I have a Comfortmaker EF series handler AC/Electric heat. For the past 2 months the blower has been pulsing on/off out of nowhere. It may do this 3 or 4 times then stop. Sometimes it does it then runs for 5 to 10 minutes. My first thought was the thermo was going. Well Ive been wanting to install a progammable one anyway. This weekend I installed thinking that all would be good. Nope... same thing. Even when the thermo is in the off position the blower will go on-off----on----off-on-off-on-----.. lol This may only happen a dozen times a day and can't reproduce on demand. It does seem to be worse on warmer days... This unit is in the attic. My thought is now that the fan control board must be bad? BTW the wiring checks OK. Am I going in the right direction? I found one online for a decent price

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Originally Posted by geeserteg

I have a Comfortmaker EF series handler AC/Electric heat. For the past 2 months the blower has been pulsing on/off out of nowhere. It may do this 3 or 4 times then stop. Sometimes it does it then runs for 5 to 10 minutes. My first thought was the thermo was going. Well Ive been wanting to install a progammable one anyway. This weekend i installed thinking that all would be good. Nope... same thing. Even when the thermo is in the off position the blower will go on-off----on----off-on-off-on-----.. lol This may only happen a dozen times a day and can't reproduce on demand. It does seem to be worse on warmer days... This unit is in the attic. My thought is now that the fan control board must be bad? BTW the wiring checks ok. Am I going in the right direction? I found one online for a decent price

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You first need to find out exactly what is causing the pulsing. In order to do that you need to hook an electric meter up to the wiring going to the blower motor and when the pulsing starts you need to see if the power supplied to the motor is pulsing OR if the motor itself is pulsing with power being applied all the time while it is pulsing.

It is possible the motor is going off and on due to a weak internal motor overload or a defective capacitor. Once you find out that info you will gain the proper knowledge as to which exact part to replace. Just replacing parts without exact testing is a very expensive way to do repairs.

Also with electric heat a possibility exists that the heat sequencer that operates the electric heaters AND the blower motor could be defective causing the motor to pulse on and off.

Thanks for the reply!

The problem is how many times it does it... In this case to be in the attic at the very moment will be next to impossible. I can't reproduce the problem and it happens randomly. The system is obviously not getting a signal from the thermo to start. I completely unhooked the thermo when I was home for the day. Still started. That said the cap isn't the prob since no signal is being sent for the blower to start and not once on a typical thermo generated cycle does it pulse.

As for the heat sequencer. The diag for this circuit show a control board that controls the blower but also has a plug for the heat assy. The heat assy consists of 2 limits, three relay switches one for each coil. Are the 3 switches the sequencers? So is it possible for one of these shorting and signaling the system to turn the blower back on?

Im still focusing on the control board it self.