Heater Blower Pulsing

Old 01-23-10, 03:32 PM
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Heater Blower Pulsing

I have a 1990 Heil-Quaker 90+ Nat gas Condensing furnace with a BC-7070-A/M blower control time delay relay.

The relay has 2 dials of "Time On" and "Time Off" with + and - rheostats for 0-4 min (estimated) timeframes. I tried finding instructions on the best way to set this control but am having a hard time doing so.

When the stat calls for heat, the flames come on correctly then soon after the blower comes on and the flames shut down, then the blower shuts down and the flames come back on. This goes on and on until the stat no longer requires heat.

What is the correct way of having the blower for a longer duration rather than the pulsing back and forth between blower and flame?

In older fan blower controls I am familiar you could use plenum temperature to determine if control was set right. I can't get this one correct as it works on time delays rather than plenum temp (except for high limit).

Any help would be appreciated as this is getting me !
Old 01-24-10, 04:25 PM
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Fan timer

Try turning the start delay to a shorter time. Any numbers you can get off the control might help.
Old 01-25-10, 05:45 PM
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When the blower comes on, do you see the flame quiver at all? It shouldn't. If it does, you may have heat exchanger issues that then affects the flame sensor, and shuts the unit down. Observe and let us know, if you come back.

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