modifying a 1 speed furnace into a 2 or 3 speed


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Old 05-27-08, 05:55 AM
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modifying a 1 speed furnace into a 2 or 3 speed

Ok my intent is to get some feedback on this prototype design for changing a 1 speed lennox g8q4 -150 9e furnace with a/c and hrv from a 1 speed medium spd unit into a 3 speed capable item


First the speed control 120 volt system looks like this



to mod this to 2 speed with white rodgers 90-370 relays fla 12 I came up with this design


my question is - the control of the relay is handled by Call to Cool ? or is there a better way ?

I assume heat and cool are never called at the same time

This is the 3 speed prototype design



Again colntrolled by Call for Heat W with override by the temp control device and a lock out form winter time operations

Is Call for heat the way to do this ?
Can a fan switch from ie low spd to hi spd without problem if done instantaneously by relay ?

I was going to check the speed setting for my york a/c coil and unit once i get the info on that to look into the blowing of water off the coil during cool problem , if it exists -- who knows maybe its supposed to run on high .. then maybe it would cool both floors on the house and not just the lower floor

Thanks
 

Last edited by geoimpala; 05-27-08 at 06:14 AM.
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Old 05-27-08, 06:19 AM
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Honestly, I wouldn't spend anything on the furnace. G8 has to be around 20 to 30+ years old, and are know to have cracks in the Duracurve Heat Exchanger.

When was the last full heat exchanger inspection on the furnace?


Also that furnace may very well be way over sized.
 
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Old 05-27-08, 06:28 AM
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The tech did inspect last winter ...

plus I have 2 co2 monitors that are not indicating anything yet

house is 3000 sq ft temp gets to a real -30 C at times in winter
the furnace was one of the last one's built in Canada in 1991

then all these realys and stuff would not cost more than 200 hundred dollars --as I'm thinking of replacing with a trane 80%
unit but am not convinced of the total loss cost of this furnace yet..


I did find this
The G12 is getting up in age. The way that you are describing the pilot flame pulling away when the burner shuts off sounds like it may though not necessarily be a crack(s) in the heat exchanger. The blower is still running and would be pushing air into the chamber. The Duracurve heat exchanger cracks at one usual location. In the back of the chamber to the left of the seam in the are of the curve. If you see rust discoloration left and right of the burner cover this is an indication that hot combustion gases are being pushed out of the burner chamber. Any good service technician that is familiar with the Lennox duracurve heat exchanger would be able to inspect the furnace for safety.



my burner does not look like this , but I'll double check

I think it's the post Duracurve type heat exchanger

ps house needs new roof shingles first

Can you tell if your furnace has a Duracurve exchanger by serial number?

K found this http://www.secinfo.com/dsvrp.64qv.htm

We have offered
the owners of all Pulse furnaces installed between 1982 and 1990 a subsidized inspection and a free carbon monoxide detector. The inspection includes a severepressure test to determine the serviceability of the heat exchanger
 

Last edited by geoimpala; 05-27-08 at 07:18 AM.
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Old 05-27-08, 07:30 PM
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Originally Posted by geoimpala
This is the 3 speed prototype design

What's the red and blue drawing?? Wire from t-stat?
 
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Old 05-28-08, 07:45 AM
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Actually that is my question too--

The G green wire for fan goes to the fan control that exists now and controls on/off and auto

my question as well as yours is that I am asking weather using the Y (a/c) cool line ( in blue) to activate the a/c fan relay would be a proper thing ? (yes its from the t-stat)

ie the same W (heat in Red ) line for the heat speed relay activation?

How do they do this in most systems now ?

Thanks again
 
 

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