Trick for Running Just the Blower on My Furnace?

My 670 sq foot two-story condominium has an evaporative cooler on the roof, a furnace in an upstairs closet (air intake at the base of the closet), an d a two-wire thermostat. There is no independent fan control. The evaporati ve cooler is ducted directly to the upper floor, without using the ducting that the furnace heating system uses in the winter. The cooler just dumps t he bulk of the cool air down the stairwell to the lower level. Opening an u pstairs window does not help much. I would like to run the furnace blower i n the summer time to help even out the cooling of my condo. I am not allowe d to go into the walls. The thermostat wire feels like it's stapled in plac e inside the walls, so I think there's no way I can wire up a three-wire th ermostat with an independent fan control. The furnace closet has an on-off switch for securing power to the furnace. For the summer time, is it okay t o disconnect the multi-colored wire bundle going to the furnace control boa rd and use the on-off switch in the furnace closet to turn on the blower as needed? The wires to which I am referring appear in the top middle of this photo:
https://i.ytimg.com/vi/GTHY9A7n7K4/maxresdefault.jpg
I discovered this possibility this weekend. I had removed my furnace's blow er for cleaning. When re-installing the blower, I accidentally did not plug in the multi-colored wire bundle. The blower ran constantly without heat u ntil I figured out my mistake.
As an aside, in the three condos/houses I have owned over 20 years, I had n ever cleaned the furnace blowers. I did the taxes for an HVAC technician th e other week, as part of a community service gig. We were chattering about HVAC design as I did his taxes. He said cleaning the blower was some of the best major preventive maintenance one could do for a furnace. This weekend , I went at it. My condo's blower was filthy -- full of dust, dirt and fluf f. I took it outside, both vacuumed and blew it out with low-pressure air, sprayed Simple Green on the blades and wiped them, and used a lot of Q-Tips . Then I re-installed it. What a difference. The air the furnace blows is n ow odorless. There seems to be less dust in the condo, and I think it warms up more quickly.
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Hi Elle,
On 3/10/2016 4:54 AM, snipped-for-privacy@gmail.com wrote:

Most thermostats have several wires *at* the thermostat that allow individual aspects of the heating/cooling to be controlled *at* the thermostat.
Said another way (in your case), most furnaces expect those "many wires" to govern how they operate! In your case, <someone> has saved on wire and just implemented a "demand for heat" function at the thermostat.
If you look *in* the furnace, you will typically see (some subset of) connections labeled: C (Common) E (Emergency heat) G (biG blower/fan) O/B (heat pump reversing valve control) R (poweR) RC (poweR for Cooling) RH (poweR for Heat) W (heat -- I'll let you come up with a 'W'-based mnemonic! :> ) W2 (second stage heat) X (auXillary heat) Y (aYr conditioning) Y2 (aYr conditioning second stage)
These are *supposed* to be color coded but too often, cables don't have the right set of colors available, etc. "Wire is wire..."
[Of course, there are variations and no telling how yours may, in fact, have been wired!]
You'll undoubtedly find your two-wire thermostat ties several of these "inputs" together.
If you isolate the "heat" connections ("open" them with a switch), you should be able to get the furnace to run its blower WITHOUT trying to provide heat.
You can also try to *trick* the furnace by disconnecting other signals inside the unit -- but, you run the risk of the processor (I'll bet yours has a "PIC" in it) deciding that something is wrong and triggering an error/shutdown.
[The advantage to JUST commanding the blower on is that the furnace thinks it is doing exactly -- no more, no less -- what you want it to do!]
Model number of furnace might be able to shed more light on specifics. Or, details of how the inputs are actually wired, in your case.

Replace filters frequently (they're cheap) and you'll prevent all that crud from getting in there in the first place!
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On 3/10/2016 4:54 AM, snipped-for-privacy@gmail.com wrote:

Open a *downstairs* window. Cooler pushes air through the house (else the house gets overly humid in a matter of minutes) so give the air a "way out" that causes it to have passed through MORE of the house.
[Unfortunately, coolers aren't designed to be reversible; otherwise, they could be excellent "whole house fans" -- open windows on the ground floor at night, turn on cooler and let it draw cool air up through the house, exhausting the hot air that has risen to the upper levels!]
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For the summer time, is it okay to disconnect the multi-colored wire bundl e going to the furnace control board and use the on-off switch in the furna ce closet to turn on the blower as needed? The wires to which I am referrin g appear in the top middle of this photo: https://i.ytimg.com/vi/GTHY9A7n7K 4/maxresdefault.jpg

Yes, you could connect from the RH to the G(fan) terminal at the furnace, then use the AC power switch on the furnace to turn the fan on and off. Or you could wire a low voltage switch between those two terminals and use it. How much it will help even out the cooling is questionable though.
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Don Y and trader_4. With your directions, I think I have a few options. I a gree it's best if the CPU on the furnace control board sees only a "fan on" signal.
Don Y, it is a Carrier 58PAV furnace, and I have the manuals for it, includ ing a good wiring diagram. I change the filter every few months. But I just bought this roughly 20-year-old condo 11 months ago. I doubt the furnace b lower had ever been cleaned. I have tried opening the downstairs window, bu t then, with the weight of the cold air, the path is pretty direct and tend s to miss the upstairs bedroom. It's the upstairs bedroom that gets kinda h ot in the summer, even with the upstair bedroom window open a bit to draw t he cool air.
trader_4, I am not optimistic but think it's worth a try. The downstairs ha s a single air register, in the ceiling. In the summer I will close this do wnstairs register, open fully the two upstairs ones, and then run the furna ce blower.
Thank you both. :)
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On 3/10/2016 11:37 AM, snipped-for-privacy@gmail.com wrote:

Note that you probably have some option switches ("DIP switches") on the control board that give you some ability to tweek the furnace's response (within reason) -- at the very least, there is usually a range of settings governing how long the blower will continue to operate AFTER the thermostat STOPS calling for heat (to cool down the heat exchanger inside the furnace).
You should be able to isolate the 'W' lead (in summer, no heat required) and let the 'G' lead activate the blower when the thermostat tells it to do so (i.e., you'll just be using the thermostat as a "switch", not really a temperature control -- keep that in mind if it doesn't support cool/heat modes).

Ah, you're stuck with the sins of previous owners.

What I learned with the swamp cooler was that you had to tinker with how much "vent" you had in each room -- to encourage the air to flow in particular ways. If there is no way for air to *exit* a room (out a window), then the room sees very little cooling.
So, *crack* the windows in all rooms that want to be cooled. Then, open the farther rooms a tad more. It's an iterative process until you understand how your house behaves...
You have to ensure you don't let all the air out in the "wrong" places (depriving other places of cooling in the process).
When you are done, opening a door part way should just barely cause the door to close itself (air pressure). If it slams closed, then your air flow from the cooler is greater than your sum total "vents" can handle. If it doesn't close at all, then you are letting too much air out the vents.
[Note that this will change based on outdoor conditions as well as fan speed on your cooler]
Presumably, you're someplace that has *4* seasons. Here, not so much. OTOH, only 364 more days of summer!!
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On 03/10/2016 01:04 PM, Don Y wrote:
[snip]

I remember something about 4 seasons: nearly summer, summer, still summer, and I can't believe it's not summer
--
"A stupid man's report of what a clever man says can never be accurate
because he unconsciously translates what he hears into something he can
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On Thursday, March 10, 2016 at 12:06:05 PM UTC-7, Don Y wrote:

Don Y, thanks for the exacting tips. I will give them a try.
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Hi Elle,
On 3/13/2016 2:44 PM, snipped-for-privacy@gmail.com wrote:

Good luck! I was frustrated for my first two seasons, here (having lived in places where cooling was accomplished by DE-humidification instead of humidification!). And, most "locals" only know what to do, not *why* (so you can't extrapolate their advice to YOUR situation).
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What kind of attic do you have, if any? Is there a trap door in your ceiling leading to it. During warm weather, late at night is the time to look, just before dawn, or on a cloudy day. Maybe more insulation in the attic would help.
On Thu, 10 Mar 2016 03:54:02 -0800 (PST), snipped-for-privacy@gmail.com wrote:

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On Saturday, March 12, 2016 at 1:28:47 PM UTC-7, Micky wrote:

It's a flat roof on an adobe building. I looked for a trap door in the ceil ing; no luck. No way is the condo management going to let me mess around on the roof. I bet I could cut a hole in one of the closets right about where the thermostat wire runs, but this is more trouble than I want to go to at the moment.
The good news is that the thermostat is only about five feet from the penet ration into the furnace closet where the thermostat wire feeds to the furna ce.
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