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 two-stage AC.
I have a 2007 Winnebago Journey that has a two-stage basement air conditioner. It has always worked well until now. The second stage is not kicking on. Was told at the service center that 95 percent of the time it is that the thermostat is bad and not calling for the second stage. After spending $181 on a new thermostat, the second stage of the two-stage AC is still not activating. What else can I check? The first stage is cold but not enough for the summer heat. Thank you in advance. —David
What you have is a Coleman unit that Winnebago called “TrueAir” and it is actually two compressors in one compartment. These are exactly like the units on the roof, just more efficient in the lower compartment and ducted to the ceiling.
The first unit was introduced in a Vectra and was located on the driver’s side in the middle of the coach. It was a great concept, but was discontinued as it eliminated a storage bay, which was a selling issue.
The number one compressor is the main or default compressor of the two-stage AC and runs all the time. The number two compressor turns on when the temperature raises 4-5 degrees above the thermostat setting and number one cannot keep up. Thermostats have been an issue with almost all types of AC units. However, it’s not a 95 percent issue as your dealer indicated. Just swapping out the thermostat is not the answer, as you have experienced.
How to diagnose the thermostat
The thermostat can be diagnosed by using a multimeter and verifying 12-volt power going out – which should have been done before. What needs to be done is to verify 120-volt power is getting to the second compressor. Winnebago has wiring diagrams available online for your unit. My tech source indicated the orange wire going to the second compressor is the 120-volt power line and should be checked.
To test, set the t/stat at a lower setting than ambient temperature inside the rig, let’s say 75 degrees with an ambient temp of 90 degrees. When the first compressor starts up, you know the temperature sensor is working and you should have 12-volt power on the yellow wire coming off the t/stat which is for the main compressor. After one minute, the second compressor should start up which would mean the orange wire off the t/stat would have 12-volts. For a troubleshooting path, download the pdf file here.
Also, I would suggest contacting Winnebago to get the correct wiring diagram for your unit, then verifying 12-volt power from the thermostat to the second compressor, 120-volt to the second compressor, and then you will find the problem.
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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.