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hi i am dan i can help you with this. do you get a flashing error light on the control board when it turns off or is not working?
ok that blinking is an error code. can you count how many times it blinks. example it may blink 3 times the pause and repeat or blink 2 times fast and 3 times slow and then repeat. also i will need the model number of your furnace. it should be on a big sticker on the inside of the furnace.
yes i am just looking up some specs for your furnace can you please clarify that flash code because those are all verry different errors. there should also be a sticker on the inside of the furnace describing the error codes.
ok i was able to find the specs for your furnace. the code is a 13. one fast flash and 3 slow flashes. that means one of the limit switches are opening. first we will need to check a few basic things. first does the blower run and blow air out of the vents? next what is the condition of the air filter and when was it last replaced?
ok does the blower continue to run when it turns off on the error? also check and make sure nothing is stuck in the blower wheel. any restriction to the airflow will cause the furnace to overheat and trip the high limit safety switch.
no you were correct in the error code. that code is 12 that is normal after starting up from turning the power off and back on.
yes after startup you will get that code for 90 seconds and then it will go away and start normal operation
ok do you have an electrical meter to test some components?
ok in order to narrow down the problem we will have to determine which limit switch is turning it off. you will have multiple ones in your furnace. one or 2 around the burners one near the drat inducer motor or exhaust pipe and possible one on the blower housing. they are small 1/2" diameter round switches with 2 wires connected to it. some of them may have a button between the 2 wires to reset it if it is a manual reset switch. you say you worked on the exhaust pipe? make sure the whole exhaust is clear and not restricted.
if you turn the power off to the furnace disconnect the switches one by one and jump the wires together with a piece of wire or paper clip or similar object and test the furnace to see if it stays running with the switch jumped and then repeat for each one until you isolate which one was causing it to trip. but this will be very time consuming and would be a lot easier to just test them with a meter.
it is up to you if you want to test them one by one as i described or wait until you can get a meter to test them while it is running.
I am a different tech. I have a lot of experience with this unit. There is only switch that will do this...if it were a roll out switch you woud have to press a small reset on the switch itself....you are not doing that so that leaves the main limit.
It is in the top section behind the gas valve...flat against front wall. It is the size of a credit card with 2 wires attached.. Now we have to deciide if the blower runs without shutting down. The HK42FZ was reworked many times because of blower issues.
If the blower actually stops in mid operation...it is a bad circuit board.
If the blower does NOT stop then we have either restricted air flow, too small duct, dirty ac coil, blocked returns etc.
We can also speed the blower up if it is a high temp issue. On the board is a wire from blower motor on terminal HEAT...it is commonly red. We would then remove blue wire from PARK terminal, and put blue on HEAT and red on PARK. This speeds up the blower.
And finally....if all else is done and still faults, you could simply have a bad limit switch.