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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8048
Experience:  Furnace, A/C and heat pump specialist.
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I am trying to troubleshoot a sudden problem with my York

Customer Question

Hello, I am trying to troubleshoot a sudden problem with my York furnace. Furnace has been inactive for a couple weeks as we are moving from cooling to heating season. A/C was working fine a few weeks ago and I went to bump the heat the other morning when it got chilly and I am getting no response from the furnace at all. Thermostat seems to be calling for heat/cooling as required but I cant even get the blower fan to come on manually. Don't seem to be getting 24v power back to the thermostat. How can I tell if the transformer is possibly bad?
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Troubleshooting often requires meters and test equipment.Do you have a multi meter for testing voltage? If not you can get an inexpensive one at Walmart for about 15 bucks, if you have or would like to obtain a meter to troubleshoot , I will be happy to guide you.Without a meter , there are a limited number of things we can check if you are able to do a visual inspection and can do some hands on troubleshooting.Please let me know and we can go from here

Customer: replied 1 year ago.
I do not have a multi meter but could obtain one. I do have a voltage tester that just simply detects the presence of voltage. There are four wires on the transformer (which is 120v/24v). There are two larger wires coming from the control board terminals marked XMR which I presume are the 120v side and two smaller wires that lead to a wire harness back on the control board which I presume to be the 24v. Assuming that the voltage tester detects down to 24v, I tested the red wire on my thermostat and I get nothing. I tested the 4 wires on the transformer and the tester indicates voltage on the two larger wires but only on one of the smaller wires (the blue one but not the black one).
Expert:  airheatman replied 1 year ago.

Those little light testers usually will not light up with 24v.. Lets do this.

Take a jumper of some kind and jump R to W )(thermostat wire connections)on furnace control board and see if heat will come on and R to G and see if fan will come on.

http://i.imgur.com/JprQdYv.png

Customer: replied 1 year ago.
I am at work now and don't have access to the furnace. I did try already to jump the R and G wires to bump the fan but I did it at the thermostat, not the control board. Would it make a difference?
Expert:  airheatman replied 1 year ago.

Should be the same unless we have a break in control wire between tstat and furnace.Depending n model of furnace you may have a small 3 or 5 amp fuse on control board that could be blown.If you can grab a meter on the way home we can troubleshoot.Keep I mind though that if fuse on board is blown or thermostat is burned up, there could be a short somewhere that caused it to pop.Simply replacing fuse or transformer may result in burning new one.Short will need to be found and eliminated.Shorts can be difficult to find unless a wire is bare and touching such as being chewed by an animal or hit by a weed eater .I recommend once we find if it is fuse or transformer that we get several fuses for troubleshooting.

Customer: replied 1 year ago.
I could not find any fuses inside the furnace itself on or near the control board. Is that common? Would there be a fuse inside the transformer itself?
Expert:  airheatman replied 1 year ago.

Older furnaces did have the fuse on the board .It is a good possibility transformer is bad if we have voltage to transformer, but nothing will come on. I recommend we put a fuse in one of the low voltage wires when we replace it just in case there is a short. Get a pack of 3 or 5 amp car fuses .See below:

http://i.imgur.com/Aqd9O0f.png

Customer: replied 1 year ago.
Roger that. Should we do some more troubleshooting before I actually buy a transformer? Where could I buy a transformer if that is what is needed?
Expert:  airheatman replied 1 year ago.

I like to troubleshoot and verify .If you can grab a meter,that would be best.AS for transformer and the fuses, you can get at any appliance parts store that sells washer,drier and refrigeration parts.A standard 40VA 120/24v transformer should be less than 20 bucks and a box of fuses as shown about 5 bucks.

Customer: replied 1 year ago.
Will do. How late will you be available for live chat this evening?
Expert:  airheatman replied 1 year ago.

I am usually in office until 9 or 10

Customer: replied 1 year ago.
Thanks. I will ping you later.
Expert:  airheatman replied 1 year ago.

Sounds good.Look forward to working with you

Customer: replied 1 year ago.
okay Airheatman, I am back with multi-meter in hand. Are you available to continue our chat?
Expert:  airheatman replied 1 year ago.

Sure,Look in burner compartment and get me model off of label so I know exactly what we are working with.

Customer: replied 1 year ago.
York model P3URD12N07501A
Customer: replied 1 year ago.
FYI, I also have owners manual and wiring diagrams if that helps.
Expert:  airheatman replied 1 year ago.

OK set meter to check AC volts 200. Then check for 120 in between white and brown and for 24v out between black and blue.

Customer: replied 1 year ago.
120v confirmed on white & brown. reading 0 on black and blue
Expert:  airheatman replied 1 year ago.

Ok transformer is definitely burned up then. I would put a fuse in one of the low voltage wires when replacing. Also look good for any chewed or cut marks on control wire between furnace and thermostat and outdoor unit and furnace.

Customer: replied 1 year ago.
I did check the wires out to the A/C unit before dark and all looks/feels good. I also don't see anything on the wires inside furnace or on the thermostat wire that I can get to. What else would cause a transformer to go bad?
Expert:  airheatman replied 1 year ago.

Power surge, wires touching somewhere, wires connected wrong at thermostat, or a shorted component such as contactor,thermostat or fan relay.

Customer: replied 1 year ago.
okay. I will try to find a transformer tomorrow and replace. I did get some fuses and an inline fuse holder today so I will put that on as well. I assume that if there is a different problem somewhere else after that, the fuse will blow before the transformer burns out?
Expert:  airheatman replied 1 year ago.

That is correct fuses are much cheaper than transformer is why I like to have the fuse inline.

Customer: replied 1 year ago.
If for some reason the transformer does not work or the fuses continue to blow, can we still pick up this chat tomorrow and continue?
Expert:  airheatman replied 1 year ago.

Absolutely

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