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Heating, Air Conditioning, Fridge, HVAC/Pilot light extinguishes after 20 sec MGV does not open


QUESTION: I have Carrier 58 GS100-3. When thermostat calls for heat the pilot lights up but diminishes in about 20 sec
and MGV does not open. I replaced pilot assembly but problems continue. Is the valve at fault? Bypassing
the pilot gas brings the burners on.

How do you bypass the pilot gas and make the burners come on?
And when the burners do come on how long do they stay on?

---------- FOLLOW-UP ----------

gas valve
gas valve  
QUESTION: I have the schematics for the gas valve. By establishing contact between the green and yellow wires (4 and 5 points) it delivered 24 v to MGV. As long I there is contact the burners come on then ten the blower and so on. Information from Internet

What i'm reading is that the pilot comes on for about 20 seconds but the gas valve dosen't open.
You say you bypass the pilot gas and make the burners come on,
How do you bypass the gas? and what lights the burners?
Sorry but I don't understand?

---------- FOLLOW-UP ----------

QUESTION: Sorry I was not clear.When I connect point 4 to 5 the pilot lights and remain lit , then the main valve opens and burners light up as long 4 and 5 remain connected and bypassing the internal pilot control of the valve
I inserted the schematics with  the previous e-mail

When your furnace calls for heat the first thing that has to happen is the induced draft vent blower comes on, the vent blower blow's the proper amount of air pressure to close the pressure switch, when the pressure switch closes it allows power to the circuit board which allows the pilot igniter to glow, the igniter comes on and sends a message that it's on and ready to light the gas which allows the valve to open, the valve opens and the gas flows and the igniter lights the gas.
If all the stages are working except the gas valve doesn't open it's because the 24 volt power isn't going to the gas valve after the igniter proved it self to be on,  the problem
could be with the igniter, the circuit board, or the power connections, between the igniter and the gas valve.
Your bypass is opening the gas valve and bypassing the safety switch to keep the gas from flowing incase of nothing to light it.

Heating, Air Conditioning, Fridge, HVAC

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Jim Barnhart


Fifty + years conditioning the air.


Answer questions about , residential and commercial. Answer questions about sheet metal fabrication. Fifty years plus experience. No answers for oil equipment, No answers for kitchen appliances, No answers for laundry appliances, I don't specialize in one particular area of the HVAC area, I'm more of a General Practitioner, Limited in refrigeration/

Hands on since 1950

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