Help with Atic portion of A/C unit

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Old 06-22-10, 05:49 PM
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Help with Atic portion of A/C unit

Hello everyone,

I am in need of some clarification, before I go out and possibly spend a lot of money. I have been told by a few individuals that my unit in the atic (the blower portion) can have the fan speed increased so it will push more air out the vents. Is this true? Here is all the data I could get off the side of the unit:

Bryant
Product# FY4ANF042000AAAA
Model# FY4ANF042
Volts: 208/230
HP:1/2
Motor FLA: 2.9
Puron: Checked yesterday and is completely full.
Outside portion of unit was also checked and is functioning properly.

The reason I ask is because my house has a 3.5 ton unit, for a 2000sqft, with two zones, one for the bonus room upstairs and one for all of downstairs. It seems that each time both zones are on, the unit just can't catch-up with the heat outside. I feel that if the blower was pushing a little more air, the house would cool off a little quicker. Any thoughts, suggestions, recommendations? I am short of replacing the unit with a larger unit, but I am not convinced that is the smart thing to do.
 
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Old 06-22-10, 06:12 PM
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You really need a competent refrigeration mechanic to asses the unit and do a heat gain calculation to be able to know where you stand.

An a/c system is normally designed to flow 400 cfm for every ton of cooling through the evaporator coil.
This is the amount of air that must be delivered out of the sum of your ducts and grills.
You can not arbitrarily increase or decrease air flow.
It is possible that you don't have this much airflow with your current system.
It is also possible you do have this airflow and your system is undersized.

A good refrigeration mechanic should be able to sort this out for you.

BTW, how exactly is your system zoned?
 
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Old 06-22-10, 06:14 PM
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Does the air feel cold? We more typically use 4 tons in S Texas, similar conditions as Georgia, except you probably have more shade trees. If you have a variable speed blower there are switches in the furnace unit that tell it what speed to run at diff times, but a single speed blower...no dice. Perhaps leaking ducts, a clogged indoor coil. The 3.5 tons would probably suffice if there were no other problems.
 
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Old 06-22-10, 06:35 PM
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srercrcr - Yes the air is cold and how do I find out if my blower is variable speed?

GregH - I had the company technician that installed my a/c check it out; however he did not perform the heat gain calculation you suggested. My house is zone 1 for downstairs and zone 2 for upstairs (1 &1/2 bedroom, approximately 500sqft). It is controlled my a panel which is upstairs and was shown to me as basic on/off operations. They showed me what the LEDs meant when each zone was operating or was off. So what your saying is that I should have approximately 1200 cfm, based on the 3.5ton unit? How can I calculate this? Can it be done based off of one vent? I am really trying to cut the cost of getting an HVAC guy out, but if that is what needs to happen then so be it. I just want that to be my last resort, especially if there are things I can do as the home owner. How can I check the coils you referred to? Thanks for the info guys.
 
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Old 06-22-10, 06:54 PM
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A manometer should be used to measure your external static pressure before changing the fan speed.
If the fan is set to high speed and you have a low ESP, you can blow water off of your evaporator coil and into your ducting (and onto your ceiling).

An adjustment to the barometric bypass, commonly found on motorized zone damper systems, may also be required.

 
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Old 06-22-10, 07:26 PM
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How long have you had this house? Did you have this problem last year?. There are many problems that can cause the house hot, But increase the fan speed on an existing house to fix this problem is rare.
 

Last edited by clocert; 06-22-10 at 08:44 PM.
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Old 06-23-10, 08:47 AM
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The house is exactly 4 yrs old and every year it seems to progressively get worse. Like I talked about earlier, if either the downstairs or upstairs are running alone, the rooms cool off rather quickly. However; when both zones are on and trying to cool, the air flow is cut in half, if not more. When you put your hand up to the vent, you can barely feel the air, but as soon as one of the zones shuts down, then the air flow picks back up. This is why I had the idea of increasing the fan speed in order to push more air. I am stumped as to why the first year we had the house, it seems to cool ok, but the older it got, the worse it became. Now Houston204 mentioned about blowing water off the evaporator coil. I opened up my unit upstairs last night and I presume the coil you are referring to is at the intake end of the unit. Puron flows through the coil, cooling the air and the fan unit pushes it out throught he duct work. I will try and sketch a diagram on how my unit is put together and see what you all think. Will post in a moment.
 
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Old 06-23-10, 11:12 AM
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I can't get my sketch to attach, so I will explain the best I can. If looking at the unit from the top view, I have two intakes(one on each side coming from downstairs and upstairs), one dampener(located on top of unit, same end as intakes running the length of the unit and connecting into the exhaust tube) and finally the exhaust. I was talking with another friend at lunch and he suggested that the dampener the company installed may be cutting down the amount of air flow. He suggested removing it and only having the one exhaust and see what happens. (The only reason it was put in was to keep the vents from sounding like a gale force wind when the upstairs zone came on. Thoughts.
 
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Old 06-23-10, 11:18 AM
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If you want an image to appear here you need to post it on a free site like Photo Bucket and provide a link.
There also a button above when in the reply mode you can paste the link and have it appear.
Make it 640 wide or less so we don't have to scroll.
 
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Old 06-23-10, 09:24 PM
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I'd advise you not to remove the barometric bypass (dampener).
When you only have a demand on the smaller zone you will run a very high static pressure, possibly damaging your ductwork.
 
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Old 06-26-10, 10:38 PM
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Your post said...

Your post said that it has gotten progressively worse. That leads me to believe you have a dirty evaporator coil. Can you get a good look at the coil where the air enters it? I assume you checked the filters. If it has gotten worse over time that would be a good guess. If the coil is cold and sweating all the way down then the refrigerant charge should be good.
I would advise against changing the fan speed; you would just be asking for problems.
Sweating in South Georgia...Later, Marty.
 
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Old 07-06-10, 06:38 PM
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Thanks martymartin. I had one friend mention that to me at work and now that you mention it, when I took the side off the unit upstairs the coil did have quite a bit of water in the pan.(Now to me that might be a lot, but I think I will have it checked.) Is it something I can do myself, or should I let a professional do it? I want to save some money, but I mainly want it done right. Thanks.
 
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Old 07-06-10, 06:57 PM
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Here one for you all. I just spoke with a friend who stated my blower unit may be setup wrong. I have looked at a couple of diagrams and they seem to support his theory. My unit has the evaporator coil at the cold air return end and the blower is facing the output end. Now what I am questioning is how my blower is actually setup. In the diagram the blower has the out end facing the evaporator coil and the side of the blower sucking the air in the cold air. My blower has the output end facing the output of the unit and the suction side pulling air through the evaporator coil. Now it seems that it should work not matter which way the blower is facing, but I am not expert.HowStuffWorks "How to Maintain an Air Conditioner: Tips and Guidelines" My unit has the blower facing the opposite direction, unlike the picture in the link attached.
 
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Old 07-07-10, 05:33 AM
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Did your unit ever work right?? JIm
 
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Old 07-07-10, 10:31 AM
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jjrbus, yes the first year was great and like I mentioned before, it seems to be progressively getting worse. Now that some folks have talked about the coils possibly being dirty, I think this may be the culprit. I am going to try and get them cleaned this week and I will get an update to you all. BTW, is there a specific temp that I should be looking for and where in the house should I check it?
 
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Old 07-07-10, 11:25 AM
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I'm not a HVAC pro, not even an amateur, I probably should not be answering posts. But if worked good the first year, it is unlikely it is put together wrong. Unless it was redone at some point.
I have looked at RV roof top AC's that were replaced and I would bet a dollar to a donut the only thing wrong with them was a plugged coil. The filters were filthy or nonexistent and the coils were caked with crud.
JIm
 
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Old 07-09-10, 06:38 PM
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Ok, had the evaporator coil cleaned and it did not seem to help. I spoke with the technician and he stated that he may have to come back and adjust the barometric bypass and something else to allow the air to get colder and flow better. I'm sorry, but I didn't really understand a lot of it. I asked how cold the air was supposed to be and he stated that he could adjust something that would cause the air to get colder before coming out of the upstairs unit, but not too cold causing the unit to freeze up. I have basically turned the up-stairs zone off and the air flow does not seem to increase downstairs much, nor does it get colder. All I know is something has to change, otherwise I will have to start another home loan just to pay the electric bill. I am still open to any and all suggestions, recommendations. I am that point of thinking maybe I need a bigger unit outside, any thoughts on that. I have him coming back out next Tues, earliest appt available. I will keep you all abreast of what is happening. THanks. v/r gadawg
 
 

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