How does AC coil affect air distribution?

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Old 03-23-18, 07:31 PM
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How does AC coil affect air distribution?

I had to replace my furnace the other day. When the hvac guys were installing it they noticed the ac coil in the plenum was either too large or too small (I really didn't catch what they were saying). They said that the air going to the upper floors was being severely restricted. Am I being dealt a load here or can the size of the coil affect air distribution? He did show me the coil or whatever pointing out an area that seemed to be open but only about 1/3 the size of the entire plenum area (geez I hope I'm using plenum correctly!). Anyway, I would really appreciate some thoughts on this. Thanks.
 
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Old 03-23-18, 07:40 PM
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Welcome to the forums.

The A/C evaporator coil is in the furnace plenum. It sits directly in the airflow. The furnace should have in its design enough airflow to deliver rated output thru that coil.

Too large and it wouldn't fit and too small would allow air to pass by and not get cooled. If it is was too small I couldn't see how it would impede the airflow.

If it was plugged by dust or corroded shut then it needs to be cleaned or replaced. This is really a matter to be discussed in more detail with your installer.
 
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Old 03-24-18, 03:54 AM
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Your description of the coil set up is a bit confusing,

an area that seemed to be open but only about 1/3 the size of the entire plenum area

Do you mean there is an opening next to the coil that allows air to bypass it?
If so 100% of the airflow must pass through the coil.

Can you post some clear pictures that show the set up?
 
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Old 03-24-18, 05:32 AM
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Sorry but I can't get a photo as they buttoned everything up. I guess my real question is can the evaporator coil interfere with the air flow during the heating season? I see Pjmax says no. I will wait for installer to come back. They said they need to wait for temps to rise because they have to remove the refrigerant from the system before swapping out the coil. I wanted to be prepared for when they come back.
 
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Old 03-24-18, 09:22 AM
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Why are they changing the coil unless it was bad before they started the work or damaged by a careless worker. Are you having the whole air-conditioning unit replaced as part of the job. If they are replacing it due to a restriction they are probably dealing you a load of crap. The coils do not get restricted for no reason. I would be there inspecting when they come to replace the coil and ask questions. If they damaged the coil during the furnace installation then they should be responsible for the replacement. It's too bad you have to be so careful today. When I was in business I never took advantage of a customer.
 
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Old 03-25-18, 06:51 PM
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Thanks Steamboy. I will definitely be paying close attention but I think I'll ask a few questions before they start the work.
 
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Old 03-30-18, 08:25 AM
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Got an update. The issue is that the coil is N-shaped and when it was originally installed they decreased the opening into the coil to increase efficiency ratings/reasons. They were saying that with an A-coil and regular opening it would increase airflow down the coil and through the system. I noticed that there is not a lot of air coming from the registers, especially on the second floor. I see this is an area of dispute on the net, especially the a vs n-coil debate. Thoughts?
 
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Old 03-31-18, 02:46 AM
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These coils were called slope coils or slant coils where I am from. I rarely used them but when I did, I had no problem with air flow thru them. The free area thru this type of coil usually was about the same as that of a same capacity sized "A" coil. Without being able to see the whole system, furnace, ducting of supply and return air and duct sizes I cannot comment on the air flow to certain rooms. I doubt the problem is the coil, although it could be. I would lean more towards the duct work or fan/blower speed being the problem. I would ask them to "guarantee in writing" that changing the coil would solve the air flow problem they are saying you have and if changing the coil doesn't fix this problem that, that work would be TOTALLY FREE. See what they say, This would be a test to see how certain they are as to their expertise. (Remember the comment about the load of CRAP).
 
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