Very weak blower


  #1  
Old 04-06-18, 06:44 AM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
Very weak blower

The lower level (above ground) in my friend's basement is always significantly cooler than the upper levels. I took a look at her air handler, and found that her filter was very clogged. I replaced it, but there has not been any improvement. I checked the ceiling registers (three total) and there is virtually no air coming out. I checked for dampers in the utility room but do not see any. For some reason, there are two return registers about 10' apart towards the floor. One draws a tiny bit of air and the other draws nothing (won't even hold a single ply of tissue paper). I noticed that the air handler is pretty quiet and seems to be in a limp mode of sorts. For instance, if I open the filter cover, it is not drawing nearly as much air as it should. I know when I pull the door/cover off of the air handler in my home, it feels like I'm going to get sucked inside. I realize the blower speed reduces when the heat is on, but this is extremely slow. The unit appears to be original to the house (2000), but it looks like a good unit and otherwise appears to be in good shape. Could it be a bad blower motor? Would dust caked up on the blower wheel substantially inhibit air flow? Or perhaps something has gone awry with the control electronics that isn't allowing the fan to run at full speed? Sorry, but I don't have a make or model. I'm just trying to get an idea if a blower motor can lose 50% of it's capacity without any other symptoms (no strange noises, smells, etc).
 
  #2  
Old 04-06-18, 08:28 AM
S
Member
Join Date: Jan 2017
Location: USA
Posts: 447
Upvotes: 0
Received 14 Upvotes on 11 Posts
Excessive dirt on the blower wheel will certainly limit the amount of air movement. You should also check to see if the blower is running . You could slip a piece of heavy cardboard over the fan housing to make sure the blower is moving a lot of air. Ask your friend if the furnace has always had very low air supply or is it something new. If you have access to an "Amp-Probe", you could check the running amperage of the fan motor. How is the air flow on the upper floors? Can you increase the fan speed by changing the motor wire (tap) to a higher speed? Has anyone serviced or worked on this furnace recently, changed any parts etc.?
 
  #3  
Old 04-06-18, 09:11 AM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
Excessive dirt on the blower wheel will certainly limit the amount of air movement.
It uses a pretty hefty filter, so I figured little to no dust/dirt would make it past. Could be wrong. I really didn't check closely. I noticed the filter was very dirty and told her to replace it. The air purifier unit she has is similar to this one: https://www.aprilaire.com/whole-hous...ers/model-2410.

You should also check to see if the blower is running.
I removed the door from the filter housing and there is air moving, but nowhere near what I feel it should be. The unit is pretty quiet too, which seems odd.

Ask your friend if the furnace has always had very low air supply or is it something new.
She bought the house last year, and wouldn't know the difference. Her bottom/entry level is at least 20 degrees cooler, if not more.

How is the air flow on the upper floors?
I checked one of the ceiling registers and a floor register on the next floor up and hardly felt anything.

Can you increase the fan speed by changing the motor wire (tap) to a higher speed?
Maybe, but I didn't want to mess with it because it isn't my house.

Has anyone serviced or worked on this furnace recently, changed any parts etc.?
No clue. There's a service sticker on the return ductwork with a date of 2002, but that doesn't necessarily mean that is the last it was serviced. The home doesn't appear to have been taken very good care of, so it's possible the unit hasn't been serviced in that long. Could enough dirt and dust gotten past the pleated filter to gunk up the coils and/or fan enough that it would inhibit air flow this much or even damage the blower motor? My experience with bad motors is that they begin to emit a burning smell (which could have already happened years ago), noise, and/or vibration. None of these symptoms are present. It just isn't drawing/pushing nearly enough air.
 
  #4  
Old 04-06-18, 09:50 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 64,939
Received 3,951 Upvotes on 3,544 Posts
You could try checking the airflow when in FAN ON or COOL mode.
Both of those should be a faster speed.
 
  #5  
Old 04-06-18, 10:02 AM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
I had the fan set to ON when I checked it.

She said a technician was just at her house and said the unit is fine, and that it is undersized--"for an apartment" he said. Apparently it was replaced in 2015 to get the home ready for sale. I don't see how any reputable company would intentionally install an undersized unit even if the homeowner asked, but nothing surprises me these days. I don't know the make, but I believe the model is a 315 AAV 036 070 065A. I'm going to see if the motor can be wired for a higher speed, but something tells me it's probably fixed if it's really for an apartment. Even if it is adjustable, would it be counter productive to increase the speed considering it is a heat pump system?
 

Last edited by mossman; 04-06-18 at 10:54 AM.
  #6  
Old 04-06-18, 11:01 AM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
This is the unit she has: https://www.carrierenterprise.com/br...15AAV#tab-info

It's a Bryant 315AAV036070 3-ton gas furnace. 1225 CFM cooling, 615 CFM heating, 300 RPM, 70,000 BTU. I'm no expert, but a 3 ton unit sounds like plenty for a townhome does it not? My single family home is about the same square footage and only has a 2.5 ton, which is plenty. I realize I'm comparing apples and oranges, but it seems like 3 ton should be plenty for a middle unit townhome. Something isn't right.

I'm going to put an ammeter on it this evening and also check the run capacitor. Will post back with my findings.
 

Last edited by mossman; 04-06-18 at 12:39 PM.
  #7  
Old 04-06-18, 01:06 PM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
Some other specs that are noteworthy:

Output capacity (High/Low) is 35,000 / 54,000 BTU
Motor RPM: 300-1300 (heating/cooling)
CFM: 735 / 1180 (low heat/high heat), 1050 cooling

Read something in the spec sheet about a comfort air flow setting, which decreases the CFM by 120. Maybe I'll disable this to see if it improves things.
 
  #8  
Old 04-06-18, 09:43 PM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
Took a closer look this evening. Diagnostic light on control board is normal (constant yellow), voltage to blower is normal (120V), and everything is clean. I measured the current draw on the motor, and it is only 450mA. That seems awfully low. I didn't see a run capacitor anywhere. The motor is a Genteq 1/2 HP ECM 3.0 motor. I can't seem to find a current spec for it, but it seems way low.
 
  #9  
Old 04-07-18, 03:23 AM
S
Member
Join Date: Jan 2017
Location: USA
Posts: 447
Upvotes: 0
Received 14 Upvotes on 11 Posts
This is something that you don't see every day but it has happened. Check to see if the motor is turning the right way and that the blower fan is installed correctly. On a rare occasion, the factory will install the blower fan backwards, or the motor will be running in reverse; it will still blow air but not near enough One last thing, these ECM motors may be above my pay grade since I have been retired for some time. Some of the younger service techs will be along shortly to give suggestions.
 
  #10  
Old 04-07-18, 04:25 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,639
Received 79 Upvotes on 69 Posts
ECM's (Electronically Commutated Motor) are "sophisticated" motors and are quite different from a "regular" motor. They need to be programmed for a specific application and the main control board (what the motor plugs into) controls much of the motor functions. If the motor is running slower than it should be, it's possible that there's a problem with the main board. I'm not an expert on these motors, just a homeowner (and engineer) who has one in my furnace. They are energy efficient and are variable speed, so they can maintain a constant airflow (speed changes to maintain constant airflow). There is a "tester" that can check for proper operation. I know this because when my ECM motor failed (fortunately it was still under warranty), the service tech mentioned that there is a motor tester, although he didn't have one with him.
 
  #11  
Old 04-07-18, 05:16 AM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
I skimmed through the repair procedure on the Genteq website. I'd be surprised if many companies have this equipment, but i could be wrong. I've already told her to call her warranty provider back and have then send someone else back to inspect the system. A 3 ton unit shouldn't be drawing like a bathroom fan.

I checked the rotation amd it is correct. And the cage only fits on one way.

I believe the motors are controlled by a pulse width modulated (PWM) signal, in which case my current draw reading would be off (since the meter is expecting sinusoidal AC).
 

Last edited by mossman; 04-07-18 at 05:38 AM.
  #12  
Old 04-07-18, 12:02 PM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
Apparently I can check the motor health by connecting 24Vac directly to the C and Rx terminals on the motor (via the plug). Not sure if th e fan will be at full speed, but I'm hoping it will increase significantly so I can rule out the motor itself. If the motor checks out, then I'm assuming the only other thing it could be is the control board. I have an oscilloscope, so I could check the control signal, but that probably doesn't make sense since I don't know what frequency and duty cycle the PWM signal should be.
 
  #13  
Old 04-09-18, 09:02 AM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
Found a Youtube video on how to bypass the control board and test the motor. You basically take the 24Vac on the board and apply it directly to the control lines on the motor. When I did so, I got a large amount of air flow and plenty of air coming out of the vents. I connected things back to normal then put the system in cooling mode. I also got a pretty good amount of air in cooling mode. So the weak air flow is for fan mode and heating mode only. I read the manual a little more closely and found that the unit is in a "comfort mode" by default, which decreases the air flow by 18%. This mode can be disabled by flipping a DIP switch on the control board. There is also a DIP switch for increasing the air flow from 350 CFM/ton to 400 CFM/ton, which should give me another 150 CFM (since it is a 3 ton unit). That is 270 CFM total, which should be pretty significant. I'll give it a shot and post the outcome.
 

Last edited by mossman; 04-09-18 at 09:20 AM.
  #14  
Old 04-12-18, 10:31 AM
M
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,913
Received 27 Upvotes on 21 Posts
I disabled comfort mode and I can now feel air coming out of the vents. I'd still like to feel more, so I plan on closing off some registers on the upper floors to increase the air flow downstairs. I also boosted the CF (constant fan) speed so it now blows about as hard as it does in cooling mode. I could already feel the temperature warming up after a few minutes. So....it appears the unit is fine and just needed some dialing in.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: