You could look for an ac thermostat that you could wire in that has a sensitivity adjustment.

[richard5933]

The thermostat on these units are line-voltage (120v). The thermostat sends 120v to the compressor relay which controls the compressor. Really simple system - when the thermostat determines that cooling is needed, it completes the circuit to the relay. The relay turns on the compressor. When room temp is met and room is cool, thermostat opens the circuit to relay and compressor stops. The only temperature sensor is inside the thermostat itself, nothing inside the evaporator controls anything.

What I was hoping to find is some type of time delay relay which can be wired to the thermostat circuit going to the main compressor relay. My hope is that this delay relay would be able to keep the relay circuit energized for a set period of time, even after the temperature setting is reached.

There are many types of delay relays out there, but I am getting lost trying to find the type I need.

[RichardEntrekin]

You need a 120V Delay on Break adjustable relay. Many different brands. Put that term into google and you will find what you are looking for.

As you wire it in, keep in mind two things. One, it must be installed so that the inside and outside (evaporator and condenser) fans run any time the compressor is running. Second, the whole unit will obviously run for the delay time after the tstat turns it off, meaning it will get even cooler.

[richard5933]

You need a 120V Delay on Break adjustable relay. Many different brands. Put that term into google and you will find what you are looking for.

As you wire it in, keep in mind two things. One, it must be installed so that the inside and outside (evaporator and condenser) fans run any time the compressor is running. Second, the whole unit will obviously run for the delay time after the tstat turns it off, meaning it will get even cooler.

Thanks Richard. Having the proper search term  is a great first step.

The evaporator fan is always running if the a/c is turned on. The condenser fan runs anytime the compressor is triggered by the thermostat (the compressor relay also turns on the condenser fan). So, we should be good to go on the fan front.

Yes - I'm aware that we'll drop below the thermostat set point a bit having the compressor run longer than needed solely for cooling. I'll report back once I have a chance to scour the interwebs for a relay.

[buswarrior]

You'll still have the problem. It will run a little longer, get cooler, and then not come back on for a longer time.

The lengthened run time, less frequently, is likely not going to be sufficient to get the air dried out.

Happy coaching!
Buswarrior

[chessie4905]

Maybe the actual problem is output air restriction, causing short cycling of the compressor.

[sledhead]

we carry a 16" fan similar to this and use it inside and outside to make the air move . works great
we got ours at a hardware store in Florida for $ 30

https://www.grandandtoy.com/ProductDetails?productCode=LLR33982&gclid=CjwKCAjw-vjqBRA6EiwAe8TCk-j056Y0k-9eJCQF4ICNcsCcEOY_M-5xMRS-V0doKLNjQSLQ-j0zCRoCfXMQAvD_BwE

dave