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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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, I have a 1993 Interthermal, model MMHB-056ABHR-06,

Customer Question

Customer: good afternoon.
JA: Thanks. Can you give me any more details about your issue?
Customer: I have a 1993 Interthermal, model MMHB-056ABHR-06, WITH 1018 SERIES IGNITER on it. When you turn up the thermostat it just clicks, does not appear to have ignition, and the red light starts flashing.
I have reste the circuit breaker twice, as well as cycled the on/off switch on the front of the unit.
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Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
still waiting
Expert:  airheatman replied 1 year ago.

Tell me what the pattern of the flash is For example 2 flash pause or three flash pause, etc

Customer: replied 1 year ago.
3 pause
Expert:  airheatman replied 1 year ago.

OK turn high voltage power off to furnace at switch or breaker.THis will reset board.Then back on and call for heat and tell me what happens and if we get same 3 flash code.

Customer: replied 1 year ago.
already did that, twice, both at the circuit breaker and at the power switch, no change
Expert:  airheatman replied 1 year ago.

OK the 3 flash code is an ignition failure issue but we have to find why it failed. Do you have a volt meter to see if we are getting power to the exhaust vent fan?

Customer: replied 1 year ago.
Exhaust fan seems to run, working this problem over the phone, furnace is at my daughters house.
She can hear it making a noise, but nothing happens.
Expert:  airheatman replied 1 year ago.

OK here is the proper sequence we should have.

Thermostat calls for heat the combustion motor starts immediately

Combustion motor pulls a vacuum on the pressure switch closing it

30 seconds later igniter is energized for 15 seconds

Gas valve opens and burner lights

Flame sensor verifies we have flame.If no flame in 6 seconds, burners shut back off

Sequence will try 2 more times.If no flame sensed lockout occurs.

Ask where in that sequence it seems to be failing

Customer: replied 1 year ago.
I had her turn everything back on.
after about the 30 second period she could hear a series of clicking noises, but then nothing happens, then could hear slight noise, believe fan spinning back down
Expert:  airheatman replied 1 year ago.

Our first step is going to be to get a volt meter an check the 120 volts to that inducer fan and see if we get and keep 120v to that motor and verify if it actually comes on and if it stopping with voltage still to it.If fan is stopping and we still have power, the motor could be bad.

Customer: replied 1 year ago.
how do access the power points to the fan?
I will be heading over there this evening.
Expert:  airheatman replied 1 year ago.

I am attaching pic showing where we should be getting 120v to combustion motor.

Customer: replied 1 year ago.
ok, thanks.
Expert:  airheatman replied 1 year ago.

Also here is a link t a manual on the furnace.

Sequence of operation is on page 19

Some troubleshooting steps on page 23

Wiring diagram on page 32

Thanks for letting me work with you.When we are finished, if my answer has been polite, professional,and thorough, please click one of the ratings . If you still need help let me know!.Expert is not paid for assisting you until you rate answer.Feel free to follow up for 30 days at no additional cost. Bonus always appreciated if you feel justified.