Question about Heating & Cooling
I have a lennox merit 10acc system. This morning it turned on however after a minute or so before the fan started to blow air it switched off. 15 minutes later the system turned on again but the same problem repeated itself. Any advice on what the problem may be? thanks
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Posted on Jan 02, 2017
Hello there, I have heard of this happening in my 33 years at repairing residential and now commercial systems. Not to often though. I assume you are in the heating mode as you say that it comes on, the burners, and before the fan energizes on the time delay, the burners shut off? Correct me if I am wrong, as there is a delay on the blower motor to come on until the limit control reaches a pre-determined setpoint in the heat mode. The a/c mode it will start up all at once. Not knowing how old this unit is, I looked it up and it shows its a split system, furnace indoors and condenser outdoor and rather a new unit. A 21/2 ton unit. What can cause this is the thermostat not working properly.This condition you are describing does not happen hardly ever as I mentioned. Now if it were the older lets say 1980's unit with a standing pilot that is on all the time, I have seen them do this from just the pilot flame heat. Not the case hear. I would go to the furnace if it is easy to get to, as some are horizontal in the attic and remove the panels to locate the thermostat wires coming into the unit. They will be incased in a brown cable with a red, yellow, green, blue, white, may be more. They will terminate to a circuit board most likely with screws holding them in place. They are only 24 volts a/c, but I would shut off power to keep from having an accident like shorting out the board. just unplug it. Tighten all connections on this board. You may have a door panel kill switch on a panel you removed that shut off the power for safety. If you do, just make sure you put it back in place right as it will not work at all if you don't. You may not have one. If all looks good there, plug it back in. The stat would be the only thing that would cause this to keep happening, unless you have a thermostat wire touching some where in the wall together with another one. This is unlikely, but does happen. It may be at the thermostat where the wire comes in. Turn power back off and remove cover, Under the cover is the stat. There are 3 sections. Cover, stat, and sub-base. Take a very small screw driver and lossen the screws that you can see, until the stat pulls off. You will know seeing the wiring and sub-base. You will have markings such as W, RC, RH, G, Y. Make sure these wires are not touching anywhere. Tighten down connections. You will see a red wire connecting RC to RH. The is the hot wire for both heating and cooling is all. Put it all back together and wait to see if it continues to do this. If you are saying the fan does not come on at all, you may have a faulty fan motor. If it has come on and blown air you are good. To check it, just set the fan to the on position to see if it starts. If it never comes on, then this blower motor may be the fault, after the unit calls for heat it starts the burners and after the delay it gets a signal from the circuit board and limit to come on and doesn't. This would be a faulty blower motor. Please let me know if I am in the right area of the problem. Excuse the long solution, I just like the person to get a full understanding on what may be taking place, LoL. Please keep me posted and let me know if the motor does run at all. If so, and you have done what I have asked of you, I would pick up a new 24 volt thermostat. This is all it could be except for wires touching.
Posted on Mar 17, 2010
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