[artbuc]

I have two Bryant induced draft gas heaters with AC. Thermostats are 4 wire round Honeywell. My downstairs heater has a resistor across the W(heat) and C terminals on the control board whereas my upstairs heater does not have this resistor.

What is the resistor for and why would one unit have it and the other not? Thanks.

 

[Doc Holliday]

pics?

 

[artbuc]

pics?

Will get a couple. BTW, the reason I am interested is because I was looking at wireless thermostats and came across a discussion about power sharing by connecting a resistor from W or Y to C depending on what type of problem you have. I looked at my units and saw the resistor on one and not the other - got my curiosity riled up.

 

[Doc Holliday]

Power sharing is used when another device is used in co-ordination with the stat or at least that's what I've gotten from recent research. I can't say I'm knowledgable about any of it.

The Uponor thermostat
requires a minimum current to
operate correctly. A 1,000 Ohm,
0.5 Watt resistor is included in this
package and may be required for​

operation of third-party devices.

 

[Doc Holliday]

However, some
commonly used third-party devices
(e.g., relays, zone valves, etc.) may
have compatibility issues with the
thermostat. If connecting the
thermostat to a third-party control
device, refer to that device’s
installation instructions for specific
information regarding operation​

with a power-sharing thermostat.

 

[artbuc]

Here it is:

 

[JJboy]

I have two Bryant induced draft gas heaters with AC. Thermostats are 4 wire round Honeywell. My downstairs heater has a resistor across the W(heat) and C terminals on the control board whereas my upstairs heater does not have this resistor.

What is the resistor for and why would one unit have it and the other not? Thanks.

This resistor is reducing the current. Don't ask me why

The control board has the same rev?

 

[artbuc]

This resistor is reducing the current. Don't ask me why

The control board has the same rev?

I don't know if the resistor is reducing current going to the board thru W by leaking some to C or increasing current thru R to the thermostat or both.

 

[JJboy]

I don't know if the resistor is reducing current going to the board thru W by leaking some to C or increasing current thru R to the thermostat or both.

Test... R-C > W-C

 

[beenthere]

Post model number of thermostat. It may be a power stealing thermostat. And many control boards have problems with those stats, unless you use a resistor like that.

 

[artbuc]

Post model number of thermostat. It may be a power stealing thermostat. And many control boards have problems with those stats, unless you use a resistor like that.

Beenthere, both of my thermostats are original (21 years) and they are the basic round Honeywell's - 4 wire with 1-stage heat and 1-stage cool. The only power they use is in the heat anticipator.

http://www.google.com/products/cata...jq0gHk0NyaDg&ved=0CD4Q8wIwBg&biw=1003&bih=638#

 

[beenthere]

If you have the CT, instead of the T model thermostat. Then you have power stealing thermostats. And the resistor is required on most installs.

 

[artbuc]

If you have the CT, instead of the T model thermostat. Then you have power stealing thermostats. And the resistor is required on most installs.

They are T87F with mercury switches. The link was for picture only. Did Honeywell make the CT87F's 21 years ago? Anyhow, what's up with the resistor?

 

[beenthere]

Digital thermostats have been around for 20 plus years.

Good chance someone had installed a power stealing at one time, and then removed it later.

 

[artbuc]

Digital thermostats have been around for 20 plus years.

Good chance someone had installed a power stealing at one time, and then removed it later.

Interesting. I bought the house brand new and all of the HVAC equipment, including thermostats, is original. I wonder if the resistor is factory installed?

 

[yuri]

No. The replacement circuit board does not come with it or ask for it. Probably the installer wanted to change the length of the heating cycle and added the resistor. Causes more current flow and affects the heat anticipator/cycle. I would NOT use it with any new tstat. Lots of those old Bryants have cracked heat exchangers. Usually crack around the dimples inside.

 

[beenthere]

Not that I have ever seen before.

 

[artbuc]

No. The replacement circuit board does not come with it or ask for it. Probably the installer wanted to change the length of the heating cycle and added the resistor. Causes more current flow and affects the heat anticipator/cycle. I would NOT use it with any new tstat. Lots of those old Bryants have cracked heat exchangers. Usually crack around the dimples inside.

Yep. I figure it is a heat anticipator fix, although I can't understand why it is needed.

I know these Bryants have some issues with delamination of the secondary lining but I did not know about the primary failures. Is there anyway I can check for a cracked xchanger or do I need a pro with a camera or CO detector (or something)?

 

[yuri]

The mid efficiency have that problem, the highs don't seem to.

 

[artbuc]

The resistor is 1k ohms which means it is leaking 0.024 amps to ground. Since the heat anticaptor adjustment range is 0.12 - 1.2 amps, I can't imagine what this small amount of current leakage is doing. I am not going to replace the thermostat on this unit so I guess I will leave the resistor there considering it has been there for 21 years. Thanks to all who responded.