Changing blower speed on furnace & air handler
Last week the tech was out for the annual servicing on a new install last year of an am std 2 stage variable speed furnace (auy080r9v3w6) in the basement and a trane 15xl a/c system with a variable speed air handler in the attic 4tee3f49a1000a).
Heating: The second stage (the one that comes on first) blows too strong and I asked the tech if he could turn down the blower speed on this stage. He didn't seem overly familiar with the unit, and after looking at the informaiton on the panel, he worked out how to change the speed on the first stage and said that the blower speed on the 2nd stage could not be changed. I later looked at the manual, and it seems to indicate that the blower speed on the 2nd stage can be lowered. Is this correct? If so, I'd like to call the back out. The thermostat is 2 stage and is wired to control the stages.
A/C: I was concerned that the a/c was oversized at 3.5 tons for a 1750 sq foot/2 fllor house, even though it is a bit leaky. Contractor said that he did calcs and that it was borderline 3/3.5 (other bids were for a 3 ton). As the unit cycles a bit often and the air is a bit more humid than I'd like, I think that the unit is oversized. I asked the tech if he could reduce the blower speed on the air handler, and if this would help this situation. He said that the variable speed unit should find the right level. Is this correct?
The second stage should not be the first one to come on. Second stage means second in line...first stage is the primary stage.
If the furnace has an ECM motor, these motors are variable speed in the sense they adjust speed to accomodate real time duct static pressure. Depending on the control logic of the thermostat, furnace or air handler, it could also stage blower speed for dehumidifying or for more sensible cooling. As it is, there may be dip switches for your model that can be set to determine the amount of air the blower delivers either all the time or at a particular stage, if it is set up to be staged.
What is the normal temperature you like to keep in your home in summer?
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
In the summer we set the thermostat to 70. The thermostat is in the upstairs hallway. Downstairs is consistently 3-5 degrees cooler, but I don't think there's anything to do about this,short of an expensive zoning.
Regarding the furnace: Not sure why, but what Am Std calls the second stage is the first stage to come on. Second stage is rated at 73,000 capacity and first stage at 49,000. The second stage kicks in first and runs until the temperature at the thermostat meets the set temp, and then the lower first stage kicks on at a nice gentle speed. When the second stage comes on it is overpowering in terms of air flow and is noisy. It is this stage that I'd like to have them lower if possible. Again, the tech said that the second stage couldn't be changed but the installer's guide that I later looked at clearly shows that the dip switches can be changed to lower the air flow. Although it looks straightforward to do, I don't like messing with it myself, and want to call the contractor back out to do this. But before I do, I want to make sure it is possible, since he said it wasn't. He was saying this, however, based on the information in the furnace cover, he didn't have the installer's guide and didn't seem familiar with this furnace even though his company installed it last year. I'd like to handle this soon because my 1 years service contract ends soon.
if your calc says your in between then it may have been smart to go under sized. however you should be able to easily make the 3.5 run like 3.0. Ive never heard of second stage coming on before first. I dont think your tech has any training in this area you need them to send someone with experiance maybe with that guy so he can learn to.
when he come bacl give him the installers guide......it's likely that he doesn't have memorized the dipswitch settings. i know i don't. then again i haven't done residential stuff in a while. most of my dipswitching is used to address vav's and such. lol
Second stage coming on first, kind of defeats teh purpose of a 2 stage furnace.
Sounds like something is wired wrong.
Call tehm back, tell them of your concerns. Ask for a tech that has training on 2 stage systems.
Your VS won't find the right speed, it has to be set on the board.
You might want to ask about the Honeywell IAQ thermostat for your 3.5 ton A/C, the IAQ can keep the blower at a lower speed if the humidity is high in your house.
1. if there is a large temperature set back it will probably run on second stage first, normally 4 degrees or more. Are you setting it back at night or while at work.
2. most variable speed units of that size will do from 3 to 5 tons so it is critical to set the dip switches up right or you will be blasting 5tons of air through your duct
3. is that 15seer a two-speed outdoor unit? if it is then it should run at a lower tonnage in first stage maybe 2-2.5 tons most of the time except on really hot days, so oversizing should not be a problem.
4. there is probably a trane guy on this board that give you more specifics
on a side note: i'm confused. A furnace in ther basement? but an air handler in the attic? One themostat? set at 70 making it 65-67 downstairs? are you living in a wine cellar? Humidity problems at 65 degrees? are there two duct systems or one?
Thanks for the feedback.
duxinaroe: The furnace in the basement and the air handler for the a/c in the attic are two separate systems, each with a thermostat. All contractors had said that the existing duct system for heating would be insufficient for cooling, so we put the air in the attic, with 3 drops to the first floor.
A/C air handler is variable speed, but not 2 stage.
beenthere, secondtech, and shophound: That the first to come on is called the second stage is confusing, but I think that it is set up correctly. The "second stage" has more capacity (73,000) and comes on first for a faster job of bringing the temp down and then first stage (49,000 capacity) comes on second for a slower longer run. Isn't this correct that the stronger stage comes on first?
I'll call the installer back and ask them if they have someone with more experience with these units. The installers were serious and customer service oriented, but I'm not convinced they're up to date. I discovered this board during the install, and I had them switch the single stage thermostat to a 2 stage. Would I be better off calling in a company that I know can make the changes? I'd have to pay, but would this be better than having the same company out to figure it out on my equiptment?
Yours is the first that I heard of that second stage(high fire) comes on first.
The Trane version doesn't work that way.(its the same furnace)
The idea of 2 stage is for longer run times. It should start in low fire first, if the thermostat enses the temp dropping while in low fire it calls for second stage(high fire).
Have the installing company come out. They are the ones that will be providing you with warranty. Unless your ready to switch companies for all work.
If you do the set back, then yes the furnace will go into 2nd stage right away.. But if the set point been left alone, and then furnace should only run 1st stage.
Ideal of two stage is quiet run time. 2nd is for recovery, and if the system is falling behind on a cold snap.
What's the A/C model # at the outdoor unit?
Regarding the furance, I'll ask them to come back out to set up the furnace so the stages respond in the proper order and to change the settings on the 2nd stage.
Regarding the variable speed air handler: duxinaroe and others say that the 3.5 ton variable speed handler can be set to run at a slower speed. Is this correct? I'd like to ask for them to do this if it is possible, but I'd have to request a different tech to come out.
I may also take beenthere's suggestion and ask for a Honeywell IAQ thermostat. Would this help with overall comfort as well as give better temp control?
If I do so, I think I'd get another company to for the thermostat, to change the settings, and to provide future servicing.
I think you are jumping the gun with the talk of getting another company to do work on a new system. Just call the installing company and ask them to send someone that knows (or can figure out) these systems. Not every tech in our company is intimately familiar with them. They are relatively new and not what they see every day. Training classes will only take them so far until they start seeing them more and more.
Originally Posted by lojay
The first stage should definitely be the first to come on, unless as was previously mentioned, the temp is being changed manually several degrees below the existing temp. Think of a car. You don't press the gas pedal all the way on the floor if you are driving on flat ground in town. Need to go up a steep hill or to pass someone on the highway, then you give it more. Same concept with your furnace and air handler. Low stage handles the basics, the most common temps while the 2nd stage is there for backup when it gets really cold.