My heater worked like a charm this winter. I recently turn on the air. I have a honeywell thermostat ct8775c. When the fan is in the AUTO position it won't turn on. The fan will turn on if in the 'ON" position though.

Wireing was done this past winter.

I noticed this

Red wire is connected to the R - There is a jumper between the R and Rc
The rest of wires are correct

Green to g
Yellow to y
White to w

WHy does the heater work in the auto position but the a/c won't?

Could be a loose connection in the thermostat that turns on the auto portion of the thermostat.

Switch the on - auto switch several times putting a little pressure against the switch, it may not be making connection.

Probably the cooling fan relay on your control board.

How do you fix that cooling fan relay?

It runs fine on the auto position with the heater on

In the heating mode there is a different switching system than in the Air Cond mode.