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dhawth · Apr 14, 2009, 07:54 PM

I have a Comfortmaker Furnace (approximately 1998/99) what is the function of the capacitor as it relates to the furnace operation

MarkwithaK · Apr 14, 2009, 07:58 PM

You could have asked this in your previous post... but in answer to your question the capacitor is basically an energy storage device. In your situation, the cap helps the blower motor along so as not to draw excessive amps.

dhawth · Apr 14, 2009, 08:02 PM

Sorry about that... this is my first time on the site. That was a great answer now I understand. I will start with the cap and see how things go. Thanks again for the help. Good night

MarkwithaK · Apr 14, 2009, 08:05 PM

No problem and come back anytime.

KISS · Apr 14, 2009, 08:07 PM

There are 3 types of motors used: 1) Capacitor start, 2) Capacitor run and 3) Capacitor run, Capacitor start

In Capacitor start, the cap is effectively acts as a short briefly when power is applied. This energises the start winding which causes the motor to start to rotate.

In Capacitor run, it provides a phase shift for the windings, so the motor can turn.

Usually these motors are called PSC (permanent split capacitor) motors. These are the same type motors used in ceiling fans.

This explanation has a few flaws in it, but it's basically correct. I failed to include the induction motor vs. the PSC motor.

There is a law so to speak that says: "The voltage across a capacitor cannot change instantaneously" Hence the short circuit behavior. Some of the fundamental relationships are here: http://www.ep2000.com/Templates/powerquality/DVDT.pdf

Mark kind of has it right.

MarkwithaK · Apr 14, 2009, 08:12 PM

Eh he is dealing with a blower motor on his furnace... figured the simplest explanation would suffice.

ceilingfanrepair · Apr 17, 2009, 10:55 PM

It may have been simple but it's kind of a stretch. PSC motors are generally more efficient than shaded pole, but the capacitor doesn't LITERALLY prevent it from drawing more current.

KISS's explanation was better.

MarkwithaK · Apr 18, 2009, 08:58 PM

Never said KISS' explanation wasn't better. Based upon the OP's related thread I knew why he was asking this question and also knew that there was no need to get into a detailed theory of operation for a capacitor let alone the efficiencies of a shaded pole or PSC. I knew he was curious because of the problem with the blower motor on his furnace and in the long run my basic explanation gave the OP the understanding of the cap.