Clicking in A/C when furnace kicks in

arniez · 11-21-2016, 07:59 AM

I have a Keystone Passport travel trailer with a Dometic air conditioner. There is a series of clicking sounds, sometimes just a few, sometimes up to 20, before the furnace kicks in. Then a couple of clicks while the furnace is running, and then another series of clicks when the furnace is shutting down. I brought the trailer to my dealer to have them check it out and they couldn't find anything wrong. As usual, the dealer said they couldn't duplicate the clicking, which is crazy because it happens all the time. Is anyone else experiencing this? Thanks.

**JRTJH** · 11-21-2016, 08:07 AM

The Dometic HVAC system "interconnects" the A/C, furnace and thermostat. With the thermostat in AUTO, the thermostat will call for either A/C (cooling) or furnace (heat) independently. With the thermostat fan switch set to HI or LO, both the A/C fan and the furnace fan will be called to operate with the thermostat set in the HEAT position. So, the clicking you hear is probably the A/C relay panel which is located in the overhead unit.

You might "play" with your thermostat settings and try AUTO which should not call for the overhead fan, HI or LO which should cause the overhead fan to come on at the speed setting selected when the furnace is operating.

Dometic's thermostat manual gives the explanation of this "feature" as being incorporated in the function to help distribute warm air by supplementing the furnace fan with the A/C fan to help provide more even air distribution. No argument that it does "move more air" but whether it's helpful or just added noise ???? That depends on the individual owner's take on how the system works.

Tbos · 11-21-2016, 10:18 AM

My passport does this if I have the thermostat temperature differential set to 1 degree. If I use auto heat with 2 degree differential it works with no AC clicking. The thermostat book can tell you how to change the differential setting. It was frustrating enough to me that I'm willing to put up with the larger differential.

arniez · 11-21-2016, 10:20 AM

Thanks for the response. I do have the fan in auto all the time. Are you thinking I should put it in hi or low to see if that has an affect? Also, this never happens when the A/C goes on.

arniez · 11-21-2016, 10:22 AM

Thanks Tom, I will try that. I too have the differential set to 1.

Tbos · 11-21-2016, 04:03 PM

With 2 degrees differential it's easier to feel the difference before it comes on but the annoying click is gone.

scott24 · 11-30-2016, 05:32 PM

Are you possibly hearing the spark ignition and it keeps sparking due to poor flame and it keeps trying to lite even tho its running?

Tbos · 12-01-2016, 02:27 PM

I know in my case the clicking is in the AC and not the furnace.

arniez · 12-02-2016, 04:17 PM

My clicking is also definitely coming from the A/C. Unfortunately, I will have to wait until the spring to see if the differential adjustment will stop the clicking as we've winterized the trailer and it's stored for the winter.

Tbos · 12-03-2016, 09:18 AM

Quote:

Originally Posted by arniez

My clicking is also definitely coming from the A/C. Unfortunately, I will have to wait until the spring to see if the differential adjustment will stop the clicking as we've winterized the trailer and it's stored for the winter.

Let us know if that solves it.

Ken / Claudia · 12-03-2016, 10:48 AM

Besides hearing the spark ignition, I have thought some clicking sounds was from the sheet metal or other parts clicking or popping as hot or cold air is being pushed thru the system. Anyone else have that thought.

arniez · 01-21-2017, 10:27 AM

Tom, I changed the furnace differential to 2 as you recommended and my brief initial test was successful. There was no clicking. I will do a more extensive test when we do our first trip this spring. Thanks for your help, and all others who responded.

Arnie Z.

Tbos · 01-21-2017, 08:22 PM

Quote:

Originally Posted by arniez

Tom, I changed the furnace differential to 2 as you recommended and my brief initial test was successful. There was no clicking. I will do a more extensive test when we do our first trip this spring. Thanks for your help, and all others who responded.

Arnie Z.

Glad it looks like it worked. I would prefer to use true 1 degree setting but it seems the systems just plain get confused so I'll stick to 2?

2016 Passport GT 2810BHS, 2014 Silverado 1500 LT in Deep Forest Green

arniez · 06-25-2017, 04:23 PM

This is a follow up to my clicking in A/C problem. As was recommended by Tbos, I changed the furnace differential to 2 degrees instead of 1. In my brief test last winter, the change solved the problem. This past week I was able to do a more extensive test while camping in Yellowstone. I am very pleased to report that the clicking did not recur. The furnace was on a lot as the temperature dipped to 34 degrees during the nights. Thanks again Tom.

Tbos · 06-25-2017, 04:53 PM

Quote:

Originally Posted by arniez

This is a follow up to my clicking in A/C problem. As was recommended by Tbos, I changed the furnace differential to 2 degrees instead of 1. In my brief test last winter, the change solved the problem. This past week I was able to do a more extensive test while camping in Yellowstone. I am very pleased to report that the clicking did not recur. The furnace was on a lot as the temperature dipped to 34 degrees during the nights. Thanks again Tom.

Glad it worked. I would prefer a 1 degree difference but our systems can't seem to make up their minds when set that way.

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McClure · 01-13-2019, 05:28 PM

My clicking sounds like it is coming from the thermostat itself. Heater works fine but that noise is annoying. It just started doing it this winter with my first tank of propane.

Tbos · 01-14-2019, 04:25 PM

Quote:

Originally Posted by McClure

My clicking sounds like it is coming from the thermostat itself. Heater works fine but that noise is annoying. It just started doing it this winter with my first tank of propane.

If your thermostat is set on one degree difference I’m not sure what might be causing the issue. I’d try changing the difference Ist. Others have recently had to change their thermostat.

jmatte70 · 02-07-2020, 10:55 AM

Is the differential changed on the thermostat itself? My New Cougar 5th wheel did the same thing. It's winterized now, but I'll also change the differential setting to 2. Thanks for the info. I hope this works for me as well.

Tbos · 02-08-2020, 08:02 PM

Quote:

Originally Posted by jmatte70

Is the differential changed on the thermostat itself? My New Cougar 5th wheel did the same thing. It's winterized now, but I'll also change the differential setting to 2. Thanks for the info. I hope this works for me as well.

That’s what did it for our last rig. The new rig doesn’t have this type of thermostat.

208boondocker · 10-11-2020, 09:57 AM

so we recently switched the a/c unit to 1 degree differential and discovered this annoying clicking before and after the furnace kicks on. pinpointed to relay box in a/c unit. we have the same dometic unit everyone seems to be referencing here, it is nice to know this is a common issue. has anyone found a way around the ac relay to stick to a 1 degree differential setting? we have a 2017 passport 2890rl, it appears this issue is well known. we live in idaho so we use the furnace frequently throughout the year. is there was a way to shut off the a/c relay in winter time and bypass it altogether?? then enable it for summer, that would be awesome.... maybe not possible, but if anyone knows??

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