Easy question

[eeprom]

Hello all,
I'm an electrical engineer, not an HVAC person. And this question might be too easy for this forum. I wouldn't waste your time here, but it's about impossible to get a manual for a home furnace. And if you call the manufacturer, they won't give you tech support unless you are a contractor, even if you paid for the heater.

So, here goes.... My furnace control board died and I replaced it with a substitute Honeywell board. My original board is no longer made. I wired it up and everything works fine, except now my blower fan runs continuously at a low speed. It only goes to a high speed when the heater comes on. This low speed continuous running is new to me.

I traced this back to a terminal on the control board named CONT (which, of course, means continuous). That terminal is hot for all conditions. And according to the schematic on the door, it is supposed to make the blower run at all times except when the heater is on. When the heater is on the blower motor is energized at a higher speed. Otherwise the motor runs at a lower speed through the CONT terminal. If I disconnect the CONT connection, the heater works exactly like it used to.

So, what's with the CONT connection? What's the purpose of this? Is it optional? Can I leave it disconnected?

Thank you for humoring me.

EE

 

[itsmoked]

It's point is to provide either continuous filtration or to keep the conditioned space homogenized. Consider a room in the conditioned space that has a lot of solar gain. That room could become very hot while other rooms remain cold. Conversely that same room could get very cool at night but the thermostat mounted back by the furnace at the return won't know about that cold or roasting room without the air being brought back to be sensed.

There is another mode often provided by thermostats that has the system change from standby to circulate for 5 minutes every thirty just to sense those remote spaces.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LittleInch]

Define "blower fan".

Do you mean a fan which blows warm air around the building or the fan which blows air through the furnace which then goes up the flue?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IRstuff]

Isn't this more of an ASHRAE requirement compliance thing? Ostensibly, even a residential building requires a minimum of 15 cfm of air flow, regardless of whether you want to heat or cool; therefore, you have a continuous fan setting to provide the indoor air quality (IAQ) desired.

https://www.epa.gov/indoor-air-qual... called the American,air per minute (cfm) per

TTFN (ta ta for now)
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[GT-EGR]

Another reason for continuous air movement somewhat already covered above is if the furnace is responsible for delivering outside air (ventilation air) to the rooms it’s connected to.