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vcp 03-20-2008 02:44 PM

Carrier Infinity fan always on
I recently had to repair our Carrier Infinity furnace with a/c since it wouldn't heat. The tech from the company that installed it in 2001 replaced the control board and the blower module. Since then, a week and a half ago, we have noticed that the fan is on low all the time. The thermostat is set to auto fan mode and it is not heating. We don't mind having the fan on all the time, but would like to be able to control it ourselves.

The tech left the old control board, so I compared the settings on old to the new. There are some differences in the small switches and I am wondering if anyone can tell me if these are causing the condition. There are 3 small red switch blocks, one block with 8 on the left and two blocks with 4 switches each on the right. Here are the settings on the old board:
The values on the 8 are: off, off, off, on, on off, on, on.
The values on the top 4 are: on, on, off.
The values on the bottom 4 are: off, on, on.

Can you help with that?

HvacWiz 03-20-2008 05:08 PM

If you look on the back of your furnace door it should tell you what the switches are for, I think the small red block switches are for settings for the a/c tonage you have the other is for the blower cfm. Cant remember off hand what all 8 are for on the other block, I know switch 4 is for emergency heat, #2 is for bypass humidifier. But none of these will make your fan run all the time. If your furnace is not heating but the fan is working you either have an open limit switch your a blown 3amp fuse on your circiut board.

vcp 03-20-2008 06:05 PM

Next step?
Thank you for the response.
The fuse is good.
The furnace heats when needed.
I'll have to ask why there is a difference between the old and new A/C settings and make sure it is set correctly.
What else could cause the fan to run under these conditions?

HvacWiz 03-20-2008 06:19 PM

Do you have a humidifier, if so what is the setting on your stat, there is an option that will control the operation of the fan motor. Push the humidity button and then you can cycle through the options by pressing the mode button, that is if you have the stat I'm thinking of.

statman 03-20-2008 08:04 PM

Just a the fan switch on your thermostat set to auto?....He may have also connected a speed up to a continuous terminal on your board, if your furnace has one.

vcp 03-20-2008 08:24 PM

Fan always on
We don't have a humidifier, so I don't think there would be anything there that would keep the fan running. Is there? How would I find out?

The thermostat is set for Auto fan operation. If I turn it to the FAN ON setting it runs the same as under Auto setting.

What other settings or components could cause the fan to run all the time?


statman 03-20-2008 11:08 PM

Either your serviceman hooked up or set up the board improperly , you are getting 24V power on the furnace G terminal or this board is still not working properly.
I dont have your proper M#, etc. but I dug around and found this list of infinity furnaces. Check into the document/ downloads and you may be able to get some help.,00.html
Hope this helps....if it doesn't, why not just call the serviceman and explain to him what has been happening since he installed the board....should by all means be a warranty situation if he caused the problem.
Hope I can provide some help.

vcp 03-21-2008 08:11 AM

Thank you for your help!

I'll call and get him out again.

The web site you mentioned was helpful. I noticed that there is a PC based software that allows them to troubleshoot the furnace and it's controller boards. The serviceman didn't use it, but I'll ask about it this time.

Thanks again,

vcp 03-26-2008 04:10 PM

The company sent out their best repairman.
The controller board was bad so he replaced it again.
He also set the control board switches correctly.
He told me that secondary controls normally can't harm the main control.
It is running very well now.
Thanks for a great forum!

ro9beam2002 06-05-2008 08:42 PM


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