Can anyone tell me what year that gas furnaces began using solid circuit
Also a lot of today's circuit boards will allow the blower motor run after
the system shuts down. Can you tell me for how long it will allow the blower
Depends on the brand. 20 to 30 years I'd guess.
Generally somewhere between 30 seconds and a couple minutes. Some are
adjustable. Before circuit boards some still did this but just with a
delayed release relay. You can still buy them.
The very very first boards I saw were on 1974 Day & Night [Bryant] gas
furnaces. They essentially were just so you could plug in the fan relay
[R80128 Honeywell ?]. They had two relays [one for high speed fan - the
other for the Electronic Air Cleaner]. Although there may have been some
The next circuit boards I saw came out in the condensing units by Carrier
around 1974 - 1976 which at that time were called a CPCS [Compressor
Protection Cycle System] which really was not much more than an over current
protection monitor with anti short cycle. [7 minutes normal - 10 minutes on
Then around 1979 or so, the intermittent pilot's starting showing up, and
the boards started to provide timing for the indoor blower on heat. Today
of course the boards are much much more computer oriented with WAN
connection ability, HISTORY logging, and motor speed, gas valve timing
Was that helpful? I provide this only as a free service to other
technicians in the HVAC/R trade.
Yes thank you.
Another technician and I have questioned a control that is sold around here
and I think it is not worth selling but to older furnaces.'
The control allows the blower motor to run after the system shuts down for 3
minutes.The control is mounted under the thermostat and has a LED that tell
the home owner that the control is working
The other tech says that his customers like to see the LED glow and that the
controls runs for the full 3 minutes.
To me with furnaces around 10 years old can do the same but I am not too
sure of a 3 minute run time for the circuit boards.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.