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I waited until September this year to have what I thought was a higher level technician come out and try to troubleshoot the problem with my furnace (model 39AAZ***. You may remember me from last heating season). The technician thought he noticed the output from the 24V transformer sag a bit, and he concluded this was the problem, so I declined having him replace it (for $174) and instead ordered one myself on the Internet (for less than $40), got it and installed it, and with light usage and few cycles it appeared to be okay, until one weekend in early November, same thing happened as has been happening since 2003:
The thermostat calls for heat, the inducer draft motor starts up, and within one minute it stops, before the main burners come on, and before anything close to the 5-minute lockout timer elapses. I don't know if the pilot is on when the inducer motor stops. There's just no technology around that I have that could help me determine that. I just have to cycle power (either with the master power switch at the furnace, or simply at the thermostat) to get it to come on again, and most times it just starts up and continues as it should.
It has gone up to three weeks without a hitch, and other times as little as a few hours between cycles, before failing. Currently it seems to be averaging about three days between failures.
All electrical/electronic parts have been replaced, except for the gas valve itself (containing the pilot hold switch and other relays for the gas functions), and this includes:
- the ignitor lockout module
- the inducer draft relay circuit board
- the pressure switch
- the inducer draft motor assembly
- the blower relay circuit board
The venting has been checked and examined for obstructions. I most recently (at the suggestion of the latest technician to visit) disconnected the inducer vent intake for a few days to see if there might be problems with pipe diameter, length, or excess bends. It ran fine, but failed in around three days.
No apparent backup of drain water, either.
Yessiree, it's got everyone stumped. Keep in mind, this unit is pre-microprocessor. It always re-sets successfully, immediately after a failure.
The biggest mystery is whether the pilot makes it on before the failure, and the biggest clue is that it shuts off within a minute (usually much less).
I'm a repair technician for another type of machine, and I believe in things being fixable. I don't see any reason for something like this to be replaced (especially considering the cost), except that the available brainpower and experience in evaluating such a problem seems to be at an end, and one can only guess what the guys at the Bryant factory could come up with, if they could be brought into this (the whole HVAC industry seems very closed-shop, non-DIY oriented, dealers need to know only).
So if any of you have anything further to suggest, feel free. But keep in mind all of the things I've laid out here. I have a .pdf file of the "Sequence of Operation" and schematic diagram from the owner's manual, and if I can find a way to post it here, I will, otherwise, e-mail me and I'll forward it to anyone who'd like to take a look. (Just tried, and my .pdf is too large, so if interested, send me a msg.)
If anyone is good at DIY electronics, I'd really like to hear about designing and building either a device to automatically reset the furnace (cycle power off/on), or at least monitor any and all functions that contribute to lock-out conditions (sequence and timing of control signals, etc.)
Thanks for reading.
The thermostat calls for heat, the inducer draft motor starts up, and within one minute it stops, before the main burners come on, and before anything close to the 5-minute lockout timer elapses. I don't know if the pilot is on when the inducer motor stops. There's just no technology around that I have that could help me determine that. I just have to cycle power (either with the master power switch at the furnace, or simply at the thermostat) to get it to come on again, and most times it just starts up and continues as it should.
It has gone up to three weeks without a hitch, and other times as little as a few hours between cycles, before failing. Currently it seems to be averaging about three days between failures.
All electrical/electronic parts have been replaced, except for the gas valve itself (containing the pilot hold switch and other relays for the gas functions), and this includes:
- the ignitor lockout module
- the inducer draft relay circuit board
- the pressure switch
- the inducer draft motor assembly
- the blower relay circuit board
The venting has been checked and examined for obstructions. I most recently (at the suggestion of the latest technician to visit) disconnected the inducer vent intake for a few days to see if there might be problems with pipe diameter, length, or excess bends. It ran fine, but failed in around three days.
No apparent backup of drain water, either.
Yessiree, it's got everyone stumped. Keep in mind, this unit is pre-microprocessor. It always re-sets successfully, immediately after a failure.
The biggest mystery is whether the pilot makes it on before the failure, and the biggest clue is that it shuts off within a minute (usually much less).
I'm a repair technician for another type of machine, and I believe in things being fixable. I don't see any reason for something like this to be replaced (especially considering the cost), except that the available brainpower and experience in evaluating such a problem seems to be at an end, and one can only guess what the guys at the Bryant factory could come up with, if they could be brought into this (the whole HVAC industry seems very closed-shop, non-DIY oriented, dealers need to know only).
So if any of you have anything further to suggest, feel free. But keep in mind all of the things I've laid out here. I have a .pdf file of the "Sequence of Operation" and schematic diagram from the owner's manual, and if I can find a way to post it here, I will, otherwise, e-mail me and I'll forward it to anyone who'd like to take a look. (Just tried, and my .pdf is too large, so if interested, send me a msg.)
If anyone is good at DIY electronics, I'd really like to hear about designing and building either a device to automatically reset the furnace (cycle power off/on), or at least monitor any and all functions that contribute to lock-out conditions (sequence and timing of control signals, etc.)
Thanks for reading.
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