AC short cycling....

[oscar]

Strange goings on with the AC's..... yes, both.

Have the thermostat set to "AU", as I like the little bits of peace and quiet in between cycles.

Bedroom AC fan comes on, then the compressor. Runs for about a minute, then compressor shuts off and the fan about 10 seconds later. Wasn't doing that when it was hot, hot, just overnight.

The only thing I can think of in the bedroom is that the thermostat is directly in the path of one of the side vents on the unit..... This to me looks like bad planning, but am not an AC specialist.

This morning the salon AC did the same thing, but then came back on a minute later and ran for a while......

Scratching head.....

 

[Rickhansen]

Hi Oscar,
I think you are on the right track with the bedroom. My thermostat is on the curved wall near the bathroom door. Unless I set both of the vents that face the rear of the coach to blow toward the off-door side bedroom wall, the AC will short cycle badly.

Cycle time will be much less when the heat load is down, so that might explain what's happening on your main unit. Not sure what type of thermostat you have, but there sometimes is a setting for Cycles per Hour, (or differential). I have Hunter programmable thermostats in our rig. I can set the CPH and have to change the setting based on weather we are heating or cooling and change this seasonally. On the Hunter T-Stat, this is done by pressing the setpoint up and down arrows at the same time for a couple seconds. The display will come up with a value between 1 to 3 degrees(which is the differential). You can adjust the value with the up and down arrows again.

The lower differential can cause short cycling, but the longer differential can cause more noticeable temperature swings. I tend to get more concerned when the "off" part of the cycle is short, rather than a short "on" time. My Hunter thermostats have a feature in their firmware that will prevent the compressor from re-starting less than 2 or 3 minutes after they have been shut off. That prevents a "hard start" where the freon has not equalized and the motor windings cooled down.

Hope this helps, you might need to play around with your systems to get them the way you like them to operate.

Also, there is a brand new Heating and Cooling Users Guide that was recently posted in the Manuals/Guides section of the website. It is a "homegrown" document that offers more of a layman's guide than the OEM technical literature, as well as practical advice from owners.

 

[westxsrt10]

Ours does that.....I put a sandwich bag over the thermostat and that stablized it.

 

[rgwilliams69]

Our 4100 was going that last month when we were in Florida. Turned off the front AC and reset the main AC, then front AC back on and everything seemed to work fine. I agree with your observation that we were in a spot where the front kept turning off the main. Interrupting the cycle seemed to work okay. Not sure how that will work for the long run, but as you also mentioned this was under low load - when it gets nice and hot I am not sure the front AC will get the main thermostat down enough to turn it off. We like to keep it pretty cool inside.

 

[oscar]

Hi Oscar,
I think you are on the right track with the bedroom. My thermostat is on the curved wall near the bathroom door. Unless I set both of the vents that face the rear of the coach to blow toward the off-door side bedroom wall, the AC will short cycle badly.

Yup, same location here..... But I didn't think about the adjustable registers in the vents, wife likes to keep the UV out of the bedroom, so it's a bit dark in there. I shut them both down on the side facing the thermostat, we'll see what that does.

Never knew about the temperature differential setting. Found the manual on lime for my Dometic

3313192 thermostat and read about it. Interesting. Not messing with it right now, as the salon system seems to be behaving.
​

Thanks for all the good stuff.

 

[Rickhansen]

Your welcome Oscar,
I also looked at the Dometic manual. Your T-Stat has a two minute delay on a call for cooling, too. That should be adequate to protect your compressor. Your differential is also adjustable from 1 to 3 degrees.

rgwilliams69,
If you are seeing the main thermostat being affected when the bedroom AC is on, you might look at staggering your setpoints. This is also addressed in the Heating and Cooling Users Guide I referenced in my earlier post.

 

[oscar]

Actually, the "misbehaving" bedroom AC was the only one of the two on last night. (Wife likes it cool, daughter in salon likes it warm).

The salon AC has behaved perfectly all day now...... (The bedroom AC is off.)

 

[rgwilliams69]

I'll give that a try next time we are using the ACs Rick, thanks - still getting used to the rig. As for right now, it's 27 degrees with a wind chill of 20, so not much AC brewing. We only had it on for a bit down in FL anyway to take the humidity out of the air, but it will be on near constant this summer I'd say.