We have an older bryant furnace It heats up but the fan runs on and on there is a switch that says summer fan when its on it runs constant if you switch that off the fan won't blow at all help needed soon thanks Michelle

When you say older how old 20 years or more or 10 years and less? The older furnace used a fan limit switch to bring the blower on the newer ones used the logic (time delay) in the control board to bring on the blower. I do not know of this summer switch-- is it on the thermostat or furnace?

I really don't know the age of it but the summer swich is right on the furnace I have no idea what its for its just summer and off one switch. The furnace heats up but when the blower doesn't come on the furnace goes out but if you leave the summer switch on it will blow the heat but it doest shut off till you switch it to off

I do know its doesn't have a safety on it for the pilot and doesn't have electric ignighter the gas guy told me that stuff

I had a 50 year old Armstrong furnace and it had a summer/winter switch on the furnace limit control. This was apparently a leftover from when there was no AC and the thermostat did not have a FAN position. It was pretty much disabled when the AC was added or it selected the fan speed. I forget.

If the fan continuously runs then the likely cause is a stuck blower relay. If it's a real old furnace then it's the fan control center which contains a transformer and relay.

The control you are talking about is the old style Honeywell fan and limit control.

It is OK to let the unit run in the on position so you will have heat until the control can be replaced.

It is a two part control with various insertion length for the sensor end.
THis control is also a furnace safety control so the replacement should be done by a professional to prevent improper connections of the wires thst might prevent the furnace safety from operating as it should. All the old Bryant furnaces used them as well as many other brands.

This is probably not the exact control you have but follow this link below for a picture of one. It also has a white on and off switch in front.

5" Honeywell Combination Fan & Limit Control L4064B2228 - eBay (item 250190396794 end time Mar-19-08 18:24:33 PDT) (http://cgi.ebay.com/5-Honeywell-Combination-Fan-Limit-Control-L4064B2228_W0QQitemZ250190396794QQihZ015QQcategory Z109481QQrdZ1QQssPageNameZWD1VQQ_trksidZp1638.m118 .l1247QQcmdZViewItem)

It kind of looks like that picture in the link you sent but doesn't have that switch on it it has wires instead