I have a 5 year old Newmac CL 115 Wood/Oil combination furnace with central air connected. When I started the air conditioner this season the blower would not turn on in auto mode. The blower works fine in auto for heat, and I can force it to start with the ON function for A/C. Also, I have two thermaostats, one for Oil, one for Wood. Everything worked fine last season. Any ideas?
Thanks in advance

I have a 5 year old Newmac CL 115 Wood/Oil combination furnace with central air connected. When I started the air conditioner this season the blower would not turn on in auto mode. The blower works fine in auto for heat, and I can force it to start with the ON function for A/C. Also, I have two thermaostats, one for Oil, one for Wood. Everything worked fine last season. Any ideas?
Thanks in advance

Check/test the A/C fan relay and or the setup that is being used to activate the blower fan in the A/C mode.

The only difference between the two modes is that a fan switch mounted on the heat exchanger activates fan in heating mode and a fan relay does this in cooling mode. Trace the G from T-stat, usually the green wire where it ties at furnace. That wire will lead you to the fan relay. The coil may be bad in that relay. It should be a 24 volt coil that you can test with an ohm meter. If open, replace it for about $5.00.

How do I check the relay with a multimeter? There is a black and a white wire leading from a copper coil. Do I check across those two wires? Do I check when the fan is off or on?

You got it. Those are the coil wires that go to plug-on terminals.