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Old 12-21-2005, 05:33 PM   #1
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Magic Chef oven won't light, revisited

I need to readdress the many oven wonít light threads.

I have a 1964 Magic Chef LP gas, four burner stove with oven. The stove works as advertised. The oven burner wonít light. It has a Harper-Wyman 5850 safety valve with a 14" sensing element.

I removed and cleaned the oven parts and replumbed all gas lines. Opened the main oven gas valve, did leak checks and lit and adjusted the constant pilot which works fine.

I set the thermostat control knob to 300. The secondary heater pilot immediately lights and I adjusted it to heat the sensing element probe. I then wait 2-4 minutes. The burner does not light, no smell or sound of gas from safety valve to burner orifice.

I then disassembled a second safety valve out of a parts oven and verified the valve spring unit moves when the sensing element probe is heated (valve appears to open), then reassembled it.
I installed that safety valve unit and still nothing happens.

So:
The safety valve has gas to it supplying the constant pilot.
The thermostat control knob sends gas to the secondary heater pilot on demand.
The sensing element probe to the safety valve heats up to red hot.

Questions:
How do I test the oven safety valve in or out of the oven and confirm it is good or faulty?
How can I rebuild a faulty safety valve myself?
Does anyone know a specific source for replacements for Harper-Wyman 5850 oven safety valve?

Next:
How do I test the oven thermostat if and when I get the burner to light?

I have Santa cookies to bake and need help
Thank you, Safari64
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Old 12-21-2005, 08:18 PM   #2
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You are sure your thermocouple is working and the electromagnet is functioning and not getting hung up in it’s assembly, and you have the proper regulated gas flow, it should work. Try shorting out the thermostat to by pass the hydraulic bulb as the problem. The range should light. I have taken my assembly apart and heated the thermocouple and watched the electromagnet snap on. (surprising amount of magnetic pull). It sounds like you have done something like this, which eliminates the thermocouple electromagnet. Short the thermostat out. There is really nothing left that I can think of off hand except take the whole assembly out of the stove and do a bench test hooked up to a regulated gas line. You don’t need the thermostat just bypass it for testing. Make sure all the rubber gaskets and seals are not sticking. You can repair it yourself. Try your local appliance parts store they may have something that is universal for your project. Keep us posted…..
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Old 12-21-2005, 08:25 PM   #3
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To test the temperature of the oven when you get it working try one of the Infared non-contact thermometers. Target the back of the oven for temperature, a leaking door seal will give you a higher reading toward the front of the oven where they leak out heat. Or just a cheapo oven thermometer. You can pick one up at Wally World next time you overnight in their parking lot.
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Old 12-22-2005, 03:07 PM   #4
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Thanks for the help.

Let me make sure I have my oven parts right:
The thermocouple is the sensing element probe leading to the electromagnet inside the safety valve and the thermostat is the probe with the hydraulic bulb from the main oven control knob unit. When heated thermostat should cut off flow of gas to secondary pilot, shutting off safety valve.

When I had the safety valve out on the bench opened up I used a torch to heat the thermocouple. The electromagnet (with spring and brass arm) moved inward slowly but there was no magnet type snapping open, no 30+ second delay and Iím not sure if it opened the valve fully. I can bench test it hooked it up to regulated ľĒ LP gas line from the BBQ like fish fryer tank, will that work? Sounds like a fire waiting to happen if the valve opens without burner installed and Iím standing there with a torch.

How can I short out / bypass the thermostat?

Alaska is the ONLY place Iíve been where Wally World parking lot has ďNo Overnight CampingĒ posted.

Thanks, Safari64
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Old 12-23-2005, 05:30 PM   #5
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First off, do not over heat the thermocouple it can ruin it. Thermocouples should just be next to the flame (very Close flame edge licking it) but not in it. That will produce enough current to cause the magnet to snap home (over coming the spring tension) to open the valve. The safety valve acts quickly. They do not to take their time opening and closing because they are intended to CUT THE GAS OFF NOW!!!! preventing a very serious gas leak.
The thermostat is either open or closed. Just disconnect the thermostat wires and use a jumper wire to simulate the contacts. As the oven hydraulic bulb heats, the fluid inside the bulb expands which terminates at a small bellows that expands and contracts with temperature. That in turn pushes a switch that opens the gas valve or closes it. So you can see that you don’t need the hydraulic valve just a jumper wire with a roach alligator clip on each end. You can use compressed air into your regulator instead of propane as a gas source for safety. If you do not have access to a flow gauge put a balloon over the end of the burner pipe to see it if the valve is working. The balloon will not blow up but will indicate if there is gas flow by puffing up.
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Old 12-23-2005, 05:52 PM   #6
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Safari64
I was a little confused about the second pilot light. Generally if the second pilot light is in the oven you are required to light the oven pilot light every time you intend to use the oven with the oven knob turned ON. This pilot is supposed to stay lit while the oven knob is ON or set to a temperature like 300 degrees or whatever temperature you need. When the oven pilot heats the oven thermocouple, that will allow the main oven gas valve to open and flame the burner. When you turn the oven knob to OFF that cuts the gas to the oven pilot light, which cools the thermocouple preventing gas to flow to the burner. This lighting the oven pilot every time you want to use it is a safety feature so the pilot light won’t blow out while blazing down the alcan highway allowing gas to fill the trailer. Remember the oven pilot must be lit every time you intend to use the oven. Hope I have been some help.
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Old 12-23-2005, 06:06 PM   #7
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I have the same oven, and there is a "pilot only" setting on the knob, so if you are planning on doing further baking, you don't need to re-light the whole thing.
Also, it takes at least a couple of minutes before the main burner lights when you turn the knob to an "on" setting. I do have a problem with mine, after the main burner kicks off when it reaches the set temp, it blows out the pilot as well. A minor issue.
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Old 12-23-2005, 06:56 PM   #8
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Thanks, These have been very helpful.
Perhaps Iíve confused things a bit. My stove/oven is a 1964 Magic Chef Model T720. It has two pilots.

To use either stove or oven you open main gas valve under cooktop lid and light stove pilot. Stove burners light fine. When you want to use the oven you open the oven gas valve on the manifold. This valve is independent of the main stove gas valve and is input to safety valve and primary pilot. Then open oven door and light the primary-stationary pilot.

Turning the oven control knob to call for heat then sends gas to the secondary pilot which is lit by the primary-stationary pilot and then heats up the thermocouple, opening the safety valve, and lights the oven burner. When thermostat is satisfied the hydraulic bulb shuts the gas flow from oven control, extinguishing the secondary pilot, cooling thermocouple, shutting safety valve. Turning knob to off does the same. Thatís what Terry is saying, his blows out the primary pilot when burner shuts off. We'll figure that one out too.

So, with these units after traveling you have to turn on stove gas, turn on oven gas and relight the oven stationary pilot.

Testing with compressed air is a good idea, Iíll try that.

My thermocouple is mounted directly above the secondary pilot. Perhaps it does get Too hot. Should it be off to the side? I adjusted secondary pilot flame down to where orange tip dissappears leaving just blue flame.

You lost me with ďdisconnect the thermostat wiresĒ. My unit has NO wires visible. The thermostat bulb is at one end and other end screws into the control unit (looks like a thermocouple connection on a heater). I havenít tried removing it, donít need to yet. You are correct I donít need the thermostat Yet, until I get the burner to light.

On a website for Old Appliance Club (I collect old toasters, go figure) I found a guy that will test safety valves and thermostats for antique household ovens. Perhaps I should just box them up and have them tested properly.

Thanks for the help, weíll get them going yet,
Santa wants his cookies
Safari64
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Old 12-23-2005, 07:14 PM   #9
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Mine has no wires, either. All electrical generation is strictly internal, so no wires.
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