Hey all, I've been having an AC problem for awhile now that has been driving me crazy. I have a decent unit that came with my house when we purchased it. The whole unit is about 4 years old right now and has been giving me weird problems.

It seems like the fan doesn't circulate the cold air through the house all the time. Sometimes everything works fine, and when it does the air comes out nice and cold. I used to keep the fan on Auto and thought that might be the problem. Recently I started setting it to "On" but it shuts itself off every now and then. This whole time I'll have the AC set to "Cool" and that will be on, along with the outside unit, but it doesn't blow anything out the air vents in the house.

I tried getting a new thermostat to see if that may be the reason. I went from an old one that came with the house to a digital Honeywell RTH7400 thermostat. It doesn't seem like changing it has made a difference, it still just shuts off every now and then. I cleaned off everything in the interior unit, checked all the pipes, and anything else I could think of but still haven't found the problem.

I talked with an AC guy in my neighborhood and he said it may be a fan relay problem. Could this be it? I don't want to spend a lot just to find out that's not the issue. If it is though, is a fan relay something I could do myself? If not how much should it cost? He told me it's about $130 to have it done by someone. If this'll definitely fix the problem then I don't mind, but if there's a cheaper way, or another possible solution please let me know.

A fan relay should not go bad in 4 years, but it can happen. Fan relays are integrated in the furnace boards which can be expensive in modern day furnaces. In some furnaces the relay is built into a fan center and could be cheaper.

Since the tstat did not fix it and if the heat works fine, I might be inclined to look for a loose connection, particularly on the G terminal at the furnace. So loose connection, fan relay and furnace board (if equipped) are possible options from low o high cost.

Loose wire on G, damaged wire on G are possibilities. You can eliminate a damaged wire/loose wire by disconnecting G at the furnace and connection G to R at the furnace.
If the fan does not shut off, you 1) either solved it or it's between the furnace and the t-stat. If it shuts off it's in the furnace.

Intermittants, in general, are tough to fix.