fan speed question using the "cont" spade connector on furnace control board

[gateman]

Tempstar D90 furnace using Honeywell furnace control board.. I have a 4 speed
blower that has the motor tap for hi (black) on the "cool" spade connector and
the tap for med hi (orange) on the "heat" spade connector, nothing is attached to the "cont" spade connector and the med lo (blue) as well as the lo (red) are connected to the "unused" spade connections..
So, my question is, Can I tap the low speed (red) to the "cont" spade connection? That way I can have constant low speed blower for the newly added IAQ hardware? Thanks...

[Chris_Worthington]

Thread relocated to tech to tech residential.

[timebuilder]

Tempstar D90 furnace using Honeywell furnace control board.. I have a 4 speed
blower that has the motor tap for hi (black) on the "cool" spade connector and
the tap for med hi (orange) on the "heat" spade connector, nothing is attached to the "cont" spade connector and the med lo (blue) as well as the lo (red) are connected to the "unused" spade connections..
So, my question is, Can I tap the low speed (red) to the "cont" spade connection? That way I can have constant low speed blower for the newly added IAQ hardware? Thanks...

Are you a technician working on this, or are you the homeowner?

[gateman]

Actually, I am an electrical engineer, I am working on system integration with
existing old hvac equipment... We do automation and various controls in many
different fields.. We have hvac guys for the mechanics.. So, do you know or just
being difficult, why waste the time posting if you have nothing to add?? I just thought some of guys have ran across this type of furnace control board before..

[atoztech]

No offense but poor attitude. Your an electrical engineer? Is there a schematic at the unit? If so you should have no problem reading it.

[gateman]

electrical schematic only shows wiring paths NOT board logic, the ladder diagram list it as a n/o switch that closes the path when in heat mode or closes
the path in cool mode, the n/o contact for the switch labeled "cont" appears to be 'made' whenever there is no call for heat or cool.. Just wanted to verify if anyone done this in the field?? Not trying to be difficult, just looking for see if this is how the furnace control board logic works.. Does anybody have anything useful to add.. I am sure someone else has ran across this before.. Just trying to electrically integrate several systems of different mfg. and don't
want to damage the little furnace control board needlessly.:censored:.. thanks

[nehvacman]

That "CONT" tap will be powered any time the COOL and HEAT taps are not powered. So basically the fan will run all the time.

[ironpit]

Use your meter to assist you in understanding the logic of the board if you don't know the logic. It may take awhile, but it is safer than guessing, as you can see the the sequence of operation as well as assure the proper values of the circuit you are testing. I went to radio shack and purchased diodes to make my own "flags" for helping me "see" the logic of units I have had trouble with.

[gateman]

Use your meter to assist you in understanding the logic of the board if you don't know the logic. It may take awhile, but it is safer than guessing, as you can see the the sequence of operation as well as assure the proper values of the circuit you are testing. I went to radio shack and purchased diodes to make my own "flags" for helping me "see" the logic of units I have had trouble with.

good idea.. Ladder logic diagrams are the way to go, much more in-depth as to board logic... Schematics are just simple road maps for wire paths..


Thanks for the conformation, nehvac

[CAtech1986]

My thought was that the cont terminal was the designated speed for when there is only a g call from the thermostat. older thermostats will not call for g (fan) during a routine call for heat or cool. new heat pump thermostats will call for g during heat and cool but not emheat. so therefore if you are using the honeywell IAQ and want a specific speed for a dehum or humidify call, uv light, or even just a low speed for the circulate option then you should be able to wire it to cont but... if your tstat calls for g during cool (that can be modified) then it will be at the speed you choose you cont. i do not believe that it will run all the time without a call for g. no furnace does that. no worries best of luck

[ironpit]

don't always have diagrams and works best on the simplest systems. The ladies think the little lights are cute!

[nehvacman]

i do not believe that it will run all the time without a call for g. no furnace does that. no worries best of luck

I think this furnace will.

Give it a try and let us know.