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TimVZ26
TimVZ26, HVAC Technician
Category: HVAC
Satisfied Customers: 157
Experience:  6 Years exp. Nate Cert. in Air-to-Air Heat Pumps, Lots of Bryant/Carrier exp.
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I have a Coleman furnace with A/C. The blower turns on/off

Customer Question

I have a Coleman furnace with A/C. The blower turns on/off interminantly until the cooling setpoint has been reached. The control board is a S1-7990-319P. I have tried different t-stats and am on my second replacement board. This only happens when on "cooling" mode. No problems for heating mode. Any help?
Submitted: 6 years ago.
Category: HVAC
Expert:  TimVZ26 replied 6 years ago.
Chat Conversation Started
TimVZ26 :

Hi there, is the furnace a self ignition type or an older style with a pilot light?

TimVZ26 :

also, does the A/C stay on when the blower motor shuts off, or do they cycle together?

Customer:

No pilot light. The condensor stays on. Only the blower turns on/off.

TimVZ26 :

ok, do you have a volt meter? I am thinking that you may have a blower motor problem, what we need to do next is find out if we are losing voltage to the blower motor, or if there is something else droping out voltage causing the motor to turn off... If you turn the fan switch to ON does the blower run fine?

Customer:

It does the same thing with the switch "on" as it does in "auto". I have wired the motor direct bypassing the control board and it runs continuously - no dropping out. The relay on control board is clicking on/off.

TimVZ26 :

ok, and this is your second control board??? was the first one doing the same thing? and how long ago did you change the board?

Customer:

Yes the other two boards where doing the same thing. I tried latest board today.

TimVZ26 :

ok, do you have a volt meter to check for voltage at the motor???

Customer:

yes

TimVZ26 :

Check for 110 volts at the motor, you should have it when the motor runs....see if we lose voltage when the motor turns off...if we don't then we have a bad motor, if we do lose it then we need to look elsewhere

Customer:

I could check that but the motor runs fine while on "heating" mode. Works fine in cool season just does it when trying to cool. This issue started last summer then went into heating season. Revisiting the problem now back into cooling mode.

TimVZ26 :

ok, you might be using different speeds on the motor, the winding for the heating speed might be fine and the winding for the cooling may be the problem....

Customer:

It is only a one speed motor

Customer:

The relay output clicks on and off

TimVZ26 :

ok, check if you are losing voltage from G to COM on the low voltage connections...if you are losing it there then it is the TSTAT if you don't lose it there then it is the circut board...When the fan runs you should have 24 volts from green to common