Hi! Our central AC is working great but we'd like to have the blower (fan) going 24/7 to keep things recirculating. The problem is that even when the thermostat fan setting is switched to ON, the blower fan won't run. Apart from that, the AC works completley fine and follows the thermostat temperature settings no problem. I'd appreciate some help diagnosing the problem.

I've read various things about relays, capacitors, thermostats, etc. but I'm not sure where to start. I'll have to double check but I think the furnace is a 10 year old Carrier Weathermaker 58MVP and we have a Honeywell touch-screen programmable thermostat.

Thanks in advance for your assistance.

If at thermostat red(power), and green(fan), yellow or blue may be for compressor contactor(For Cool). White may be heat.
If for my own house, I would connect green to the red. Will not shut off.
I don't know if code allows to run full time? to do for someone else.

Has the fan ever run 24/7? The stat may not be correctly installed. Call these guys and ask for a diagram to confirm wiring. Programmable Thermostats - SAVE on Honeywell Programmable Thermostats

Just to avoid confusion, I'm not looking to hard-wire anything to run non-stop forever. The long and short of it is that I just want the fan to run and it's doesn't, even when set to "ON" at the thermostat.

It definitely used to work and is usually set to "ON". It was just the other day when I noticed that there was no air being recirculated between AC cycles.

Suppose I connect the red and green wires together at the thermostat and the fan still doesn't come on (haven't tried yet but will later). What could that indicate?

Yep, I would not hard wire either. Green to red at the stat and the blower runs means a bad stat. Green to red and still not running could be a bad relay on the board, I doubt that there is any motor issue, just a control issue.

Any idea what it typically costs to fix up a relay problem? Ballpark of course.. expensive, cheap, quick, complicated, easy, etc. Even better would be if I could do it myself but I don't know what's involved in this. What would you suggest? Is it a DIY or definitely not a DIY? I am semi-handy.

The problem is almost certainly in the thermostat. The A/C uses the same green wire, relay, capacators, etc. as fan ON. For fan ON, the thermostat switches power from RC, maybe RH, to the G terminal. For A/C it switches power from RC to Y and G. I guess it would be possible ON uses RH and it isn't getting power. Unless you have 2 transformers, RH and RC are jumpered.

Relays used to be a cheap, easy replacement. When the one for my furnace blower died, I coughed up $300 for a new control board.

Since, if it is working, you run the blower continuiusly with the flick of a switch, I would hope it doesn't violate code.

Even if thermostat woriking correctly, and set to cool, Fan shuts off for normal operation,
You wouldn't want to switch to fan only, every time cooling cycle stops. Toggle switch at air handler could connect red to green, and could even be connected to a timer, for day only operation?

I would start at the thermostat, as labman posted above, when you switch the thermostat to cool, it sends 24 volts to y and g, it has to be in the thermostat. Simply remove the cover, twist the red and green wires together, if the blower comes on, it's in the thermostat.

Thanks for the analysis. I'll try this out. Seems strange though that an expensive Honeywell thermostat would fail so quickly. It's top-of-the-line (for whatever that's worth) and just over a year old.

Well, I have seen them all fail, it may just be in the switch. If it's that new, and you find that it is the thermostat, you may want to check and see if it has any warranty.

Much to my dismay, I only have 3 wires into the thermostat. R, W, and Y (which is actually colored blue). Since there is no G wire, that would make me think that the thermostat can't control the blower ON/AUTO. Is this right? I'm positive I had the fan able to run continuously in the past. Is it possible to have the fan running ON but only when it is providing heat and not when in AC? Is there something on the furnace to manually set the fan to ON? Maybe this was only happening during the winter. I'm either confused or going crazy. Hopefully someone can set me straight.

I'm not sure why they don't have the "G" terminal hooked up, they have to cross it somewhere, otherwise the fan wouldn't come on for air conditioning, the connection must be made in the furnace, if this is the case you can't run the fan manually. The button you are talking about at the furnace is the fan/limit switch, this is for heat, it's like a thermostat, when the burners kick on and the temp. is brought up in the furnace it kicks the blower on. You can push that button in, but it will be running on low speed.

So, in order to have the AUTO/ON control at the thermostat actually function properly, would it be as easy as just running a new wire from the thermostat G to the furnace G?

Yep, you are better off just pulling a new 4ct wire between the furnace and thermostat.

Thanks for everyone's assistance. You've all been a great help.

No problem, that's why we are here, come back anytime!

Yeah, it is easy to pull a cable through an interior wall. If it wasn't stapled inside the wall, you can use the old one to pull the new one in.