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mranswer, HVAC Mechanic
Category: HVAC
Satisfied Customers: 6160
Experience:  20 years experience running my own business
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I have a AIRQUEST natural gas furnace that is about 20 years

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I have a AIRQUEST natural gas furnace that is about 20 years old model #NNCU075AG01. The blower would come on when the thermostat called for heat but only cold air came out. When I turned the thermostat down it would shut off the furnace/blower. I removed the cover on the combustion chamber where the front of the burners and pilot/ignitor are. I found the ground wire broken off from the attachment point on the ignitor/sensor base. So, I replaced the connector on the wire and reattached it. No spark or pilot would light when I fixed the ground wire and turned the thermostat to call for heat. I replaced the igniter/sensor even though a continuity test with a multimeter of the old igniter said it was "OK". Now the sequence that occurs is the thermostat calls for heat , the exhaust gas blower starts then the ignitor sparks and the pilot lights quickly every time. The main gas valve solenoid is heard to click and the main burners come on for about 3 seconds and then shut down. This sequence happens over and over again. I can hear the main gas valve solenoid clicking each time the main burners light and then shut down. The funace has a White/Rogers gas valve Model 36E38214 that has a main solenoid and a second redundant solenoid. My question is: Is it the gas valve or the control module that needs replaced?
Get a voltmeter and see if power is present at the valve coils when the flame goes out- if it is then the valve is bad; if not then the control is as it must not be sensing the presence of the pilot flame. Make sure the flame sensor is in the flame otherwise it will drop out.
Customer: replied 4 years ago.

It is 24Volt AC at the gas valve, Right? And can I just touch the spade tipped electrical contact on the gas valve marked MV with the red lead of my mutimeter and the ground lead of my mutimeter to the frame of the furnace?

This is not a car- there are no measurements made to ground because wires are used to conduct, not the furnace frame. MV stands for main valve, so measure between MV and the common wire on the valve and you should read close to 24V. PV is pilot valve, and it should be marked as well, so that may help you identify the common wire.
Customer: replied 4 years ago.

I placed the red probe of my mutimeter on the MV connector on the gas valve body and each time the burners would light I heard the solenoid click and the meter read about 24 volts. The black lead of the mutimeter on a screw on the furnace frame did provide good ground. Also, I did try to adjust the sharpness of the pilot flame with the adjustment screw on the gas valve but I saw no change no matter if the screw was all the way in or out. I adjusted it with the MV lead off and the thermostat calling for heat per the instructions that came with the Honeywell replacement ignitor/sensor. I have adjusted the tip of the ignitor/sensor per the instructions that came with the part. Thanks, XXXXX XXXXX it must be the gas valve.

Volts to the main valve coil and no flame means bad valve as I said.
Customer: replied 4 years ago.

I only see a 24 volt reading when the solenoid clicks "on" then it goes to zero and the burners go out so is it the valve or the control? There is no power when the burners are out and I here the solenoid actuating.

That is the control- a valve should be working when it has power just like a light bulb should lite when it has power. I explained this earlier as well.
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