How do I bypass a fan relay circuit board on an AC air handler?

Question

My AC is not blowing air it seems because the control board is fried, the board has a fan relay which has 3 connectors, "SPT", "NO", and "NC", is there anyway to make the fan work by putting together any of the cables that connect to the relay, like the NO and the NC? I have ordered a new board online (HK61EA006) but in the meantime I am burning in Tucson, please help...

Answer 1

HVAC Tech.:   DON"T DO IT!!! You could fry the blower motor, That is a multiple speed blower. If you cross the wrong wires, in a flash your motor could be gone ,Compounding an already bad problem. I don't order parts on the "NET" there are many local supply Houses that stock parts so repairs can be affected in minutes or hours instead of days and weeks. Have you tried those???  You can't go by wire colors as motor may have been changed and color would mean nothing. you need meters and drawings to attempt field changes. They are all UNSAFE and could result in your house burnning up as well.

Answer 2

WOW, yes maybe you can depending if it is only the relay on the board that is bad and not the printed circuit itself that provides the power to the relay.

I have done it.

I really really hate to try to advise anybody without looking at the schematic myself and putting a meter on it to verify.

But the "SPT" designation doesn't make sense to me. That likely means it is a Single Pole Single Throw relay and that connection should be your common, your power for the relay.

Then NO connection means "normally open" and the NC means "normally closed".

If you have a SINGLE relay and the air handler is not a furnace and has no heat function and the fan motor has a SINGLE motor speed tap then:

Normally Open, means this contact is open when not powered. In other words when off. So that is the contact that needs to be closed when you want it to run. Myself, I would verify the spt is the common by checking power to ground, you have to close the blower door safety while checking that.    

So jumping from the common "C" to the NO should power up the fan for a "fan on" relay.

Then your fan should run 24/7 and you will have to turn off the switch on the unit, or shut off the breaker to shut it off.

And for a fan "on" relay the NC is not used on the board.  

BUT if you have a heat function then you likely have TWO relays and the other one is the high/ low for the different fan speed taps.

If that is the case you need a meter to determine which relay is bad AND want to pull the low speed tap off the motor to prevent an error in case the board wants to power up the low speed while you jumpered to the high speed.  

In that case the NO is the high speed for cool and the NC is the low speed for heat.  And again for cooling you want to connect the common "C" to "NO" after pulling the low speed connection from the motor.

But what I told you is the normal situation. No way can I tell without your schematic if yours is not wired strange in some way.

It really shouldn't be attempted by anybody that can't read a schematic well and use a meter.  Even then it is not recommended for even the technicians to "jury rig" things.  

So I caution you against it.

Good Luck.

Answer 3

Thor's right. Jump across the wire on the SPT terminal,. (may be black) to the wire on the NO terminal, (should definitely be black) and blower will run continuously until power is shut down to unit. (NC wire is probably red, maybe blue, and is for the lower blower speeds, used for heat)

Hope this helps.

20+ yrs hvac tech

Black- high speed,    blue and yellow will be mid speeds, red will be low speed, white will be common, capacitor wires will be brown.   These are standard colors for residential blower motors.   If you're not comfortable jumping the motor wires out, by all means, don't do it.  For my own purposes, (Buddy's garage furnace)  I saved him from buying a $250 control board by using an auxiliary relay to run the blower, bypassing the one on the board....but again, to err on the side of safety, if you're not handy, or don't understand the concept, then Johnie is right.

Best of luck.