york rooftop

[redwhitekat]

Just need some input on a york rooftop unit i came across last week, i did some repairs on the burners and when i got it to fire the indoor fan does not come on, so it trips on the high limit, long story short i changed the hi limit and aux limit in the heat x section, thinking that is what brings the fan on, but no fan also changed the cirquit board, and still no fan, it only comes on when the fan is switched to on on the tstat, wiring diagram is in bad shape, can barely read it, anyone know what i'm missing here ????
M# d6cg048n09906c
S#nlem124427
help would be great

[Dchappa21]

Probally the heat/fan sequencer.... They go bad all the time... Just trace the fan coil wires back to it.

[invisiblecollar]

it could be the t-stat itself. W1 may not be energizing the G circuit. Ive had this happen before.
Did you try jumping R to G? That'll tell you if your stat is no good.

[BFG6868]

it could be the t-stat itself. W1 may not be energizing the G circuit. Ive had this happen before.
Did you try jumping R to G? That'll tell you if your stat is no good.

W1 will not energize the fan control circuit (G) through the tsat unless the tsat is a newer electronic type and the tsat is set to energize the fan in heat mode. In that case the operating limit control or the G command from the tstat will start the fan.

I would think the problem is in the operating limit.

[gztech]

If the schematic is not readable you need to trace the indoor fan motor wiring back to where it's being controlled from...generally from a PC board. The thermostat, as previously stated, does not activate the blower during the heating mode.The HI limits were probably fine and doing what their supposed to do!

[timebuilder]

If I am recognizing your model prefix correctly, there should be a fan sequencer to the right of the compressor contactor. Trace the wires and identify it. It uses a heater and a disc that flexes when heated and closes the fan contacts.

Let us know it you find it. If not, I will try and look it up.

[oldtimer2]

If it is an older York RTU, like time said, there should be a time delay relay next to the compressor contactor. If your trying to start this fan on a cold day, the TDR takes a long time to heat up. If it is a newer York, they have a little circuit board ( TDR ) that controls the fan. Trace the fan wires back to the control panel.