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I have a York PBKM, model A, computer back up furnace...?
My furnace will fire 85 % of the time with no problem. Once in a while monitoring the unit, found that the ignitor will turn on and the gas valve wont't open then the next thing that will happens is that the blower will start right after on cold mode blowing cold air into the house and at the same time the exhaust blower keeps going too to make matters worse by taking away to heat I already have in the house. Does somebody know what idiot engineer designed this one this way...? The only way to cut this problem is by turning the thermostat off and then re starting with a highest calling temperature, but is a problem when you have to wake up at night few times to do this. I am very sure is not the gas valve because when this happens, I messure no AC 24 volts going into the valve. If you guess, I tried cleaning the heat sensor, also repleced with a new one and then re located at different possitions per previous suggestions to see is this helps. I already know that the sensor is what is trigger the relay on the gas valve to opens while the ignitor is on.I am handy, but this one got me...! Please suggest...! Thanks in advance: Eddie
4 Answers
- gizmoeLv 61 decade agoFavorite Answer
The lock out feature and fan running continuously is a safety feature. Most all manufacturers have also designed in that it restarts the cycle after an hour and some models 3 hours and it will attempt to fire up again.
Also turning off the power and then back on would reset a lock out condition.
Most likely the gas valve relay in the circuit board has pitted or burned contacts allowing it to make a connection on some cycles and not on others. Unfortunately the relay cant be replaced, the circuit board would need to be replaced. This is as long as there are no faulty wiring connections between the circuit board and the gas valve.
The flame sensor only comes into play after the gas valve is energized so it wouldn't be that.
It wouldn't be any safety switches or the igniter would never be energized.
- ObseanLv 51 decade ago
Equipment manufacturers years ago started using timing functions to turn the fan on in the heating mode instead of a thermal switch. It used to be the fan didn't turn on until the heat exchanger got hot. Now the timing is synchronized to bring the fan on when they think the heat exchanger has had time to get hot.
It sounds like the sensor or circuit board may be acting funky.
Sorry I can't give you more info. Their website sucks for technical info. You might be able to Google your furnace and buy the parts online for way cheaper than a contractor will do it for you.
Source(s): 31 years HVAC/Mechanical contracting Maryland State HVAC Master - clcprodigyLv 61 decade ago
Well if you already replaced the sensor seems like you need the computer board, think they are at the source below. Good Luck.
