AC Evaporator Coil Question

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ex0r

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Hello there everyone! I am an avid DIYer, and while I am able to do most things, there is something that is baffling me that I cannot seem to figure out.

I have been looking at installing a central air unit ontop of my furnace, that was replaced brand new about 7 years ago (just before I moved in). My furnace is a Goodman Model #GMH950904CXAD it says it supports up to 90k btu. When looking at coils for it, it says it should be able to accommodate 2 to 5 tons.

I have looked at at least 6 different AC units, and so far I have not found any that fit ontop of my furnace. All of the ones within specification are too tall and too wide. Now, normally I would install a transition at the top of the furnace to transition to the evaporator, but I already don't have enough vertical room to where my duct work starts at to allow that. I've attached a couple of pictures to show you what I mean.

20200703_105912.jpg

20200703_105925.jpg

In the top picture, the top of the diffuser is at the top of the picture. To the right of that is a horizontal vent that connects to the main heat venting of the house. The problem, is that there is no additional room above it as the vent connects to the side of the diffuser, no the top of it.

Every coil I have come across, in measuring, has been too tall (as well as mostly too wide). That is, the top of the coil is beyond where the horizontal venting comes into the furnace at, leaving me no room to be able to install a transition to cover the difference in width, and surely not enough room to connect an elbow at the top of the evaporator to connect into the horizontal duct work.

Does anybody have any suggestions aside from tearing up all the ducting on how I can fix this?
 

Sparky617

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I have found that buying HVAC parts without being an HVAC contractor can be very difficult. Several years ago my blower motor went out. The local distributors wouldn't sell me one without being a contractor and it isn't exactly a stock item at Lowe's or Home Depot. I did find one online, but it cost me $100 to have it shipped. I'm pretty handy and DIY many things. I have a good HVAC contractor I've been using since I replaced that blower motor. He's been keeping my nearly 22 year old units running ever since. We're probably going to replace the units this fall. They are definitely showing their age and just this week I had to put 2.5lbs of refrigerant into my downstairs unit. Last month the upstairs unit needed a new set of contacts on the compressor relay. All told I put about $600 into the two units this season.

So I don't really have any advice other than you may want to find yourself a good, independent HVAC contractor. Many of my neighbors use ARC, all of them have replaced their units, some 7 or 8 years ago. Over the course of those 8 years I might have spent $2000 in annual tune-ups and repairs. I'm way ahead of them cost wise. ARC is really good at selling new units.
 

geochurchi

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Are you looking at “A” coils or flat coil? the later will take up less space, unless you have a vacuum pump to evacuate the system once installed you may be better off having it installed, also warranty may be an issue if you do it.
Geo
 

pjones

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Just because your furnace says it can do it doesn’t mean your ductwork is capable of all those sizes. In addition to that, if you under size it you will never be happy and if you over size it you will get a short life from your compressor and likely not be very comfortable for the time it is working.

I recommend having an hvac contractor perform a heat load calculation and inspect your ducts to see what options you have that will work for you.
 

pjones

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Did they fix the leak before adding the refrigerant? Or at least find it?

Contractors are a normal wear and tear item. They are a cheep part and shouldn’t really be looked at to determine the overall health of your system. Depending on where the leak is may determine if the system is worth saving or not. If you are adding refrigerant then there is a leak somewhere or it is making its way out of the system somehow. You should not have to add refrigerant unless there was something that happened that caused it to exit the system.
 

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