I have a intertherm model C3QA-054U-B. The blower stays on at a low speed all the time. If I put the thermostat on vent. the blower speeds up. If the a/c kicks in the blower speeds up. the only way I can make the blower stop is to turn the breaker off. Is there anything I can look at to check this out?
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This is a diagram of a blower relay and a fan motor, the normally closed fan relay switch goes to the low speed which is the Heat speed, the low speed is controllled by a temperature delay depicted in the low speed circuit.
The normally open fan relay switch goes to the high speed, which is the AC modes speed , also if you run the fan continuously via the fan switch on the thermostat this is also to high speed.
I suspect the temperature delay's on setting is being reached thus cycling the low speed of the fan.
Do the blower speed settings still work, just weaker? Or is it just one low speed all the time? If you can still change the speeds then it's a weak blower motor. If its just one low speed all the time, (same speed for high and low blower speed settings) then you need a blower motor resistor.
Your blower motor has several speeds to it and by the problem you are having it sounds as though the blower motor may be going out. The motor has a slower speed for the heating cycle and since you have the noise in the heating mode I suggest having the blower motor changed as soon as possible since it could cause other problems in the heating section of the furnace( possibly burning out the high limit switches). Good Luck on your repairs hope this helped
Depending on the model of the furnace, the blower is either a 2 or 3 speed. When the furnace operates in heating mode with the thermostat in the auto position, the furnace starts the fan when the furnace reaches a specific temperature or after a set time delay, but it operates the fan in low or med low speed on heat mode, when you put the thermostat fan switch in the "ON" position, the furnace operates the fan in "HI" speed, the same speed used for cooling mode. You may have a blower moter that is starting to short. I would recommend having a professional replace the motor before now before it becomes an emergency in the middle of the night during a cold spell.
Red= power........White=heat.............Green=fan.................(grey)-(yellow)=cool .....these are the connectons. Disconnect these wires from the thermostat and know that red/power is the only wire that send power to the thermostat, and the rest sends it back to the unit to call for whatever,, red--to . white for heat... red to green for fan .... &red to grey for cool! OK! Turn all your power on, and use a jumper wire from red / green for fan and see if the fan comes on! Then move the jumper wire from red to green , to red / to white for heat and the fan , wait for 3 minutes before removing and going to the next step. Then red /to grey for cool and check if the outside comes on. Either you have a wire touching past the insulations and making a connection, a bad thermostat ,oe excessive wire lead touching the next connection.Thank you very much!