A/C Blower Not Working

[Clark Addison]

We have a bi-level HVAC system in our house. I haven't had the top floor turned on for a few weeks due to the mild weather, but a few days ago it really started warming up, so Friday evening I turned the upstairs A/C on. When I turned the thermostat down, the A/C unit outside turned on as usual, which is normally followed within a minute or two by the blower turning on. The blower never turned on, though.

I switched it over to the furnace to see if that made a difference, and it didn't; still no blower. The furnace/blower is up in our attic, so I went up to take a look. It sounds like something is happening. When the blower is supposed to go on, it makes a noise and something starts up, but it's not pushing air to any of the vents.

I checked the breakers to make sure nothing was amiss, but didn't know what to look at beyond that. I'm just posting it here to see if anyone knows of some basic or simple things I should check before calling the repair guy tomorrow.

[NorthwestUteFan]

Does it click, buzz, or otherwise make noises, or does the blower motor actually turn? If it makes noise but doesn't actually start turning then I would suspect a bad capacitor. If so, it is a cheap and easy fix. Do you see any obvious loose wires or 'messy' electrical components? Capacitors 'pop' and the black, sticky electrolyte can ooze out.

The fact that it won't start up for the heater points to a problem with the fan startup circuit, or possibly the motor controller.

[mtnbiker]

It sounds like something is happening. When the blower is supposed to go on, it makes a noise and something starts up, but it's not pushing air to any of the vents.

There are two fans at work. When the furnace starts up, a smaller fan runs to get positive pressure up the flue. You don't want outside pressure pushing the exhaust gases back into the house. Then the furnace attempts to light the burners. If the electronics detect correct and consistent flame, then the main blower also starts up and pushes air through the house.

It sounds like you're getting the flue fan on, but nothing else. You can turn the furnace off and on to try to reset it, and do a little wire jiggling, but it might be better to call an HVAC guy. The furnace is one place you want to err on the side of caution.

[chrisrenrut]

Our furnace has two flashing LED lights, and the sequence and speed at which they flash tell you if things are normal, or help troubleshoot problems. There is usually a label or panel that will list what the flashing pattern means. Do you know if your furnace has a similar system, and check to see if it tells you anything about the problem?