return air question

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  #1  
Old 08-01-09, 04:46 PM
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return air question

We are trying to make some determinations about my daughters AC system, so as to make a decision about "repair or replace". It has not been working well since they added 500 sqft to a 1000 sqft one story home. Cools for a while, but when it is 90+ outside, the compressor shuts down and stays off for maybe an hour or more, then repeat the cycle.

Anyway, it is a 3 ton unit. I have been "suspicious" of a return air problem. I read about a certain # sq inches of return air filter size. She has a 20 X 20 return grill. 400 sq inches might be in the ballpark. BUT, connected to that 20 X 20 register is a 16" diameter round duct, which only represents in the 200 sq inch ballpark. Is is OK to consider just "filter size" or does that duct matter?? As part of the remodel, they moved the furnace unit from a ground floor closet, to the attic. And now return goes through that 16" diam. round duct, about 20 feet!

We have had some people look at it, but so far apparently we are not calling the right people, because they just hem and haw.

She would at least like to be able to call someone in and ask some specific questions and expect a straigt answer!

Thanks,
 
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  #2  
Old 08-01-09, 11:21 PM
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Sounds like the compressor in the outdoor unit is tripping out on thermal overloads. Many things can cause the compressor to do this. Did you check the capacitors, take an amp draw on the compressor, and compare it to RLA? Is the System Overcharged? Undercharged?
Also, I don't know where you live, but 3tons of cooling on 1000 sq. ft. would be quite extreme. did anyone ever do a manual J calculation on the home to size the load?
3 Tons on the current 1500 sq. ft. might be closer, but like I said, these things should be calculated.
The Return being 16" should allow 1300-1400cfm flow through without any problem with only a 20' run.( 400 cfm per ton x 3tons = 1200cfm required)
If "they" moved the furnace from the ground floor, (Vertical position) and put it in the attic, (Horizontal position?) did they make sure the furnace was approved for that application?
...Maybe you check the outdoor unit and find that the compressor shuts off, but is not smokin' hot...not the overloads.
When you put a furnace in the attic, you have to put a secondary drain pan under the unit to protect against damage. When the unit runs in cooling, it makes condensate, and if the drain plugs, flooding happens. Then the pan and the overflow pan get full. I hope someone thought to put a float switch in the pan to disable the cooling...That could cause the compressor to cut out.
Too many scenarios.
 
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Old 08-01-09, 11:24 PM
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Where are you Located? State/City.
 
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Old 08-02-09, 08:32 AM
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Thank you all very much for the inputs.

Poway, CA ( San Diego inland valley area. Augsust days = 95 to 105)

When the system was moved up, a new furnace was installed. It is a new Trane, 80%. There is a pan under it, and the condensate drains to a Little Giant, and there is wiring from the T-stat connected there, so I assume that turns the unit off if the pump doesn't work.

By the way, the pump discharges a tube poked into a hole tapped into the side of the plumbing vent stack, up near the roof. I know that is a no-no, and it on the list of things we have to deal with.
 
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Old 08-02-09, 08:36 AM
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594....
I don't think the condensate into the vent is a problem...seems like I've seen people here say that new installs are being done that way. Just wanted to say, check before going to all the work to change it.
 
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Old 08-02-09, 07:31 PM
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I agree with heat, either the system is low/over on charge.

Is the coil on the unit outside clean?

3 tons should be WAY more enough for that home, unless there is no insulation in the walls.
 
  #7  
Old 08-06-09, 02:20 PM
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I appreciate all the feedback. Here is the latest update on our end today:

We had a serviceman in to evaluate the system. He said the charge was a little high, but he said mainly it was an 8 SEER condensing unit and a 14 SEER coil, and this was probably never going to work right. I was not aware it was mismatched this bad. The coil was installed new last year when they put in the new furnace in the attic. The condensing unit is about 10 years old. It is made by Heil, and was installed shortly after they bought the house, under the "home warranty", so I am sure they did not put in exactly top of the line stuff!
 
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Old 08-06-09, 07:53 PM
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Yeah, with a mix match system, it's not going to work right.

Are you plan on getting a new unit outside to match the coil?
 
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Old 08-06-09, 09:13 PM
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Originally Posted by Jay11J View Post
Yeah, with a mix match system, it's not going to work right.

Are you plan on getting a new unit outside to match the coil?
That is what it is shaping up to. And this contractor says he doesn't do any R22 any more . It is all R410, so I think that means new coil, and probably new lineset?
 
  #10  
Old 08-07-09, 07:37 AM
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Yeah R-22 system may be a hard fine unless a dealer has a unit left over from last year.
 
  #11  
Old 08-09-09, 08:37 AM
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As the saga continues...here is the info on the condenser unit:
Heil Villager model ACS036A2C1
manufacturer # NACS036A2C1

Can you tell from this what the SEER is??

Thank again,
 
  #12  
Old 08-09-09, 12:16 PM
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I can't find any SEER rating on this.. Only thing I could find it was made around mid-late 90's.
 
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