York Affinty/4 red flashes/Limit switch????

andymar

I recently purchased a home that came with a York Affinity 9T 2 stage gas furnace. Model #PT9C20N100DH11A, installed in 2006. I have recently noticed an issue as we just had a cold snap here in northeast (zero degrees). The unit fires up and runs fine for exactly 45 minutes, then shuts off. This occurs even though there is still a call for heat. After 60 minutes the unit starts up and, runs for 45 minutes , then shuts off, and so on. It also appears the cycle is not going into the higher heat/stronger blowing, mode. The unit is flashing 4 red lights. Manual says poss. cause : dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate or faulty blower motor. I replaced the dirty filter and the ducts haven't changed. Back of door states, Fault code, 4 Red, limit switch open. My question is are these symptoms connected to a bad high limit switch, which I believe is mounted on the heat exchanger (not on inducer motor? Switch I am describing is about three inches long going into the unit. The run time of exactly 45 minutes has me perplexed. Can I try to jump the switch in question?

DZoro

Do NOT jumper the switch. The dirty filter caused the limit to trip. Now that you have a clean filter make sure all the supply and return registers are clean and fully opened. Nothing should be blocking any of them.
May need a tech brought in for further evaluation and cleaning.
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andymar

Thank you @DZoro I value your expertise as you helped me two months ago with another issue. I thought I could jump that switch to see if it cleared the flashing red light. If all issues pertaining to air circulation are corrected, will the code clear itself. Also the 45 minute to the T run time has me perplexed.

DZoro

That's a fairly large furnace. How large is your ductwork, how many returns, supply's?
When the burners go into second stage (hi fire) do you notice a change in main blower sound/speed? In order to do this turn the thermostat down until the furnace shuts down. Then turn the thermostat 1* above room temp, (1st stage) then have someone turn it 3* or more above room temp. Shortly thereafter the furnace should go to high fire, depending on if you have a single stage stat or 2stage stat.
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DZoro

The 45 minute run time with a fresh filter is telling me your ductwork is inadequate. It is unable to remove all the heat it is producing in high fire. Thus limit is doing its job!
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andymar

Thank you @DZoro. You are a genius. Knowledgeable to say the least. I opened one supply vent on the first floor and one on the second floor, now all opened. The unit is running fine. Green light flashing. The unit will stay on for longer than the 45 minutes if needed. The unit does kick in to a second stage upon increasing the therm. temp. Along with the changes I believe I made the mistake, the other night, of lowering the overnight temp to 50*. This original part of the home is very poorly insulated, a wooden kit house built in the 30's, kinda like the Sears houses sold back then. The overnight outside temps plummeted into the zero *s and unit had a hard time getting the ambient temp. up. First floor of 750 Sq. ft. has a 13 by 24 inch return with six 9 inch supplies. The second floor, where unit is located is approx. 350 sq. ft. with a 13 by 14 return and four 8 by 12 supplies. I was trying to temper down the heat upstairs as it does get hot up there along with keeping a laundry room on the floor cooler, hence closing them. Thermostat is centrally located on the first floor. Thank you very much for your help.
PS- Regarding the new Weil Mclain combi unit you helped me with several months ago, I apologize in not getting back to you. I failed to get the settings from the technician that calibrated the unit.

DZoro

Thanks for the compliment and mostly the feed back. It is nice to hear back from the home owners when things are actually solved, and what exactly solved them.
Yes the set back was too much, might be able to get by with that in the lite heating season, but not now.
The same goes with turning down the duct dampers.
That furnace is extremely oversized for your house, I'm actually surprised it even goes to second stage. When it does you will need clean filters and clear open ducts.
No deep setbacks, try to keep that furnace in first stage.
Constant fan on will help distribute air and help some with hot and cold spots. Just need to change the filter more often.
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Dave0176

This is an overheat protection usually caused by undersized duct work and an oversized furnace. 4 blinks on a York is limit switch tripped. I see it all the time. The heat can’t get out, there’s no place for it to go.