RV Furnace And AC Run At The Same Time: Ultimate Answer

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If your RV furnace and AC run at the same time, this is something you should investigate. Not only are you not getting the desired temperature, but you could also be wasting propane or shore power.

The most common causes of your RV furnace and AC running at the same time are an incorrect thermostat setting or a faulty thermostat. This post will review how you can:

  • Set to correct thermostat setting
  • Check your vents
  • Check for a faulty thermostat

This article will walk you through the proper set-up of your thermostat as well as the easy check of your RV furnace and RV AC system.

Table of Contents

Thermostat

An RV thermostat is a basic device that controls the temperature by either turning on the air conditioner fan or the furnace fan. It will allow that fan to run until the desired set temp on the thermostat setting meets the room temperature. So, if your wall thermostat is set to cool at 72 degrees, the air conditioning will run the fan until the room temperature is at or just below 72 degrees. No surprise there.

Thermostat Setting

Where the issue may arise is in the thermostat setting. As we reviewed, a thermostat is a basic device. Its function is only as good as what you set it to. And in many cases, when set incorrectly, it can give undesired temperatures. Let’s look at the correct settings and the common cause of the RV furnace and AC running at the same time.

Furnace

Once you set your wall thermostat to HEAT, the thermostat wire signals the furnace blower motor to turn on and for the propane in the gas furnace to start producing heat. When this happens, the blower fan starts immediately, providing air that is not yet warm or hot air.

Since the furnace heat exchanger takes about 15 seconds to produce heat, you will initially receive cold air from your vents. This sometimes feels like the air conditioner fan is running, but it is just the furnace blower fan starting before there is any heat in the furnace (this is normal).

Set Fan Motor to Auto

Another setting to check is your thermostat fan position switch. Your RV thermostat should have a fan setting of either “ON” or “AUTO.” The blower fan will always be running when in the “ON” position. Even when set to HEAT, once the room temperature meets the setting temperature, the RV furnace will turn off, but the fan will keep running.

Set the fan to “Auto” position.

Since the furnace is off (without producing heat), the air coming from the blower fan will feel like cool air. This is not cold air from an air conditioner, but rather just the room temperature air circulating. This may sometimes feel like your air conditioner is running at the same time as your furnace, but this is not the case, and this is the normal function.

To avoid this cool air from the furnace blower, I suggest you set your thermostat to the “AUTO” setting. This setting will only turn on the furnace blower fan when heat is needed to reach the desired temperature. Once the desired room temperature is met, both the RV furnace and furnace blower will turn off. This will avoid that cool air feeling between the furnace cycling on and off and running when hot air is available.

Air Conditioner

Now, let’s take a look at your AC system and see if there is an issue with it.

Your AC unit is similar to the furnace system in that they are both controlled by the wall thermostat. You either set the thermostat to “COLD” or “HEAT,” depending on what you want temperature you want. That is where the similarities end.

Your air conditioning unit and AC fan both run on-shore power, whereas your furnace will use propane to produce heat and DC (battery) power to run the blower fan.

Vents

Another difference between your RV AC and RV furnace is the venting system. Your RV air conditioning is a central air system that uses its own vents, separate from the furnace vents.

We all remember hot air rises and cold air sinks from grade school. Well, this principle is used in your RV heating and cooling system. Your RV AC provides cold air only from vents located at the ceiling. That is because once the air leaves the vent, it will naturally sink, giving you more consistency in air temperature.

AC only comes out of ceiling vents.

The opposite is true for your RV furnace. The furnace only uses the vents located on your RV’s floor. That way, once the hot air leaves the vent, it will rise throughout the camper, giving you more consistency in air temperature.

So, if you suspect your RV furnace and AC are running simultaneously, check your vents. If you are only getting air from the floor vents or only the ceiling vents, then the units are not running at the same time. If you are getting air from both the floor and ceiling vents simultaneously, move on to the next section.

Faulty Thermostat

Above, you reviewed the typical RV furnace and RV air conditioner operation. The biggest clue to determining if you have an issue is when both cold and hot air come out of different vents simultaneously. If you have this situation, the most common cause is a faulty thermostat or faulty wiring.

Since the thermostat controls your RV furnace and RV AC, it can get faulty and send the same signal to have both units run. Here is a quick step-by-step guide to see if you have an issue with the thermostat:

  • Step 1: Check your thermostat battery. Low voltage in a battery will give odd signals and could cause problems.
  • Step 2: Check the wires to the thermostat. There are usually 3 to 5 low voltage wires to the thermostat. Check to make sure no wires are touching each other.
  • Step 3: Reset your thermostat. This could be a glitch in your thermostat, and a quick reset may work.

If you have gone through the three steps and both units are still running, the issue is likely a faulty thermostat that will need to be replaced. For more info on thermostats and replacement, visit my post on thermostat troubleshooting.

Final Thoughts

If you find your RV furnace and AC running simultaneously, it’s crucial to investigate the issue promptly. The most common culprits for this problem are incorrect thermostat settings or a faulty thermostat. Understanding the proper thermostat settings and how your RV’s heating and cooling systems work is essential to resolving the issue. Remember that the thermostat controls when and how these systems operate, so a faulty thermostat or wiring can lead to both units running simultaneously. By following the steps outlined in this article to check and correct thermostat issues, you can ensure efficient and comfortable temperature control in your RV, ultimately enhancing your camping experience.