I have a Lennox furnace (G26) with a problem now: the blower fan cannot be auto on or off, I should always put it to ON from the controller. If I put it to Auto, it wouldn't work.
Please help me figure out the problem.
On Monday, March 9, 2015 at 1:53:10 PM UTC-4, email@example.com wrote:
What happens when it's on auto? Furnace fires up, overheats, then shuts down?
What age is this furnace? If it's an old furnace, they used a thermostatic
switch that turns on the blower when the plenum gets warm enough. Newer furnaces for probably last two decades typically have the on/off function
designed into the main control board. If you have the former type, then
it's probably the thermostatic switch. If you have the latter, it's a bit
strange, because the controller board also has to turn it on in response to
the thermostat fan switch calling for it to be turned on when you do it
manually. So, it would seem more likely that the fan just wouldn't go on
at all, but it's possible a fault on the controller board could cause it.
When turning it on Auto, the furnace can fire up, but the blower fan will never on. This causes furnace to be overheats then shuts down.
The furnace is about 8 years old.. where is the thermostatic switch located most likely?
On Monday, March 9, 2015 at 2:53:17 PM UTC-4, Patrick Feng wrote:
With the model number you should be able to find a wiring diagram online.
Or there typically is one on the inside of one of the removable panels
that give you access to the two furnace compartments. That would show
how it's wired, if it even has a switch. If it's only 8
years old, it may not have a thermostat switch for the blower. Newer
ones are just timed to go on X secs after the furnace fires up. If
it has a switch, it's located somewhere near the top where it can measure
the plenum temperature.
Your G26 is high efficiency furnace with at least 92% efficiency. When
it fails(going down with over heat) you should read trouble code.
Two LED indicators blinking. There must be inside the furnace cover
panel, you should have a trouble code chart or in your owner's manual.
When you say you keep the fan running from furnace side. Are you
jumpering G and R terminal on the control board thermostat interface
terminal strip? If so Did you try same from your thermostat side?
Trouble-shooting requires logical steps. 3 things to check is in order
is thermostat >> wiring from thermostat to furnace >> control board.
Good luck. Also check you warranty some comes with 10 year warranty.
Our furnace came with 10 year P&L warranty.
On Monday, March 9, 2015 at 4:19:00 PM UTC-4, Tony Hwang wrote:
How would a fault in either the thermostat or the wiring to the
thermostat result in the furnace starting, firing, the fan not coming on,
furnace safety then shutting the furnace down? And similarly, how would
a fault in either of those explain the fact that the fan works with
the manual fan selection at the thermostat? Every furnace I've seen,
if that problem description is accurate, the problem has to be at
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