Need help diagnosing cooling problem - possible airflow issue?


  #1  
Old 07-06-09, 05:57 PM
A
Member
Thread Starter
Join Date: Jul 2009
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Need help diagnosing cooling problem - possible airflow issue?

Hi everyone,

1st post here, read thru quite a few threads and I know there are some knowledgable people here that can probably help me out.


Short story:
2 year old goodman furnace, old AC was 21 year old Rheem, 2.5 ton unit. Now just replaced with new 2.5ton Weather King. New unit, coilset, and A-coil.

Previous problem:
Unit was constantly running and couldn't keep the house cool. If it was 85 outside, the house wasn't any cooler than 80, and thats with it running all day. After installation of new AC, the problem basically is the same. This is a split level house, and there was never great airflow to the upstairs, but now I have to put my hand ON the vent covers upstairs to even feel the airflow at all. Could the blower in my goodman furnace not be strong enough to handle the house? Maybe the new A-coil is too restrictive?

Additional details:
Located near Cleveland, OH
House is split level, built in 1961, 1650 sq ft.
Furnace is in basement. Main plenum has 5" ducts feeding the lower rooms in the house. A rectangular 8x23" duct feeds the upper rooms. There are 18 total house vents (but I keep the one in the garage closed off, as well as 2 in the family room, and the 3 in the basement). The family room is on the first floor, and is always cool. The living room is 1/2 flight up, and this is where the thermostat is. It has a high ceiling (no attic over this portion of house). Another 1/2 flight up are all the bedrooms, which are usually 5-10 deg hotter than the main floor.
I seem to get decent (not great) airflow from the vents on the main floor of the house. The air is pretty cool (but not REALLY COLD).

Furnace is Goodman model GMH80903BNAB
90,000 BTU input, 72,000 BTU output
1/3 H.P blower motor, 10"x8"
it also says on the label:
"tested to 15in external static pressure"
I couldn't find any info on rated CFM, RPM, a pressure chart, or anything like that.

AC is Weather King model 13AJL30A01
R410A unit
13 SEER

I would say the air on the outside unit is only slightly warmer than the surrounding air (maybe 10 degrees?)

I have also had someone pop open the cover on the A-coil and it had a lot of condensation on it but no ice. Also they checked and the furnace blower is set on the highest setting. I've replaced the furnace filter with a new one (and even tried running without it for a few hours but didn't make any difference). I've also tried closing off all the first floor and main floor vents to force the air to the bedrooms, but this didn't work either. Also, there are no dampers in the vents in the basement, I only have control at the vent covers in each room.

OK, thanks for any advice or help. If you need more info. please ask and I will try to get it.
 
  #2  
Old 07-06-09, 06:33 PM
S
Member
Join Date: Sep 2008
Location: Long Island
Posts: 695
Upvotes: 0
Received 0 Upvotes on 0 Posts
so 21 years you went from R-22 to R-410A on the freon.....temperatures readings out on the condenser you should see a 10 rise from the air thru the coil and discharged up and out.on the furnace section 18F drop from the return to the discharge into the hopuse is typical(take filter rack temp and top of unit above A coil)if your short on charge that basically is the tonnage rating compared to a correct charge and cycle on stat setpoint.check those split temps after a 30 minute run on a hot day
 
  #3  
Old 07-07-09, 09:50 AM
dun11's Avatar
Member
Join Date: Feb 2009
Location: Local
Posts: 753
Upvotes: 0
Received 1 Upvote on 1 Post
Did the installing contractor do a load calc?

Did he look at your duct system?

There may be more then one filter, I assume you checked, an attic fan would help maintain an even temp on both floors.

Have you had the installing contractor back out for any problems?
 
  #4  
Old 07-07-09, 12:12 PM
C
Member
Join Date: Aug 2008
Location: Texas, California
Posts: 1,405
Upvotes: 0
Received 6 Upvotes on 6 Posts
Sounds you have air flow problem. As you mentioned, you can not even feel the air from the unstair vents. This is definitely a problem. you will have to check the duct that carry the air to those rooms to see if they are blocked, or they are simply too small. Second, check the air temperature that come out the downstair vent (check the one with strongest air flow), to see if the air temperature is at least 15 degree lower than your room temperature at that time. If you have at least 15 degree difference there, then your A/C unit is probably OK.
Also, don't close too many vents, that will restrict the total air flow which will damage your fan and cause A/C freeze. Good luck.
 
  #5  
Old 07-07-09, 04:03 PM
A
Member
Thread Starter
Join Date: Jul 2009
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Temps:
OK, I measured some temps around 6:30pm this evening, after the unit was running for 1 hour plus. The thermostat was set at 72 deg.
Outside temp: 69 deg.
Outside hot air exhaust: 80 deg (right above fan)
Inside house temp, first floor: 69 deg
Inside house temp, middle floor: 71-72 deg (near thermostat)
Inside house temp, upper floor: 76 deg
Return air temp: 70 deg (right at furnace filter)
Discharge air temp: 51 deg (right above A-coil)
Discharge air temp at various house vents: 55-56 deg

It seems the temp differentials are fairly normal? So that means the AC is working OK?

Also, I do have a powered attic fan that is on a thermostat. I've played with the temperature settings on that (anywhere from about 90 to 120 or so) and it hasn't seemed to make much actual difference.

Ductwork:
I know there are 5" ducts to all the lower floor vents (I can see these in the basement). I understand 6" or 8" are more common?

But the vents to the upper part of the house must all run off the one rectangular vent (8 x 23) that goes up thru the walls and across the garage ceiling. (I have 2 bedrms above garage) I can't tell what size ductwork runs off of that and down to the individual vents in each room. (Although I would assume it is the same as the basement). That ductwork is all enclosed in the ceilings/walls and I can't get to it to inspect it. I did pull one vent cover off the large 8 x 23 duct in the basement, and checked it with a flashlight, I couldn't see any sign of obstruction or blockages.

Contractors:
The furnace was put in just before we bought the house, 2 yrs ago, so I have no idea about that. Seeing what I am seeing now, I am afraid the previous owners put in the cheapest new furnace they could just to sell the house, or the contractor undersized the unit drastically? Could the blower not be sized correctly to deal with all the backpressure from the ductwork? The strange thing is that I don't remember having a problem heating the house the last couple yrs. (although it could be because heat rises to the upper levels?)

With the AC contractor, he's been out a few times, and says the AC seems to be working OK. He's not sure about the airflow, if that's the problem or not. He has NOT done any load calcs, etc... though. To tell you the truth I'd rather find the problem myself and then determine the best course of action (fixing it myself or going back to a contractor, etc...).

Is there any chance, if it is the blower, that I could get a more powerful blower that will swap right into the same furnace? I've googled the part number on the blower but didn't find a whole lot of info (other than direct replacements)

Thanks everyone so far, your input has been very helpful to me.
 
  #6  
Old 07-07-09, 06:46 PM
C
Member
Join Date: Aug 2008
Location: Texas, California
Posts: 1,405
Upvotes: 0
Received 6 Upvotes on 6 Posts
Looks like your A/C unit is OK. Now your fan, is it a new fan ? or 21 year old fan. Needs to check to see if the fan needs to be replaced. Don't put a larger one unless you know the size limit of your A/C and Furnace. They all have to match. Now your upstair rooms above the garage. Since the garage is not cooled, so it is very hard to keep the rooms above garage cool, most people have this problem unless when you built the house, you put extra extra extra thick insulation under those rooms. Since the house was built in the 60s, I really doubt you have good insulation in there. So, I believe your main problem is not enough air go to upstair, may be the duct is too small, or may be too many turns which weaken the air pressure. not only you need good air flow to upstair, you need a very strong one because of the garage issue. I had a house with a above garage apartment, I had the same issue even my air flow was Ok. I ended up bought a large window unit to compensate the situation. You see you can not tear up everything to redo the air duct and the in-wall insulation. So window A/C was my way (not a perfact way) to deal with this
prblem.
 
  #7  
Old 07-07-09, 07:50 PM
HVAC RETIRED's Avatar
Member
Join Date: May 2008
Location: Wisconsin USA
Posts: 664
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by Albigger View Post
Temps:
OK, I measured some temps around 6:30pm this evening, after the unit was running for 1 hour plus. The thermostat was set at 72 deg.
Outside temp: 69 deg.
Outside hot air exhaust: 80 deg (right above fan)
11-F Split. Again, what SEER is it; matching coils?
That is too low a split, depending on SEER Rating!
Evaporator may not be absorbing enough heat to transfer outdoors!

Are the blower wheel blades perfectly clean, is the evaporator perfectly clean all the way through it?


Inside house temp, first floor: 69 deg
Inside house temp, middle floor: 71-72 deg (near thermostat)
Inside house temp, upper floor: 76 deg
Return air temp: 70 deg (right at furnace filter)
Discharge air temp: 51 deg (right above A-coil)
19-F OK there

Discharge air temp at various house vents: 55-56 deg

It seems the temp differentials are fairly normal? So that means the AC is working OK?

Also, I do have a powered attic fan that is on a thermostat. I've played with the temperature settings on that (anywhere from about 90 to 120 or so) and it hasn't seemed to make much actual difference.

Ductwork:
I know there are 5" ducts to all the lower floor vents (I can see these in the basement). I understand 6" or 8" are more common?

But the vents to the upper part of the house must all run off the one rectangular vent (8 x 23) that goes up thru the walls and across the garage ceiling.

How many SA vents upstairs?
The 8x23 is only 184-sq.ins.


(I have 2 bedrms above garage) I can't tell what size ductwork runs off of that and down to the individual vents in each room. (Although I would assume it is the same as the basement). That ductwork is all enclosed in the ceilings/walls and I can't get to it to inspect it.

If you remove the diffusers,you will see the boot & might be able to tell if its a 5" duct coming to the boot.
A 5" duct is awfully small.


I did pull one vent cover off the large 8 x 23 duct in the basement, and checked it with a flashlight, I couldn't see any sign of obstruction or blockages.

Contractors:
The furnace was put in just before we bought the house, 2 yrs ago, so I have no idea about that. Seeing what I am seeing now, I am afraid the previous owners put in the cheapest new furnace they could just to sell the house, or the contractor undersized the unit drastically?

A properly operating 2.5-Ton A/C system with a proper functioning duct system & airflow should cool your home, if not it needs weatherization.

Could the blower not be sized correctly to deal with all the backpressure from the ductwork?
Could be!

The strange thing is that I don't remember having a problem heating the house the last couple yrs. (although it could be because heat rises to the upper levels?)

In the heating mode the temp-rise split is much higher, so it could heat OK but not cool OK.

With the AC contractor, he's been out a few times, and says the AC seems to be working OK. He's not sure about the airflow, if that's the problem or not. He has NOT done any load calcs, etc... though. To tell you the truth I'd rather find the problem myself and then determine the best course of action (fixing it myself or going back to a contractor, etc...).

Is there any chance, if it is the blower, that I could get a more powerful blower that will swap right into the same furnace? I've googled the part number on the blower but didn't find a whole lot of info (other than direct replacements)

Thanks everyone so far, your input has been very helpful to me.
The ductwork system is very suspect.
You need a velocity meter to check airflow.

The 18 Supply Air Vents would need to average 1,666-BTUH each to deliver 30,000-BTUH.

They could possibly do that even with 5" ducts.
However, there is a problem in the cooling mode!
 
  #8  
Old 07-08-09, 07:03 AM
dun11's Avatar
Member
Join Date: Feb 2009
Location: Local
Posts: 753
Upvotes: 0
Received 1 Upvote on 1 Post
As stated, its very difficult to cool rooms above a garage for obvious reasons. Where is the stat located in relation to the return?

I think your 1st step would be to do a load calc, once you determine if the system is sized right you can move on to other possibilities...........its all guess work at this point.
 
  #9  
Old 07-09-09, 04:06 PM
A
Member
Thread Starter
Join Date: Jul 2009
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
see replies in red

Originally Posted by HVAC RETIRED View Post

11-F Split. Again, what SEER is it; matching coils?
13 SEER AC. Not sure what you mean about matching coils? How can I tell?
That is too low a split, depending on SEER Rating!
Evaporator may not be absorbing enough heat to transfer outdoors!
That makes sense

Are the blower wheel blades perfectly clean, is the evaporator perfectly clean all the way through it?
I assume the evap is clean, it was brand new in box. I can pull the blower and check the wheel, I haven't cleaned it since we've been here (2 yrs).

Inside house temp, first floor: 69 deg
Inside house temp, middle floor: 71-72 deg (near thermostat)
Inside house temp, upper floor: 76 deg
Return air temp: 70 deg (right at furnace filter)
Discharge air temp: 51 deg (right above A-coil)
19-F OK there

Discharge air temp at various house vents: 55-56 deg

It seems the temp differentials are fairly normal? So that means the AC is working OK?

Also, I do have a powered attic fan that is on a thermostat. I've played with the temperature settings on that (anywhere from about 90 to 120 or so) and it hasn't seemed to make much actual difference.

Ductwork:
I know there are 5" ducts to all the lower floor vents (I can see these in the basement). I understand 6" or 8" are more common?

But the vents to the upper part of the house must all run off the one rectangular vent (8 x 23) that goes up thru the walls and across the garage ceiling.

How many SA vents upstairs?
The 8x23 is only 184-sq.ins.
6 vents upstairs (feeding 3BR and 1 bath), with 3 returns, however I can't really feel any flow going back into the returns. I feel a pretty strong return air at the only return vent on the middle floor, which is only about 10ft of ducting away from the furnace. Also this floor (middle) is where the thermostat is.

(I have 2 bedrms above garage) I can't tell what size ductwork runs off of that and down to the individual vents in each room. (Although I would assume it is the same as the basement). That ductwork is all enclosed in the ceilings/walls and I can't get to it to inspect it.

If you remove the diffusers,you will see the boot & might be able to tell if its a 5" duct coming to the boot.
A 5" duct is awfully small.

I popped off one of the covers and they are 5" ducts.

I did pull one vent cover off the large 8 x 23 duct in the basement, and checked it with a flashlight, I couldn't see any sign of obstruction or blockages.

Contractors:
The furnace was put in just before we bought the house, 2 yrs ago, so I have no idea about that. Seeing what I am seeing now, I am afraid the previous owners put in the cheapest new furnace they could just to sell the house, or the contractor undersized the unit drastically?

A properly operating 2.5-Ton A/C system with a proper functioning duct system & airflow should cool your home, if not it needs weatherization.

Could the blower not be sized correctly to deal with all the backpressure from the ductwork?
Could be!

The strange thing is that I don't remember having a problem heating the house the last couple yrs. (although it could be because heat rises to the upper levels?)

In the heating mode the temp-rise split is much higher, so it could heat OK but not cool OK.

With the AC contractor, he's been out a few times, and says the AC seems to be working OK. He's not sure about the airflow, if that's the problem or not. He has NOT done any load calcs, etc... though. To tell you the truth I'd rather find the problem myself and then determine the best course of action (fixing it myself or going back to a contractor, etc...).

Is there any chance, if it is the blower, that I could get a more powerful blower that will swap right into the same furnace? I've googled the part number on the blower but didn't find a whole lot of info (other than direct replacements)


The ductwork system is very suspect.
You need a velocity meter to check airflow.

The 18 Supply Air Vents would need to average 1,666-BTUH each to deliver 30,000-BTUH.

They could possibly do that even with 5" ducts.
However, there is a problem in the cooling mode!
I measured the ducting run going to the upstais, it is:
8x23 (184 sq in) rectangle for 8ft, 90, 15ft, neck down to
8 x 18 (only 144sq in), 90, 9ft, 90, ~15ft
this is where the 5" round ducts tie into, of course using another 90, and then run about 18ft to the room vents.

Sounds pretty restrictive to me. I haven't come up with a way to measure the air velocity yet, but it is pretty low upstairs.

The ducting for downstairs rooms is all 5" round duct right off the main plenum.

I did find my blower info:
http://www.goodmanmfg.com/Portals/0/...-2/SS-GMH8.pdf
Looking at pg 7 for my GMH80903BNAB unit, it looks like I have a 3 ton blower at .5" ESP.
Also lists 1593CFM at .1", 1561 @ .2", 1567 @ .3", 1543 @ .4"
1493 @ .5", and on down to 1230 @ .8".

Anyway I can tell if that blower is enough? What would be the best course of action?



@ dun:
I understand about the garage rooms (and the whole upstairs). I keep the garage closed when the AC is running when possible.

The thermostat is about 5ft off the floor of the middle room, the main return vent is right at the floor, about 3 ft. over.

I haven't looked in depth at all the heat load calcs, but most require to know the type of insulation in the walls, attics, etc... which I don't think I know all of that. Do they have one for a "typical" 1960s home. I can go around and do all the measurements and calcs but I need the actual form or program.

Thanks.
 
  #10  
Old 07-11-09, 07:56 PM
A
Member
Thread Starter
Join Date: Jul 2009
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
At the recommendation of a family friend who used to work in the field, I installed some dampers in the ductwork feeding the lower portion of the house.

After throttling the lower vents, I did get some more flow to the upper rooms, and it seems to have helped the house be more uniform in temperature. However it still seems like I should have more flow overall.

Also, it was 80 deg outside today, I turned on the AC at 1:30pm when it was 74 in the house. It ran for 8 hours to get the house down to 72 deg! I know the newer units are supposed to run longer instead of cycling too often, and it was probably 80% humidity today, but still that seems very excessive.

I also found out the duct that runs thru the garage to feed the upstairs rooms is not insulated (it is framed in and drywalled, but that's all). So I'm sure that's not helping.
 
 

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