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Gen 07-28-2010 02:14 PM

No AC installed, is it possible to leave gas furnace blower on?
Hello all,

this is my first post on this forum! I currently rent a bungalow built in the 60s, being a previous appartment-dweller I have a few dumb questions about some of the appliances! :D

The topic for today shall be the gas furnace. It is a Carrier Performance 93 that uses natural gas and a blown air system, and it performed admirably at keeping us warm through the winter. Sadly there is no central AC installed by the owner of the house, and now that it is summer we feel this lack sorely after a few recent heatwaves!

(I'm getting to the point, I swear.) When discussing this issue with a friend, he told me that even without AC it should be possible to leave the fan on (without heating) in order to circulate the air through the house. The basement usually being delightfully cool (despite its ugliness) this sounded like a wonderful proposition, which alas I have failed to implement since I can't figure out how.

We have a digital thermostat upstairs (Sears brand). It has the following buttons: time, prgm, run, hold (the last two have 'fltr' underneath) and switches: fan (on/off), system (cool, off, heat). I thought that setting the switches to fan ON and system OFF would set the fan on without heat, but this does not seem to accomplish anything (no fan noise from the furnace, no air circulating through the ducts). I then thought perhaps there would be a button on the furnace, but the only switch I can find is the gas supply.

Was my friend lying? Or is my thermostat not hooked up correctly? Or am I just too dumb to figure it out? :confused:

I am more than willing to take pictures, but since this is not my house (rental) and I am a chicken I will not mess with wiring!

Thanks in advance for your help.

kok328 07-29-2010 05:19 AM

No, system "Off" disables everything including the fan.
you can run the fan without the heat (so to speak) but, with having no A/C, I would have to speculate as to whether the necessary wiring exists. So this is what I would advise you to do.
Set the thermostat to "Heat" mode and set the tempature as low as it will go.
Then flip the fan switch to "On" and the fan should run constantly.
If not, then some wiring adjustments will have to be made and this too can be accomplished in several different ways.
Just let me know what happens and we'll cross that bridge if necessary.

Gen 07-29-2010 12:56 PM

kok328 - Thank you for your help. I have done as you suggested (set the Temp as low as it will go that is 7 degrees C, fan on, heat) and nothing happens even after several hours.

I should add I have in the past tried the various combinations of fan on/auto and heat/off/cool but never managed to get the fan to work on its own. If I set the temp above the current temp in heat mode then I get heat and that's all I can get it to do! Frustrating.

kok328 07-29-2010 03:07 PM

Ok, then lets try this. Behind the thermostat or inside the furnace where the thermostat wires connect to a terminal strip, jumper the Red & Green wires together and see if the fan comes on. If so, then you can simply connect those two terminals together with an insulated wire that has aligator clips on both ends. Probably best to do this inside the furnace rather than leaving your thermostat hanging off the wall by it's wires.
If not then your fan is being controlled by the circuit board or limit switch which would tell the system when to start/stop blowing air to prevent a nuisance draft of cold air.

Gen 08-10-2010 01:48 PM

kok328 - Thank you for the suggestion but as we are renting I do not want to modify any of the existing wiring. We'll hopefully be buying a house in a near future and can get out of this stuffy place!

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