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Discussion Starter #1
I recently connected a Venstar T1100 wireless thermostat to my Carrier 58STX070 gas furnace. When I have the thermostat set to heat, and the heater running, the HVAC system will randomly switch over to Air Conditioning and blow freezing air. This is not fun when waking up at 3am with the room at 60 degrees.

The receiver end of the Venstar (T1100REC) will show the heater light on when the heater is running. When it flips out and goes to A/C, the heater light is off and the main power light is very dim. The only way to get the A/C to shut off is to pull the receiver off of it's base, which disconnects the wires from the base that lead to the HVAC system. I then re-seat the receiver and the heater works again.

There are 4 wires for the HVAC: Red, White, Yellow, and Blue (labeled G). The previous thermostat (Honeywell), had a jumper from the Rc terminal to the R terminal (wiring photo here). The new thermostat only has one R terminal (wiring photo here). The Venstar manual has a diagram that shows how to hook up a 4 wire system, and I've followed those instructions.

Anyone here have any insight as to what could be causing this? And, what can be done to fix it? I'd hate to reconnect the old Honeywell thermo because it is downstairs and the heater would never turn off on it's own. It would never get warm enough downstairs; the furnace is upstairs and most of the heat stays up there.
 

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Discussion Starter #3
Why someone would want a wireless thermostat:
To control the temperature in the room that the individual is actually in. Rather than controlling the temperature of the hallway downstairs that the individual is not currently in.
I don't think that's too difficult to comprehend.

Thank you for the obvious solution to the issue... however, I'd like to see if anyone else would have a more constructive answer for me.
 

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flipping slumlord
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Why someone would want a wireless thermostat:
To control the temperature in the room that the individual is actually in.
Do you have duct dampers this opens/closes to direct the tempered air away from the hall or other rooms when you're not in them? That's way cool.

What do you do when someone else is in the other area...
and they want to be warm/cool as well?
 

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HVAC Tech/Owner
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Why someone would want a wireless thermostat:
To control the temperature in the room that the individual is actually in. Rather than controlling the temperature of the hallway downstairs that the individual is not currently in.
I don't think that's too difficult to comprehend.

Thank you for the obvious solution to the issue... however, I'd like to see if anyone else would have a more constructive answer for me.

For the reason you describe.....you are also controlling the temp of the hallway downstairs :laughing: No matter where the thermostat is! I guess you can carry it wherever you go.

I have to remember this one....instead of recommending duct changes to fix airflow problems I'll just recommend they get a thermostat to carry.

Did you set the dipswitches correctly?
 

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Discussion Starter #6
The downstairs rooms would only get warmed up enough if all vents upstairs were closed and the heater was running for hours on end. It's a 25 year old house that is poorly insulated (I'm working on that issue, but just moved in). When we're downstairs, we have the fireplace going to help heat the surrounding area.

Yep, all dipswitches are set as the manual instructed for a gas furnace... all equipment switches are set to OFF.
 

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Fire places are great at sucking in cold air in the back rooms for make up air creating a negative pressure in the home that sucks in even more cold outside air then spiting out the heated air up the chimmney.
Want any real heat from it use an insert or air tight wood stove.
 

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I think your gonna need to install 2-250 watts resistors.

But first, reset all of your dip switches. if it stops doing it, then one of them ws not fully off. If it continues, install the resistors.
 

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Discussion Starter #10
After resetting the dip switches, I shot an email to Venstar support. They said the C (24v common) wire had to be connected. C is not required when you have a thermo that is battery powered. The Venstar is not battery powered.

This wire was not extended from the furnace to the thermo location, but was available at the furnace. I moved the wireless thermo base to FAU closet with the furnace, so that I could connect the C wire. The heater worked well last night, without switching over to AC randomly.

Thank you all for responding to my post, appreciate the help.
 

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That Venstar is a power stealing thermostat. Its in their own install manual that without a C, you may need to use the resistors.

Using a common is better though.
 
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