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I had a new Bryant 915SB furnace installed 2 months ago. When the thermostat clicks on the blower runs for 4 or 5 seconds, stops and 3 or 4 seconds later the flame and then blower start normally. Otherwise it seems to work well. I asked the installer and he said all Bryants do that yet I can't find any mention of that anywhere. It seems like unnecessary wear and tear.
It's a single stage furnace with a constant torque emc 3/4 hp motor.
Is this normal? If not should it (can it) be fixed?
Just noticed that it seems to happen when the low continuous fan is running but not when I turn the fan off.
Thanks

See attached manual. On page 57, 2(h) mentions the blower running for 90 sec before a call for heat.

In your case it almost sounds like the low speed continuous fan is stopping and switching to the heating fan speed.  It can sound a bit clunky.  Likely the only thing you can do to avoid that is either leave the fan in the AUTO position or wire the continuous fan to the same heating fan speed, but this would use slightly more power.

Thanks
It doesn't run anything like 90 seconds. It seems this is unusual, a friend has a slightly older Bryant and it doesn't do it.

The 90 seconds is usually after the thermostat is satisfied. Those Bryant/carrier units start differently. The 4 to 5 seconds seems normal to me. I've installed tons of these units where the blower shortly before, then the flame starts.
As far as the low fan continuous admin is right