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pwstick · Jul 20, 2005, 07:42 PM

I have a Lennox Pulse furnace that is approximately 16 years old with central A/C. Last summer the blower motor stopped running while using air conditioner. Determined that the blower relay was bad, replaced and it ran fine through to this summer season. Again the blower relay contacts failed, replaced and it ran this time for approximately two weeks and the blower motor stopped running again.

All indications are showing that the relay contacts have again failed. Blower motor is 3/4 HP and relay is rated for 3/4 HP@125VAC. When I jumper across the relay contacts, the blower motor seems to run normally. I do not have an amp clamp to check the current of the motor. Could the capacitor be causing the relay contacts to continue to fail?

labman · Jul 20, 2005, 08:56 PM

Capacitors are hard to check without a capacitor checker. You can do a rough check with a volt meter on a big one, but that is only useful for a dead one that keeps the motor from starting. A 3/4 relay for a 3/4 motor is marginal. You may be having trouble with it on A/C because it uses a different winding for higher speed. The motor could be on its way out and drawing excess current. Oil or grease it if it has ports for it. I would pick up a slightly larger relay, and see how things go.

labman · Jul 20, 2005, 09:18 PM

Another thought. Is it the contacts that fail, or does the coil fail to operate the relay? Can you feel or hear it work? If not, you may want to check the voltage to the coil. Should be about 24-25 volts.

pwstick · Jul 21, 2005, 03:57 PM

Thanks! I also was wondering about the rating of the relay contacts not being high enough but forgot to think about the speed being higher for the A/C setting. There is 24VAC consistently at the coil when the blower needs to run, definitely the contacts that seem to be the problem.

I'll try a larger rating for the relay contacts and do some PM on the blower motor.