Heating, Air Conditioning, Fridge, HVAC/Concorde 80 plus Draft Inducer
QUESTION: My Concorde 80 furnace is about 11 years old. About 3 years ago the furnace stopped coming on automatically, and I have been able to get it to come on manually. It shuts off in the normal way when the temperature reaches the thermostat setting. From my understanding, the draft inducer is supposed to start when the temperature drops below the setting on the thermostat. This allows the pressure switch to close so the furnace can ignite. What I have experienced is that the draft inducer does not start and my system error light blinks twice, with an error that the pressure switch is open when it should be closed. This makes sense. However, if I vary the connection at the pressure switch the system will turn the inducer on and then operate normally. I put a meter on the system today, and there is no voltage coming to the motor during the initial request, but there is voltage at the motor when I vary the connection at the pressure switch. So, why would there not be power during the first part? What can I do to find the problem? Thank you for the help.
Once your t-stat calls for heat, providing all your safety limit switches are closed ,the next step would be for the Inducer motor to come on, once it reaches the correct RPM it suppose to close the normally open pressure switch. You state " an error that the pressure switch is open when it should be closed. This makes sense. " look at the wiring diagram ,it should show the pressure switch is normally open not closed.If you do not have 120 Volt ( assuming your unit is 120 Volt AC ) at the inducer motor ,your board may be bad. Need to follow the wiring diagram to see where the two motor wires hook up and check there. You can bypass the t-stat and jumper the low voltage terminal strip where the t-stat wires go ( you may have make sure the blower motor door switch is closed as there usually is a switch on it ) Jumper R to W to start the heat,
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QUESTION: Okay, so you say that once the t-stat calls for heat, the next step would be for the inducer motor to come on. In my furnace, there is no voltage to the motor at this point. The 2 motor wires go to a wiring harness with 2 other wires that connect into a control module of some kind.
Do you have any idea why the system will come on if the pressure switch opens and closes in a rapid sequence, but won't come on initially? It would appear that all of the other safety switches are okay because the system operates normally otherwise. Thank you for your help.
You can try to bypass the wiring harness ( you state the two motor leads go to a harness then coming out of the harness it goes to the a control module. ) possible there is a bad connection there. keep working back to see where you lose voltage .Reference the wiring diagram. That's how we troubleshoot. You may have a bad connection or a bad board. I assume when you say " the system will come on if the pressure switch opens and closes in a rapid sequence " that you are physically moving the part. I do not know why the motor would start when you move the pressure switch without actually being there. Also double check all your wiring hookups are correctly hooked ,such as your limits any relays, you do state " About 3 years ago the furnace stopped coming on automatically, and I have been able to get it to come on manually." so guessing you made modifications. Need to go back to original wiring per diagram, then check if you have voltage at motor. You sound very electrically/mechanically inclined. Buying parts online would still save you a lot of money vs calling for service and their mark up on parts.
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QUESTION: Hi, thank you for your help. I think I understand a little more and have done some additional checks. So, when the t-stat calls for heat, the draft motor does not come on and the error I get is that the pressure switch is closed when it should be open. I disconnected one of the wires to the pressure switch and reset the system and I get the same results: no draft motor and an error that says the pressure switch is closed when it should be open(although the environment I created is an open switch environment.) I put a meter on the draft motor, and there is no voltage when the t-stat calls for heat. I put an ohm meter on the pressure switch and it is open in the normal environment. The draft motor will come on and the furnace will cycle off normally if I vary the pressure switch connection open/close a few times. Do you have any additional thoughts on why this might occur?
I briefly looked up a wiring diagram for a typical Concord 80% shows the inducer motor hooks to a control board, black and white wire goes to terminal 1 and 3. the 120 volt feeding the board goes to L1 and neutral. You need to verify that you have constant 120 volt feeding the board. The pressure switch is not interlocked with the inducer motor, meaning it has nothing to do with it. The wiring diagram shows the pressure switch is 24 volts circuit from pin 1 to pin 10 ,which is normally open ,the other safety controls in series with the pressure switch are normally closed. So if you bypass your t-stat and jumper R to W to G at the furnace and the inducer motor does not start you may have a bad board. Personally you sound like a electrically/mechanically inclined person, I would buy a new board via internet HVAC parts. install and see what happens. Need to verify none of your limits open. Other than that I do not know what else to tell you. your words,.. "So, when the t-stat calls for heat, the draft motor does not come on and the error I get is that the pressure switch is closed when it should be open." Troubleshooting via internet is difficult, but for a start I would replace the board, verify all your limits are closed and the wiring is correct to the wiring diagram.