RV.Net Open Roads Forum: Tech Issues: New Thermostat Question

RV Blog

  |  

RV Sales

  |  

Campgrounds

  |  

RV Parks

  |  

RV Club

  |  

RV Buyers Guide

  |  

Roadside Assistance

  |  

Extended Service Plan

  |  

RV Travel Assistance

  |  

RV Credit Card

  |  

RV Loans

Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > New Thermostat Question

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 3  
Next
Sponsored By:
NRALIFR

Truck Camping Out West

Senior Member

Joined: 11/27/2005

View Profile



Posted: 01/18/21 09:15am Link  |  Quote  |  Print  |  Notify Moderator

I have this furnace in my TC.

[image]

There are only two connections to the thermostat, and they are labeled “Thermo” and “+Thermo”

[image]

I’m installing a new thermostat, and it’s connected like this. G is connected to G, and W is connected to W.

[image]

Both the AC and furnace work as they should. The issue I’m wanting to resolve is the FAN switch on the t-stat doesn’t turn the furnace fan on when it’s in the “On” position. It behaves as if the FAN switch is always in “Auto”. I would like to be able to manually turn on the furnace fan, if that’s possible. I don’t need to control the AC fan manually.

The original t-stat was a mechanical type, and I can’t remember if it had a fan Auto/On switch or not. I suspect it didn’t. I replaced the mechanical stat many years ago with a RiteTemp digital programmable model. The new t-stat had the ability to wire the fan Auto/On switch so that it would function as a Hi/Lo switch, which I did. The AC has a two-speed fan, but the furnace doesn’t. I found that I never used the High fan speed though, because the AC will freeze us out on low.

The buttons on the RiteTemp have gotten difficult to use, and we never use the programmable function of it, so I’ve replaced it with a non-programmable model.

The way this was all installed by Lance, is the “Thermo” and +Thermo” wires, that are clearly labeled on the furnace pigtail, were run to the wall t-stat location. I’ve verified with a VOM that the two blue wires in this plug:

[image]

Are these two wires behind the wall t-stat.

[image]

As you can see, they aren’t connected to the t-stat. They are connected to the pink and purple wires in the 8-wire cable, which runs up to the roof AC. I assume they run through a relay in the AC to prevent the furnace and AC being turned on together.

Is there a way to wire the furnace to the wall t-stat so that the Fan Auto/On switch will turn the fan on manually?

[emoticon][emoticon]


2001 Lance 1121 on a 2016 F450


dougrainer

Carrolton, Texas

Senior Member

Joined: 06/11/2007

View Profile


Offline
Posted: 01/18/21 09:23am Link  |  Quote  |  Print  |  Notify Moderator

NO. RV Furnace fans CANNOT be operated by itself. Once the Furnace fan comes ON, then the ignition sequence happens. ALL the 2 wires do is transmit the 12 volts TO the furnace to start a Heat cycle. Nothing else. When you ask for heat, the wall tstat sends the 12 volts TO the furnace and then it operates until the Wall tstat is satisfied. Doug

BFL13

Victoria, BC

Senior Member

Joined: 02/15/2006

View Profile



Posted: 01/18/21 09:32am Link  |  Quote  |  Print  |  Notify Moderator

You are asking for the fan to run but not have the gas/ignition sequence to follow. I suppose you could run parallel (? a second set anyway) wires to just the fan part, by-passing the circuit board etc, with a switch on those wires so just the fan would run.

Can't you run the A/C fan now without turning on the A/C? ISTR that is available to just circulate the air.


1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

NRALIFR

Truck Camping Out West

Senior Member

Joined: 11/27/2005

View Profile



Posted: 01/18/21 10:02am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

You are asking for the fan to run but not have the gas/ignition sequence to follow. I suppose you could run parallel (? a second set anyway) wires to just the fan part, by-passing the circuit board etc, with a switch on those wires so just the fan would run.

Can't you run the A/C fan now without turning on the A/C? ISTR that is available to just circulate the air.


Correct. It would be advantageous to be able to run the furnace fan without the furnace producing heat when I’m heating just with electricity. The furnace also heats the black and gray tank area, and when the temps get down in the teens and lower, I have to make sure the furnace runs once in a while so the dump valves don’t freeze.

The way things are installed right now, neither the AC nor the furnace fan will turn on manually.

Thanks.

[emoticon][emoticon]

NRALIFR

Truck Camping Out West

Senior Member

Joined: 11/27/2005

View Profile



Posted: 01/18/21 10:03am Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

NO. RV Furnace fans CANNOT be operated by itself. Once the Furnace fan comes ON, then the ignition sequence happens. ALL the 2 wires do is transmit the 12 volts TO the furnace to start a Heat cycle. Nothing else. When you ask for heat, the wall tstat sends the 12 volts TO the furnace and then it operates until the Wall tstat is satisfied. Doug


Thanks Doug. I had a feeling that’s what the answer was going to be.

The new digital t-stat should do everything I need it to do, without the added complications of having to override the programmable functions that the RiteTemp stat wanted to default to.

I thought I needed a programmable t-stat and the two-speed fan control at one time, but discovered after using it for several years that I really didn’t.

It’s a nicer looking thermostat too.

[image]

[emoticon][emoticon]

* This post was edited 01/18/21 10:09am by NRALIFR *

BurbMan

Islip, Long Island

Senior Member

Joined: 09/20/2001

View Profile



Good Sam RV Club Member


Posted: 01/18/21 12:28pm Link  |  Quote  |  Print  |  Notify Moderator

I just replaced the circuit board in my Atwood furnace and Doug is correct...where the T-stat wires connect to the board, closing that circuit starts the ignition sequence. However, on my board there were 2 separate terminals for fan and 12v+. As part of my troubleshooting, I could apply 12v directly to the fan terminal and get the fan to run.

So you could in theory run a separate wire to the fan terminal on the board that you could control by a switch. Even if you couldn't get the wire back to the T-stat, you could a mini slide switch or similar close by the furnace.

The fan would then get 12v either from the thermostat powering the board to start the ignition sequence, or directly from your bypass circuit that only powers the fan.

One of the reasons for the factory set up is that the a/c fan runs on 120v, so when you have shore power you can leave the fan on as long as you want, no issues. The furnace fan runs on 12v and consumes a lot of wattage. Overriding the furnace fan in the "on" position when boondocking will kill your batteries in very short order....


2015 Ram 3500 SRW 4x4 Laramie Crew Cab Long Box, Cummins diesel
2002 Lance 811 Slide-In Camper
SOLD: 2008 Terry 34' TT
SOLD: 2001 K2500LT 8.1L Suburban

Lance 811 Renovation Story!
Project Complete!
Maiden Voyage!


NRALIFR

Truck Camping Out West

Senior Member

Joined: 11/27/2005

View Profile



Posted: 01/18/21 02:38pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks Bman, I’m going to look into doing that. I would only be using this when we either have shore power, or I leave my Yamaha 1000 “buzzing away all night” to provide power for extended periods. All that’s needed is to keep the waste tanks above freezing.

If I do this, it will of course have a separate on/off switch. What if I also ran that circuit through a PWM speed control to slow the fan motor down? I doubt it needs to run at full speed to do what I need.

Any comments or opinions?

[emoticon][emoticon]

DrewE

Vermont

Senior Member

Joined: 08/23/2014

View Profile


Offline
Posted: 01/18/21 03:23pm Link  |  Quote  |  Print  |  Notify Moderator

Running an RV furnace fan without the burner operating is not a great idea, in my opinion. The fan motor (there's only one) has two fans attached to it: one circulates air through the RV on that side of the heat exchanger, and the other circulates combustion air through the other side of the heat exchanger. With the burner not operating, you're basically operating the heat exchanger in reverse: cooling the inside air with a steady stream of cold air from the outside.

An auxiliary circulator fan would be a bit better, in that it doesn't actively cool the burner side of the heat exchanger, but you'd still be losing a good bit of heat through it. Probably more useful would be to add a small auxiliary electric heater for the wet bay and circulate the air through the living space of the RV using either the air conditioner fan or a portable fan.





NRALIFR

Truck Camping Out West

Senior Member

Joined: 11/27/2005

View Profile



Posted: 01/18/21 03:57pm Link  |  Quote  |  Print  |  Notify Moderator

You’re right Drew. Thanks for waking me up.

I may be able to accomplish what I need by using one of the settings on the new thermostat. It’s got a “Minimum Cycle Period Adjustment”, that defaults to 12 minutes for gas heat, but can be set for as long as 60 minutes. It’s not hard to change, but I’d probably have to keep a cheat sheet nearby because I’d forget how to do it.

When I’d need it, a single cycle every hour would probably be just enough to keep things from freezing. That setting could also be used when we’re dry camping totally without shore power or generator, and would help minimize the battery usage.

Thanks again.

[emoticon][emoticon]

pianotuna

Regina, SK, Canada

Senior Member

Joined: 12/18/2004

View Profile


Offline
Posted: 01/18/21 05:00pm Link  |  Quote  |  Print  |  Notify Moderator

Nralifr,

Simply replace the return air grill with a twin window fan. Mine draw a scant 27 watts and I control them with a mechanical thermostat near the water pump.

They pressurize the hot air ducts and move just a bit of air. No more freeze ups for me.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 3  
Next

Open Roads Forum  >  Tech Issues

 > New Thermostat Question
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2021 CWI, Inc. © 2021 Good Sam Enterprises, LLC. All Rights Reserved.