how to test intermittent gas valve?

[jgy2001]

I have a Trane gas furnace with a air-conditioning combination unit.
The Trane gas furnace model is TDD140R960C5 around 8 years old. The furnace Controller is White Roger Emerson, Model 50A51-495. Yesterday, the furnace stopped working. I tested the furnace. I found after the thermostat turned on the furnace, the controller clicked a sequences and the glow igniter device turned on three times. The small blower at the exhaust turned on. However, the gas valve was not turned on. At the end of the sequence the blower turn on, but was blowing un-heated air. I noticed the controller LED did not blink any special sequence, just normal slow flashing. I test my gas water heater, sitting next to the furnace and the heater worked fine. Today, the furnace is working again.

I suggest suspect the valve is intermittent. Can you please tell me, according to my picture:
What kind of gas valve I have? I assume this is the unit labeled “R”. How to test if this valve is faulty, online?
What is the function of this small fan at the exhaust?
What is this two round metal cans, labeled “P02 Low” and P01 HI”?

thank you.

[HayZee518]

valves

R is your main gas valve, the two "p"s are pressure switches. the one labeled low would be open and the high would be closed. it looks like they're part of the burner's safety system. you need to look at your system schematic to see what conditions apply for your burner valve to open. we can just guess what's supposed to happen at this point.

[jgy2001]

attached please see the schematic

[HayZee518]

small blower in exhaust

that blower is also called the induced draft fan. it imparts a negative pressure so that the burners will ignite. I'm looking into the main gas valve from several sources.

[HayZee518]

parts

try this:
hvacpartsoutlet dot com.
I found a goodman valve
Goodman Janitrol Amana Factory Replacement Part

2 Stage Gas Valve
Part Number B1282617

White Rodgers 36E54 Type 238

[jgy2001]

Thank you.
I can see the Goodman gas valve White Roger 36E54,
but how do you know its type 238?
In the photo, you can see the part number 36E54, but have 201 after the part number?

[HayZee518]

valve

why don't you call the phone number of the owner of the site?

[jgy2001]

well, the furnace stopped again. The White Rogers Model 50A51-495 controller LED is flashing 2 times = system lockout / no flame / check line polarity. What does check line polarity means?

I turn the power off. Then, knock the Gas valve couples times with a screw driver. Turn the system power on. The furnace is now running again.

Is there anyway to test and oil this gas valve?
Looking at the valve picture, what is the exact manufacturer and model number?

[HayZee518]

gas valve

you NEVER oil a gas valve! it is made to exact specifications to operate sufficiently. if there is a problem, which in your case there is, replace the whole valve. maybe something inside wore down or got misaligned. Gas valves are not user friendly. I would suggest at this stage to hire a plumber, gas certified to check/replace your valve. I will NOT accept any liability if you make a mistake.