[dposch]

Specifically looking for a circuit diagram, with specs.
Technician replaced a 2-stage blower motor but full proper function wasn't returned.
Next he starts mucking about with the thermal switches, replaced one that he dubbed "obsolete", and may have shuffled either of the remaining 2. Regardless, I had no blower at all, even though the gas would cycle and fire.
I checked the wiring and it looked to me like he'd missed a connection, so I swapped the 2 leads that looked amiss, and sure enough I have blower now, but only on one stage (low stage, I think).
And the fan comes on after a long burn, then goes off very quickly and often comes back on after another minute or so, only to run very shortly and go off again. But often the gas shuts off during the second fan activation, then comes on again, and pops off shortly after the third fan activation, if there is one.

This thing is ancient, but I'd think the thermal switches and limits would still be available.
Dearborn DVF-65B-N upright natural gas w/2 stage blower. 75% eff.

The sequence when it worked properly was;
Thermostat would trip closed
Gas would open and light with pilot after about 10-15 seconds
Fan would start on low stage after about 30-50 seconds of burn
Fan would kick to high stage after 1-3 minutes
Gas would continue to burn until thermostat tripped open
Fan would settle back to low stage and blow for another minute or so after gas shut off


Currently, sequence is (as described above);

Thermostat trips closed
Gas fires within 15-20 seconds
Fan starts on low stage after 4-5 minutes of burn
Fan runs for 30-45 seconds
Fan starts again on low stage after 1-2 minutes
Fan shuts down after 25-45 seconds
Gas opens/ignites and burns for 15-30 seconds
Thermostat trips open
Fan starts on low, runs for >1 minute
Gas goes off with a small "Pop"

So, I'm seriously thinking he's screwed up the logic of the control circuit, possibly also dealing with failed switches/limits. Not that big a surprise, since he told me he apprenticed HVAC working the sheet metal side of things, only got into the service side about the past 4 years.

[hvac1000]

I have searched all my electronic furnace docs and the only thing I can see is Dearborn space heaters name on the list but no info.Sorry

[dposch]

Le p00p

Pardon my French.
8(