Help, question about Variable Speed Blower

**jayelwin** · 03-30-2008, 10:43 PM

Hello

I am a homeowner and I have recently finished a major renovation on my house. My HVAC contractor installed two American Standard Freedom-90 Comfort-R 12 speed variable speed furnaces in the house. There are 4 levels and each furnace runs two zones, one on each level. Each zone has an Aprilaire 8363 thermostat.

Now I have noticed that the furnaces simply kick on and off like an old fashioned furnace. I do not detect these 12 speeds I have paid extra for. I mentioned this to my contractor and he said he made a few adjustments and now I should detect the different speeds, but I do not think I do. I feel maybe I have the wrong thermostats, ones that do not control the variable speeds. He says it's the furnace that selects the speed, not the thermostat. If the thermostat is set very high above the current temperature, the furnace will "detect" the larger temperature request and blow faster, and if I set it slightly above the current temp it will blow slower. This implies the thermostat somehow "transmits" the set temperature to the furnace. I was not aware that the thermostat could do this.

I would like to make sure that I am getting what I paid for, a multi speed HVAC system. I'm not sure I am. I think it's the thermostats that are wrong. Does anyone know if the 8363 is the right thermostat? Is my HVAC guy correct in telling me how the speeds would be selected? Also how would it provide two different speed requests to the two zones given that each furnace only has one blower?

Please help an uneducated consumer. Thanks.

**BaldLoonie** · 03-31-2008, 06:15 AM

Where does 12 speed come from?

That furnace is a 2 stage meaning it has a high and a low fire. Depending upon the zone panel, the fire rate may be selected by the panel, the thermostats or time up after so many minutes of running on low. You'd have to know how the installer designed it to know how yours will perform. If sounds like he is using the thermostats to pick high or low fire. That can be good or bad as often 1 zone cannot handle all the heat if the furnace burns on high.

**hvac_superman** · 03-31-2008, 06:41 AM

Start with a model number of your furnace.

**beenthere** · 03-31-2008, 07:10 AM

Start with the furnace mod number.
And then the zone panel.
And then the size of the floors/zones.
If the furnace is over sized too much, you won't ever notice it going to second stage.

**mark beiser** · 03-31-2008, 09:22 AM

It isn't a "12 speed" blower.
The variable speed blower and controls have 12 maximum cooling airflow settings available via the dip switches.
Then depending on control inputs, there are 16 steps, from 25% through 100% of the max cooling airflow setting. Very few systems will use more than a handful of the 16 possible steps. I think Trane's zoning system is the only thing that would possibly use them all.

The heating airflow is a separate setting, and on gas furnaces will only run at 2 airflow levels. One for low fire, and one for high fire.

The thermostats in your system just tell the zone control that the zone needs heat, the zone control cycles the equipment. The zone control opens dampers to the zones that are calling for heat, and runs the furnace in low or high fire. There are several ways a zone control could determine whether to run low or high fire, depending on settings and control inputs.
There isn't a way that it could provide 2nd stage to one zone, but only 1st stage to another.

It sounds to me like you have some unrealistic expectations.