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Robert, HVACR Educator
Category: HVAC
Satisfied Customers: 161
Experience:  Licensed Mechanical Contractor, 30 years experience, 20 years teaching experience
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I have a White-Rodgers model 50A50-406 control on my furnace.

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I have a White-Rodgers model 50A50-406 control on my furnace. Yesterday evening there was a short in a upstairs electrical socket, and the circuit breaker tripped. I reset the circuit breaker but the furnace will not come on now. I check to see if there was a reset switch but cannot find one. Also on the diagnostics it says that if no flashing led then there is no power. Could the shorted electrical socket have thrown it into lock out? If so how do I reset it.
Hi, I'm Bob .

When you are back online let me know.
Customer: replied 7 years ago.
Hey Bob, I am online
Hi there. You mention an electrical short. Did this occur in a different area than the furnace?
Customer: replied 7 years ago.

Yes, an electrical outlet shorted when a lamp was plugged into it. It blew the breaker. I had no idea it was tied into the furnace line


Ok, I have to believe the lamp circuit is separate from the furnace. Go back to the breaker box and look for a breaker labeled "furnace" Is there one labeled that way?
Customer: replied 7 years ago.
Yes, I already checked that breaker and went ahead and flipped it off and back on again just to be sure. Still have no control Led on the control box.
Make sure the panels are securely installed (there is a safety switch that needs to be closed) Look for a switch near the furnace on the outside, make sure it is on. There may be a fuse in a little box on the switch.

Side question: does the lamp circuit work now that you reset the breaker?
Customer: replied 7 years ago.

yes the electrical socket works after resetting the circuit breaker.


I looked on the outside switch of the furnace for a fuse but there is no opening into the switch box. It is a regular metal electrical box with a on/off switch, no room for a fuse. and it is turned to on position.

Ok, I believe the electrical problem you had and the furnace problem is coincidental unless there is a major issue with your breaker box. How do you feel about checking voltage? do you have a volt meter that works?
Customer: replied 7 years ago.
I do have a working voltage meter and have no problems checking voltages.
Good. First of all, remove the switch at the side of the furnace and check power there. You can simply check between one of the connection screws and the box. If you have no voltage you will have to go back to the breaker box and remove the cover and check the breaker. If you have power at the switch then we'll have to get into the furnace. I'll get back to you shortly. I have to head off to teach a class. I'll have my laptop there.
Customer: replied 7 years ago.
okay.. I finally was able to get the switch cover off to get at the wires.. was not in a very easily accesible location.. I have voltage there... so where next do I check?
Ok, take off the furnace doors and go to the main board. You will find the incoming power is connected. The terminals should be labeled L1 and L2. Tell me the make of your furnace also.

Customer: replied 7 years ago.

the furnace is a Trane XE90 propane converted to natural gas.


I did not find any L1 or L2 located anywhere on the controls. but, when I checked the safety switch it has 120vac when it is pushed in.

There is a small automotive fuse on that board. You will have to look around for it. I have to run to my mothers house to fix her furnace (she's 83) I'll be back.
Customer: replied 7 years ago.
okay.. I removed the wires from the box and opened the circuit board assembly. I found no fuse on the board. It is a very old style pc bd and doesn't even have a coating applied to it. it is an offwhite in color. and single layer component mounting. I am going to reassemble the control box and keep looking for this fuse. talk to you after while.
We need to find out if there is 120 volts applied to the board first. If there is then we need to determine if there is 24 volts on the control side. If the light is not lit I doubt there is 24 volts on the control side. If there is 120 volts to the board and no voltage between R and C terminals on the terminal strip then you either need a board or the fuse is bad. These fuses are automotive type flat plastic 3 amp fuse.
Customer: replied 7 years ago.
which wires would I pick up the 24 volt supply?
Between R and C on the terminal strip where the thermostat wires connect.
Customer: replied 7 years ago.
okay.. will check this and be back in a bit.
Are you doing OK?
I Hope everything is OK.
Customer: replied 7 years ago.

Hello Robert, I still haven't located the fuse. I will keep searching today. I have a weak internet connection and lost it completely last night. I did find that there is voltage into the transformer but none out. A schematic of the pc bd would be nice, especially since I have no idea about auto fuses and what they look like. The fuses in my car are a 2 prong plug in and color coded for different amperages. My experience with electronics is welding equipment repairs. Okay, I will let you know when I find the fuse and if it is good or not.

by the way! I appreciate you walking me through this. I lost my job in September and really cannot afford a HVAC repair tech right now.

That is the type of fuse that is on the board. If you have power into the transformer and nothing out the tranformer is bad. Please double check that.
Customer: replied 7 years ago.
okay it is the transformer, there is 120.2vac in and nothing out. Any idea where I can find a replacement. I found its a Products Unlimited Corp step down probably part# XXXXX
Your best bet is your local Trane dealer.
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