Furnace Relay Clicking

2nd House · 11-25-2018, 10:19 PM

Hello All
42' 2014 360 PDeck with two A/C's
When I run the furnace, I do not use Auto Mode, just the Furnace.
When the furnace turns on, I hear a relay click on the main A/C, even though I have power turned off to the A/C at the breaker box, because I only want the furnace fan "pushing" the air, the A/C is too loud.
My questions:
1. Is this relay energizing because it also deals with the automatic mode at the thermostat to cycle between A/C and Heat?
2. If the relay goes bad, will the furnace still turn on?
3. Is there a way to separate the A/C from the furnace so they are two independent systems?
Thank you

**Flybob** · 11-25-2018, 10:36 PM

There are two operation selections on the thermostat. One for operation that is either heat/cool/auto. There is also a fan setting that is Hi/Lo/Auto. With the fan in Hi or Lo the AC circulation fan will run ( no compressor). As you have the breaker off for the AC the fan is not getting power just the control relay. Set the fan to Auto and it will stop.

**Bama Rambler** · 11-26-2018, 11:51 AM

Post the make and model of the thermostat as well as the furnace and A/C and we'll be better able to answer your questions directly.

1) If you have the dometic digital thermostat it has electronic communication to the control box where there are relays for the A/C fan and a triac for the furnace control. So even if the breaker to the A/C is completely off, there still has to be 12 volt power to the control box to operate the thermostat and relays.

2) No.

If the relay that controls the furnace stops operating, the furnace won't operate.

3) Yes

. You can buy a furnace only thermostat and mount it near the furnace and reroute (rerun) the control wiring from the furnace to the new thermostat.

formerFR · 11-26-2018, 11:55 AM

If you don't have the 'FAN' setting on AUTO, then it's quite possible that the Thermostat is trying to turn on your roof air conditioner Fan, even though you have it's breaker tripped. The Thermostat works off of 12v, and the switch to the roof fans the same, even though they OPERATE off of 120v.

Move the Thermostat FAN setting to AUTO...and you'll have no more issues. The roof fans are NOT going to operate under this setting, since you will have only the FURNACE on.

2nd House · 12-01-2018, 11:01 PM

A little confused here.

My choices for Zone 1 are:
Auto, Furnace, Fan, Off, Cool
The Fan choices are: Hi, Lo, Auto

Here are the current settings:
The Mode is set to "Furnace"
The Fan is set to "Auto"
The AC circuit breaker is Off

The AC relay clicks, and the furnace / fan turns on.
When the camper gets to the set temperature on the thermostat, the AC relay clicks, the fan continues for a specified time setting, and then the furnace / fan stops

I believe I will have the relay clicking regardless of either fan setting on Auto, Hi, or Lo. So I might as well keep it on the Hi setting to get as much air as I can. I think the Auto Fan setting is to cycle between either Hi or Lo fan ouput...but that's just a guess.
I suppose (the clicking relay) is fine, as long as the relay continues to work, if the relay goes bad, then I'm guessing, I wont have either AC, or Heat.
Which is why I like the idea of having two separate controls, one for heat, and one for the AC, thereby bypassing the control relay all together, for heat, with it used only to control the AC
Thoughts?
One other question: Does anyone know, just exactly where that control relay is...with out having to climb a ladder and try to find it when it cycles?
Thanks for the help

2nd House · 12-01-2018, 11:09 PM

Quote:

Originally Posted by Bama Rambler

Post the make and model of the thermostat as well as the furnace and A/C and we'll be better able to answer your questions directly.

The AC and Digital thermostat are Dometic...I'm not entirely sure the make of the furnace, but it too is a typical gas furnace.
I believe the main zone 1 AC is 15K BTU, and the bedroom zone 2 is 13K BTU.
Only in Zone 1 is "Furnace" available
I haven't had much success finding a model number of the thermostat.
I found one on Amazon (that looks like it) called the "Duo Therm Comfort Control 2"
Thanks for the help

**Bama Rambler** · 12-02-2018, 02:28 PM

Quote:

The AC relay clicks, and the furnace / fan turns on.
When the camper gets to the set temperature on the thermostat, the AC relay clicks, the fan continues for a specified time setting, and then the furnace / fan stops I believe I will have the relay clicking regardless of either fan setting on Auto, Hi, or Lo. So I might as well keep it on the Hi setting to get as much air as I can.

This operation is completely normal, and you're right that the relay will operate no matter which mode or speed the A/C fan is in.

Quote:

Does anyone know, just exactly where that control relay is...with out having to climb a ladder and try to find it when it cycles?

The relay is in the control box in the air return of the air conditioner. If you pull the cover off the inside the A/C you can see the control box.

You may also like: