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SteveTheBuilder 06-21-2008 02:46 PM

2 Stage AC with older Furnace?
I have a 5 year old Keeprite Furnace (91% eff rating) and have a purchased a new AC unit. The Problem I have is the AC unit is 2 stage but the furnace is not. What are my options? Should I replace my furnace with a two stage unit or could the old one be upgraded in some way to get these two to work together?

geo fan 06-21-2008 05:40 PM

not needed
2 stage air handlers that are matched to 2 stage airconditioning are variable speed fans not 2 stage fans this means they ramp up to full spead but operate at full speed regardless of the stage of the condenser . the only exception that I know of on a split system is the 23 seer Maytag IQ drive these system require matching fans and controls. 2 stage furnace's again operate with one fan speed in heat and another in ac but hace 2 sets of burners 1 stage 3 burners fire 2 stage all five or 6 fire. that being said I beleive its everybodys responsibility to get the most eff system they can aford. but you will be fine with your furnace and enjoy your new ac.
ps there is a company call intellidyne the make controlls that can be retrofit to just about any system ac-gas-oil-geothermal. that will reduce energy costs by 10-20%

sgthvac 06-21-2008 09:15 PM


It sounds like your salesman hosed you, unless you really wanted 2 stage AC. You are losing your effiency if you don't match the AC with the same brand variable speed furnace. Variable speed meaning DC controlled motor not multi-speed blower meaning 3 or 4 speeds. That being said as geo man stated it will work.

geo fan 06-23-2008 06:37 PM

again i apologize but you are wrong the variable speed motors are set to static pressure peramiters not a set rpm they are much more eff then a standard motor but do not affect the heat tranfer rate of your ac they are asc. with the seer rating usualy acounting for .5 -1 seer variable speed can be set to many different fan speeds but once they ramp up (under a min.) they operate at 1 speed for cool one for heat and usualy a very low fan speed for fan or circ.
and if the person would read my previous post you clearly dont have the best system in the world (geo thermal) but it will work just fine . you did not get hosed as long as they replaced the evap coil the ac system will operate exactly as designed

dondelson 07-18-2008 12:20 PM

2 Stage Condenser/1 Stage Furnace/2 Stage Thermo - Need Wiring Help
I have a 2 stage condenser (5 Ton Goodman), 1 stage furnace (Goodman) and 2 stage thermostat (Honeywell VP). Since the furnace does not have a Y2 terminal, I have connected the Y2 from the condenser directly to the Y2 terminal on the thermostat. I have been able to get the condenser to work in only one of the two stages (thermostat is configured correctly). I am attaching an AS-IS wiring diagram. Could you please provide help on how to wire this so that both stages will work? Thank you!

geo fan 07-18-2008 08:04 PM

time delay relay
buy an adjustable time delay relay ($3) take your y1 terminal from your furnace y1 to y1 and y1 to the relay and from the relay to y2 get an adjustable relay and set it as high as you can 10 min

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