Help with troubleshooting central A/C... fan will not stay on

[dscheck]

My air conditioning won't come on. When I move the thermostat to "cool", the outside unit turns on , but the fan inside does not. Putting the thermostat's 'fan' setting to "on"  yields nothing.  I checked the switch on the furnace: the fan comes on when I move the switch from off to on, but it does not stay on, even with the thermostat's fan setting is "on." It looks like there is power to everything. Is there anything else I can try to get this thing going myself before I call a technician for service? Thanks

[JWWebster]

Your furnace probably has a bad relay. The fan blows on low for heat but needs high for cooling. So they install a fan relay in the system to do so in most units. You obviously have 24 volts because you can make the fan come on so the transformer is good. The fan blows so i would say it most like ain't the capacitor. It aint electric heat or heat pump because the fan would blow on the correct setting no need for a 2 speed configuration on electric heat. I would say it is a bad relay or at least look there first. Read my page on relays complete with pictures:
http://sites.google.com/site/sublimeappliancerepair/ask-the-sublime-one-a-question/blade-removal-101/old-motor-has-3-wires-replacement-motor-has-4-or-more-wires-wtf/central-unit-fan-relays

[snknby123]

What switch at the furnace are you using to turn the fan "on"? And when you say it turns on but does not stay on does it turn slowly then to a complete stop?

On my unit I could hear the relay kicking in and I was able to measure 115v to the high speed (black) wire to my motor. It would spin up slowly then fade to a stop and my coil froze as a result.

If this sounds similar to your situation start with the "Run" capacitor that is usually mounted near the control PCB or follow two leads from the motor that go to a little silver box. Find a HVAC supply store or a store that sells motors, generators etc and purchase the run capacitor and install it.


I just did mine and saved me $500 cuz I know the HVAC Tech would have sold me a new motor let us know what you come up with

[tmh]

Thank you very much.  My friend could figure out how to connect them.  It's great to have A/C working summer in South!