Air conditioner turns on with furnance

[jerryneal]

I turned on the furnace for the first time this season and the air conditioner turned on as well. Through the Summer, the air conditioner ran only on its setting. I had some roof repairs this Spring and the roof unit was pulled and replaced. Is it possible to miswire the air conditioner to cause this problem?

[Ronbo]

Is it a heat pump?

[orbiker]

Try setting the fan setting to auto.

[Chief 62]

Pop the front of the thermostate off and spray some electrical contact cleaner on the micro switch that controls the setting and work it back and forth a couple of times. It may just be dirty contacts.

[Kirk W]

We don't really have much to go on as it would help to know the kind of air conditioner (make & model), and the make/model of the thermostat. Also what furnace you have. I would not start spraying chemicals into things until I knew more about what you have and if you do that, make sure you have the power to it turned off.

 

... I had some roof repairs this Spring and the roof unit was pulled and replaced. Is it possible to miswire the air conditioner to cause this problem?

Yes, that is possible, but it is difficult to know just what may have happened. The thermostat control circuitry passes through the air conditioner and then to the furnace when the same one controls both units. Most RV furnaces have a thermostat line that goes to a switch or set of contacts which is then either open or closed, with the closed position causing the furnace to turn on. In many thermostats there is just a set of contacts that open or close based upon the selected temperature, and the circuit inside of the air conditioner then sends the signal from the thermostat either to the air conditioner to make it turn on when temperature rises, or to the furnace causing it to turn on when temperature falls. For both to turn on at the same time would be a control function since a/c starts with a rising temperature and the furnace should start with a falling temperature.

 

There are thermostats today that have more of the control function in them, while the more simple ones are only a set of temperature controlled contacts. I suspect that yours is one of the more intelligent thermostats with a solid state control board and multiple outputs. It could have just two wires out if the most simple of thermostats, or it may use a telephone cable type of output or some other multi-wire cable, depending upon make and model.

[weaverworks]

I think you need to investigate the above question..."is it a heat pump/air conditioner." On my Mach 8, if you have the thermostat set more than 5 degrees above room temperature, the furnace will come on with the heat pump/AC. For just the heat pump, you must set thermostat within that 5 degree setting. For just furnace you set on "electric heat."

 

Not sure what you have but worth checking.

[Ray,IN]

Kirk is right, not enough information to even make an EWAG.

Provide make/model of RV, details of new roof units, details of new thermostat, etc. if you want anyone to offer a cogent reply.

To answer your question; yes it is possible to mis-wire things.

[57becky]

If you have a Dometic CCCII thermostat, like what was already said, you must have the fan switch set to AUTO. If you have it set to LO, MED, or HIGH, the A/C fan will run, but the A/C compressor does not run.

[jerryneal]

If you have a Dometic CCCII thermostat, like what was already said, you must have the fan switch set to AUTO. If you have it set to LO, MED, or HIGH, the A/C fan will run, but the A/C compressor does not run.

Well didn't I just have a Homer Simpson moment. I've had the 5th wheel for over 2 years and guess the thermostat was place on AUTO for the first time. Set for HIGH and that fixed the problem. One of those tips you don't find in the manual. Many thanks.