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Ask Dave: Air conditioner unit works, then doesn’t. What gives?

Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the RV Handbook and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses a malfunctioning air conditioner.

Dear Dave,
We have a 2004 Jayco 5th wheel trailer with an air conditioner that cools and then waits a long time before it starts up again, leaving us cool then hot. We have asked our local RV dealer to help, but they say there is nothing they can do. Do you have any suggestions, or is this just the nature of the beast? —Gayle B.

Gayle,
To provide more specific troubleshooting information regarding your roof air conditioner, we need the make and model of your air conditioner. Since it’s a 2004 model, it should be either a Dometic or Coleman, and I’m assuming ducted since it’s a 5th wheel? The next thing is to record the temperature. Your roof air conditioner can only cool ambient inside temperatures down about 16 degrees, so any technician trying to help troubleshoot will need to know the temperature that is coming out of the vents and the temperature that is at either the thermostat or the temperature sensor called a thermistor. You can use an infrared thermometer.

How the thermostat works

The thermostat is powered by 12-volt house batteries and should call for the air conditioner to start within 4-5 degrees of what you are setting the thermostat at. If it gets warmer than that, I would suggest first testing the condition of your house batteries. Typically the house batteries will drain down to approximately 50 percent and the converter kicks on and charges them back up. If your batteries are sulfated, they will not hold a charge as intended and can drop rapidly. If your temperature rises to the point the air conditioner should turn on, but the batteries are weak, it will have to wait until the converter kicks on to charge them. You can verify this by plugging in an external battery charger and see if that helps.

The problem could be the thermostat

Another issue could be the thermostat itself, as these have been the frustration of many RV owners. We have a local campground in our area and have changed out about 10 of these just this summer! Make sure you get the correct model for your unit as some have zones and others do both the air conditioner and the furnace. If you have a zoned unit, such as the Dometic model, there will be a thermistor in the bedroom that senses the temperature. These are very inexpensive and easy to change.

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Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club, a one-stop go-to online resource for RV enthusiasts. 

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Tony Grigg
1 month ago

My thermostat is located in a spot where it is covered by the bathroom door when the door is left open, and we have to leave it open due to a cat needing access to his litter box. The door prevents air from passing over the thermostat and controlling the A/C. So just be sure you have nothing shielding air flow from the thermostat.

Chip
1 month ago

Does the thermostat have an “AUTO” setting for the fan? If so, (and all is working correctly), if it is set to “AUTO,” the system will run until the set point is reached. Then the fan and compressor will shut down until the ‘stat turns things back on.

Mine is a 2007 Class A, two temp zones, Duo-Therm 5-button thermostat, with “AUTO,” “LOW,” and “HIGH” fan-speed settings toggled by the “FAN” button.

Just something else to check.

Thomas D
1 month ago

There are NO batteries in my thermostat.weren’t any in my last 2rv’s neither.
You ghink the CHEAP manufacturers are going to spend mone for a digital with clock when they can get one without. Batteries cost money. Maybe at wholesale 50 cents for two.😀

Lee Ensminger
1 month ago
Reply to  Thomas D

Thomas, he was referring to the 12V house batteries…

Bob
1 month ago

If the air from one of the ducts is blowing toward the thermostat area, it will cause the same problem. The air cools the wall and the thermostat housing. It has to wait until the wall itself warms up again.
Another thing is the thermostat itself. If it’s an analog thermostat, the temperature differential, may be 4-6 degrees. That is something you can feel.
My TT came with a Coleman analog and it was terrible. I changed to a digital thermostat and the differential is now about 1 degree.

Bob p
1 month ago

I learned something about converters, I didn’t know that the converter didn’t run constantly keeping the battery and all 12V accessories working.

Kyle
1 month ago
Reply to  Bob p

Mine does. I’ve always used Progressive Dynamics units and when the rig is plugged in it and the batteries are charged the converter holds the voltage at 13.2V. If the rig is unplugged the fully charged battery reads 12.7V after given a bit of time to bleed off the static voltage.

Dennis Wieske
1 month ago
Reply to  Kyle

That’s correct Kyle, Progressive Dynamics converters are always operating when AC power is applied to the rig This voltage is anywhere from 13.2 to 14.6 VDC depending on the charger’s mode of operation. In addition, it will be charging or maintaining the battery and supplying.com power for the 12 volt accessories.

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