Lennox Merit series A/C unit: Thermostat is set to 73 but the unit is not blowing at all. Checked the fuse box on outside unit and main box for possible power surge (Tampa Bay area - afternoon rainstorm season). After fuse reset, the unit started right up, ran a cycle for 10 minutes and stopped. This happened twice over a two hour period, but nothing since.

It will be inside the unit main panel. Turn main power off and remove the main front panel. The fuse will be located on or near the fan control board. Typically they are a flat agc type fuse. 3-5 amps. The problem will be that if the fuse is blown -there is a reason for it. They don;t just wear out and blow. Look for frayed wires around the outside unit and in the thermostat to make sure you dont have a short. Otherwise, you will just blow the fuse you replace.

Sounds to me like you have wiring issues. Need to make sure all your connections are tight, wires are clean and free of bare spots (possibly from rodents chewing them)and your settings on your tstat are correct. Heat pump with back up electric heat.

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HI see if the hotsurface ignitor is glowing by the burner , check the pressure switch also chech air filter is not blocked

I have the same issue with a G21Q4-5-100-1 model lennox. House drops 8 - 10 degrees. I have 3 thermostats and all react the same way. I was told by service tech that the Ignition Coontrol Module is bad and acting intermittanely. ???

At whic step does it sto at and theres your problem. step-1 thermostat calls for heat and vent fan turns on.... step--2 the glow plug or hsi lights ... step-3the main gas valve comes on and heats the box...step-4 when the box heats up it closes a temp. switch to start the main fan motor!

Check to see if there is any board in the outside unit with a fuse .Maybe the fuse popped causing the unit to stop working .
Also check to see if you are getting 24 volts on the thermostat wire going to outside unit .

check to see supply air should be around 58F. 20* difference form supply air to return air if 58F my guess unit under sized air filter clean? when was the last time you had the unit tuned up?

electrical connections @ the furnace may the thermostat .Tom

Sounds like you either blew a transformer, have a bad circuit breaker or blew the main fuse in the outside disconnect. If the indoor unit is still blowing air (no matter what temperature) start looking at the power supply to the outdoor unit. From the circuit breaker, the power will go to a small box located within a few feet from the outside unit. This box will have either a lever on the side or you will be able to open the box and pull out the fuses. From this box the power goes to the condensor. The first thing you should do is to turn off the breaker to the outside unit. Flip it back on and if you have a call for cooling, after about 3 minutes the outdoor unit should start. If it does not, shut off power again to the unit by switching off the breaker, go outside and pull out the fuses in the disconnect box. Using a multi meter, check for continuity thru the fuses. If you have continuity, call your technician. If one or both fuses show no sign of continuity, replace the fuse(s). Make sure that the thermostat is working and sending a signal to the indoor air handler. You may be able to check this by turning the fan switch to "Fan" and see if the blower turns on. You may just have a bad thermostst. Caution should be used anytime you are near electrical components. If you do not have the skill-set required to test electrical equipment, leave it to a proffessional.