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Old 01-14-2012, 09:32 AM   #1
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Lennox Commercial Furnace


I have a Lennox rooftop unit, gas, heat and air. new condenser motor, and new motor for squirrel cage. When the thermostat tells it to heat, the igniter will light the burners, and a couple minutes later the fan comes on blowing heat into house. only blows for a couple minutes then the fan kicks off, but burners remain going. PAAAAAAALease someone with any ideas

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Old 01-14-2012, 10:02 AM   #2
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Is the blower still receiving 240V when it shuts off? Did you replace the capacitor at the same time as the motor? Some of the blower motors were control by circuit board, others a 3 prong limit and others by a dial type limit. Follow the wiring diagram and locate the control.

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Old 01-14-2012, 10:06 AM   #3
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Has new cap. Have no meter. Does have a dial control with 3 settings in degrees(temperature)
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Old 01-14-2012, 10:18 AM   #4
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If you do not posses a VAC meter, you will not be able to safely or accurately trouble shoot your problem (unless you want to start changing a slew very expensive part randomly) you are going to need to call a qualified HVAC service technician.
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Old 01-14-2012, 11:40 AM   #5
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check motor casing is it hot to the touch tripping internal or as said capacitor...try stat in FAN/ONLY setting if motor stay on it's not that...is there a control module for the heating side within the unit black relay on board...controls the fan in heating ON call might be dropping out...
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Old 01-14-2012, 11:53 AM   #6
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When fan trips off, u cannot jumper it to get it back on. I hafta wait a bit, till some safety feature kicks back out before it allows me to jump it to kick back on. I did notice when replacing the thermostat that it was wired with the white and red reversed. White was wired as jumper. Red was connected to white wire location. So when i jumper white and yellow the fan comes on. When i jumper the red and white the burners ignite and fire up. Is this normal??? I can jumper to make system come on, but fan still only runs a couple minutes before bein locked out for (x) amount of time
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Old 01-14-2012, 12:06 PM   #7
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It sounds like a high temperature limit switch is tripping and cutting the gas off and keeping the fan on as that is what it's supposed to do, remove any excessive heat without making any more. Then it's resetting and allowing you to control it again.

Model number would help so we could find a manual.
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Old 01-14-2012, 12:07 PM   #8
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Red is the R terminal on a subbase in the real world White is the heat side of the system.R to G is straight fan on a jump(same as you doing FAN/ON from the stat).do you see a subbase jumper on the Rh to Rc the RED from wall goes there....before changes check what the connections are up on the unit especially that Red/R.keep in mind the FAN cycle is thru the heating side of the system not the thermostatNOTE when disconnecting that RED either end don't spark it on any metal if the TR isn't/most aren't fused you'll ace the TR on the 24V side...$$
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Old 01-14-2012, 12:12 PM   #9
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don't rely on the colors of the wires, use the labeled terminals

R-24 volts/control power
W-heat
Y-cool
G-fan

so jumping the R terminal to the W terminal should bring on heat, regardless of what wire color is there.
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Old 01-14-2012, 03:53 PM   #10
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Motor for squirrel cage gets really hot, then turns itself into thermal protection and shuts off. Motor still gettin 220/230. Does that mean motor is no good?? Motor isn't very old. Do they usually hava warranty??? Could it be a different issue???
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Old 01-14-2012, 05:16 PM   #11
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What happens in "fan on" and "cool" mode?
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Old 01-14-2012, 06:37 PM   #12
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Didnt try. My fan limit switch has a built in switch on it where u can turn on specifically that fan motor alone. Didnt try it in other ways. I kno that motor gets warm too fast, then puts itself into protect mode
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Old 01-15-2012, 07:59 AM   #13
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Post a model number and we can look up the motor to see if it's the correct one.
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Old 01-15-2012, 08:16 AM   #14
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Was installed feb 22 of last year. Found receipt from the job. Motor should have a one year warranty shouldnt it??
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Old 01-16-2012, 08:17 AM   #15
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How long is the warranty on a fan motor???

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