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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Ducane Model CG95TB080D16C with three blink error. It's been

Customer Question

Ducane Model CG95TB080D16C with three blink error. It's been a very intermittent problem all winter. Resetting power a few times works occasionally. This time, no luck. When power is turned on, the inducer motor turns on and 15 seconds later the HSI starts to glow. The HSI and motor then shut off 5 seconds later, leaving me with a three blink error - pressure swx open with inducer on. I had a service rep out last year for the same problem. He operationally tested the swx, no faults found...and of course the furnace fired right up for him. I checked for incoming voltage to the gas valve: when the power is turned on, it receives 11.8 volts and a few seconds after the HID is glowing, the voltage drops off. Not sure if I have a gas valve issue, or it's not opening due to the pressure switch not closing.
Submitted: 1 year ago.
Category: HVAC
Expert:  Kcrand36 replied 1 year ago.

Hi Ben, I am Kevin....... Can you check the voltage potential across the pressure switch during an attempt for heat?

Customer: replied 1 year ago.
Unfortunately by the time I got to your response, it has started to work it has in the past. Do you have a suggestion of parts I should preventively replace? Second question, do you think this intermittent problem has anything to do with outside air pressure changes...for example, when a low or high front comes rolling in, causing the pressure sensor to react adversely?
Expert:  Kcrand36 replied 1 year ago.

that is a good thought on the pressure sensor Ben, I would agree if the piping "intake and exhaust" was not installed correctly, sized correctly, distances on termination and height and certainly in the same plane, (same side of the house).

I was looking at it more service oriented because you said you had 11.8 volts on the gas valve, when you have a 24V circuit energizing that... Why would that voltage be that low? Maybe because the contacts on the pressure switch or one of the limits are not closing or corroded just enough to create a resistance between the contacts. Hence the thought of checking the voltage potential across the contacts while energized, and hopefully you can do that to the limits as well and verify where we are loosing the power and can then go in that direction for parts or correction.

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