Replace Central AC Unit a DIY project?

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Old 08-04-19, 12:21 PM
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Replace Central AC Unit a DIY project?

Hi, I've got a 4 ton central air unit that stopped working.

I'm pretty handy and these units look pretty straight forward for parts with a lot of room to work. I'm still not sure if it needs to be fixed or replaced.

1) Is troubleshooting and fixing a central air unit something a typical amateur can handle?

2) I've seen a few units at Home Depot. Any other ideas on where to get these?

3) What's the calculation for how many ton you need? I've got a 4 ton now, but I'd like to go a little bigger.

4) If I go from 4 to 5 ton, can I still use the same electrical and venting hookups?

5) Knowing this is a replacement not a new install, about how much should I expect to pay for labor?

Thanks!
 
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Old 08-04-19, 02:30 PM
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You're kind of all over....
You should be able to repair the unit .

Replacing the evaporator or condenser is not a DIY job. It requires refrigerant handling which requires an EPA certified tech. Sizing the unit is done by figuring out the heat load of the house using a manual J calculator.
 
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Old 08-05-19, 09:52 AM
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technically anyone can get an epa license and buy the tools, etc but it's not worth it.

electrical problems can be repaired by you, refrigeration related it's best to call someone out for.
 
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Old 08-05-19, 11:58 AM
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Okay, so not a DIY project for me.

I believe this is a 4 ton unit. How long do these units usually last? Mine has been in operation for 18 years, so I think I should just replace it and not even pay to have it checked out. Agreed?

Thanks
 
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Old 08-05-19, 12:13 PM
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I had my 2-ton unit replaced last summer. I'm collidge edjumicated, and I have a highly inflated opinion of my abilities, so I briefly pondered doing the job myself.

The folks who I hired for the job had the old unit out and the new one installed and were backing out of the driveway in 75 minutes. As I stood there and watched them work (and marveled that this was a job they probably could have done blind-folded), I realized that 75 minutes would have been just about enough time for me to figure out where to start. It probably would have taken me a week to figure out how to get rid of the old unit. As was, in an hour and a bit it was leaving my property as if by magic (with a little checkbook thrown in for good measure).

Plus I *think* the new unit only carried full warranty if it was professionally installed.
 
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Old 08-05-19, 12:30 PM
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Fred,
Thanks and good point about warranty and professional install.

Burning question right now is how long do these units typically last? (4 ton). Mine is 18 years! If I can rule out repairing it it's the difference between a free estimate to replace and a $100 estimate to repair, plus, it's hot out!

Thanks
 
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Old 08-05-19, 01:17 PM
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18 years is a good run. Depending on the problem now might be the time to throw the towel in.
My Rheem Classic X is 26 years old and still going strong. You just don't know.

As an aside...... you have an automatic warranty when you buy a new system. With most companies..... if that system is registered.... the equipment warranty is doubled. The installing company is supposed to register it but many don't. A homeowner can do it too.
 
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Old 08-05-19, 01:42 PM
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15 years is average life per ASHRAE
 
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Old 08-05-19, 02:56 PM
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My unit is going strong after 21 years (I do all maintenance on it so I've fixed a few minor things). If it had a major issue I would look into replacing. Your problem could be a simple fix which it could then last another 5 years. I think $100 to get more life out of it is a pretty good deal. Cap replacement is less than $20. Without knowing what is wrong with it, I don't think you can make an informed decision on whether to replace.

People on this forum have helped a multitude of people by walking them through a fix.

1) Is troubleshooting and fixing a central air unit something a typical amateur can handle?
A big YES depending upon the issue.

Start a new thread with what is it doing or not doing.....
 
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Old 08-06-19, 05:37 AM
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Thanks, I appreciate all the comments, but I think I'm just going to have it professionally replaced. I just have too much other stuff going on right now. Fact is, other than throwing a tarp over it in the winter (and I don't always do that), I haven't maintained it. Also, new units are considerably more efficient and there's something about the coolant being no longer available on older models or harder to get, etc.

Thanks for your help and advice.
 
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Old 08-06-19, 07:53 AM
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Your old unit is probably better quality than the stuff being produced today - it would real shame if u replace it and all it needs is a capacitor or something. (a capacitor is no more than $40)

18 years isn't really that old.
 
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Old 08-06-19, 08:48 AM
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My 2-ton unit was about 20 years old. Based on the age of this house, the previous unit must have lasted about the same, give or take a year or two.

I live in a one-horse town so all he old HVAC companies owe their existence to word-of-mouth advertising, which means they in general are known for the candor and honesty. The repairman who came to look at it initially told me that it was repairable but a 20-year-old unit with a few new parts isn't likely to provide an additional 10 years of trouble-free service. So I opted for new.

Compared to the same summer months two years ago, my electricity bill is running about 20% less than with the old unit. If I get that same 20% difference five months out of every year, the new unit will pay for itself in 24 years. So if it also lasts 20 years, I'll have recouped 83% of the purchase price.
 
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Old 08-06-19, 06:45 PM
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peterthebuilder: What's the calculation for how many ton you need? I've got a 4 ton now, but I'd like to go a little bigger
Easy and most accurate way to determine air condition load is to gather basic data on existing unit run time. Wire hour meter into AC compressor circuit. Find run time for x hours at y temperature. It is simple math to get handle on the AC load.

Because of significant addition of insulation, mine runs 8 hours/day on hot summer days.

In many buildings since AC was installed, added insulation and load reducing factors has reduced load.

On the other hand if AC is running constantly during hot times of day a bigger unit is needed. That is assuming there is no operational issues.

https://www.amazon.com/dp/B01NCEBOJJ...0-54597a712499

A rough, quick way to check current AC operation is with dual probe digital thermometer. If the difference in temperature at compressor lines is 20 degree F or more then its cooling. https://www.ebay.com/itm/6802-II-Dua....c100010.m2109
 
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Old 08-08-19, 06:19 PM
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On the other hand if AC is running constantly during hot times of day a bigger unit is needed. That is assuming there is no operational issues.
on the hottest days of the year with the windows in direct sunlight, continuous operation is normal.

Only if the temp drifts well above the setpoint running continuously when everything is in perfect shape is a unit undersized.

An older system is likely to have dirty coils, not be properly charged, have leaky ductwork reducing performance.

Increasing size can mean having to enlarge ducts so it should be a last resort.

best way to size is by doing a accurate heat loss/gain calc.

A rough, quick way to check current AC operation is with dual probe digital thermometer. If the difference in temperature at compressor lines is 20 degree F or more then its cooling. https://www.ebay.com/itm/6802-II-Dua....c100010.m2109
Depends on the humidity - moisture in the air reduces the difference. A 10 degree drop can be normal if the return air is very humid.

16 to 18 can be normal at 50% humidity.

If the airflow is low, the temperature difference can be normal despite a problem.
 
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Old 08-09-19, 05:56 AM
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I would first diagnose the unit and determine the outcome from there.
DO NOT blindly increase tonnage. Bigger equipment is not at all better. And you’d likely have to modify and/or replace ductwork to do so.
 
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Old 08-09-19, 11:01 AM
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My post #13 was how this DIYer deals with things. Since this forum does not allow mention of some common diagnostic tools it described an alternative way of gathering helpful data.

There are endless variables in residential AC systems and operating conditions. Interpretation of the data is an individual call.

While common practice is to size systems to run 100% of time at design conditions, capacity does decline over time and some might like comfort under extreme conditions. While design temp here is 98F it has gone to 105F +.
 
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Old 08-09-19, 03:53 PM
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Maintain the machine and capacity shouldn't decline, especially with today's scroll compressors without valves to fail.

Oversizing kills dehumidification and duct upgrades can be required.

In fairness, it's not necessarily bad to have a bit of surplus capacity in very dry climates.

When sizing, effective capacity needs to be considered at design conditions, rating is at 80f indoor, 95F outdoor. Actual capacity falls short of tonnage in very hot climates.
 
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Old 08-10-19, 04:51 PM
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Except on design condition days, conventional AC's and heating systems are over sized for lesser conditions.

Anyone who has designed systems to maintain specific temperature and humidity control has faced the challenge of variable load conditions.

Modern computer controlled AC systems with variable speed compressors, blowers and variable refrigerant flow (VRF) provide desired performance over a wide range of conditions. However, it is even more important to match them to max load, than "on-off" systems.
 
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Old 08-22-19, 06:31 AM
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I ended up replacing the Furnace as well as the AC. The furnace was at least 30 years old and has been giving me issues on an off for the last 4 years. Also, I upgraded to a thicker air filter and got a new humidifier. Furnace is stage 2. Having HE furnance and AC unit together helped increase SEER of the AC beyond what it would have been if I bought the same AC without upgrading the furnace.

Installers were a small local business. The duct sealing could have been a lot better and more precise. I had significant air blowing out of the seams, around the humidifier and were the condensation pipe existed the unit. I was able to get it all sealed with metal duct tape and chalking. Overall I was pretty happy with the install. I got three bids but this one was considerably lower than the other two, although the others sold Trane and American Standard, which to my understanding are essentially the same hardware rebranded. My guy sold me Lennex which Consumer reports rated highly but a little less than American Standard.

Anyway, thanks for all the good feedback. Here's the cost for those who might be interested.

Replace Furnace and Air Conditioning Units:
-Lennox Elite EL296UH07XE36B Two stage heat 96% efficient 70K BTU gas furnace with high efficiency fan
motor
-Lennox 13ACXN030-230 2.5 Ton 15 SEER air conditioner
-Lennox C35-36B indoor cased A coil
-Lennox Healthy Climate Mechanical air cleaner with MERV 11 filter
-Custom supply and return air plenum adapters
-Equipment pad, disconnect switch, line set, and wire whip for outdoor unit
-Remove old equipment and haul away
-All necesssary piping and wiring
Total Price Installed: $7,600.00

Provide and Install Lennox Healthy Climate Power Humidifier Add $500.00
Total Due For All Above Listed Equipment and Materials and Installation: $8,100.0
 
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Old 08-22-19, 06:42 AM
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I’m glad your happy, but don’t use consumer reports or other like sites to determine brand. They know nothing about HVAC or how to get a quality unit.
Brand name literally doesn’t matter. It’s how it was installed.
 
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Old 08-22-19, 02:00 PM
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roughneck7,

Huh? You statement sounds a bit absolute. Unless the furnaces are literally made by the same company and just rebranded, of course there can be differences in options and longevity. Seer ratings, efficiency ratings, whether or not it's paired with a high efficiency AC unit, stage 1 or stage 2, with or without passive filters and humidification, high speed variable fans.... etc. Good or bad installation certainly would be a factor too!

As for Consumer Reports, they aren't the bible, but they are about as unbiased as you can get, and I was only referring to their ratings on reliability according to statistics collected by people who actually own the units. Maybe the confusion was that you thought consumer reports was actually using and testing these models and drawing conclusions which I agree would be pretty hard to do especially when also making long term predictions about longevity.

For what it's worth...

Results in the following chart are gathered from Consumer Reportsí 2017 Fall Survey and 2018 Summer Survey of 21,770 central air conditioning systems, owned by members who purchased a new unit between 2007 and 2018.
Our predicted brand reliability ratings are based on a statistical model that estimates problem rates within the first 5 years of ownership, for central air conditioning systems that are not covered by an extended warranty or service contract. We also adjust for the median number of months of use per year. The median in our survey was 5 months per year. Higher ratings are indicative of better reliability. Brands receiving a red or orange rating cannot be recommended by CR at this time.

Our brand owner satisfaction ratings are based on the proportion of members who are extremely likely to recommend their central air conditioning system to friends and family.
Predicted Reliability
Trane
8 / 10
American Standard
7 / 10
Armstrong
7 / 10
Bryant
7 / 10
Carrier
7 / 10
Ducane
7 / 10
Lennox
7 / 10
Amana
6 / 10
Arcoaire
6 / 10
Day & Night
6 / 10
Goodman
6 / 10
Heil
6 / 10
Payne
6 / 10
Rheem
6 / 10
Ruud
6 / 10
Tempstar
6 / 10
Coleman
4 / 10
Frigidaire
4 / 10
Luxaire
4 / 10
Maytag
4 / 10
York
4 / 10
Source: Consumer Reports' 2017 Fall Survey and 2018 Summer Survey
Owner Satisfaction
American Standard
9 / 10
Bryant
9 / 10
Carrier
9 / 10
Lennox
9 / 10
Trane
9 / 10
Armstrong
7 / 10
Ducane
7 / 10
Rheem
7 / 10
Ruud
7 / 10
Amana
6 / 10
Arcoaire
6 / 10
Day & Night
6 / 10
Frigidaire
6 / 10
Heil
6 / 10
Maytag
6 / 10
Payne
6 / 10
Tempstar
6 / 10
Coleman
5 / 10
Goodman
5 / 10
Luxaire
5 / 10
York
5 / 10
Source: Consumer Reports' 2017 Fall Survey and 2018 Summer Survey
 
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Old 08-22-19, 02:15 PM
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Trane is first on that list.
I could show you two identical Trane models. One would be a constant problem child that is needing constant service. The other would be the definition of reliability.
The difference?
The installation.
How it was sized, selected, and installed. That is what consumer reports doesn’t take into account.
The truth is the installation is what will determine how well the unit will run. Not the name on the box.
And the different manufacturers, they use common parts anyway. So most of the guts of the equipment are sourced from the same manufacturer, and not the people that built the hvac unit in the first place.
So your Lennox, is likely to share parts with York, whom got last place on the list.
I’ll also add that most problems and issues that consumers deal with have a direct link back to the original installation.
Read more here, on why the name on the box is pretty worthless-

https://www.angieslist.com/articles/...vac-brands.htm
 
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Old 08-22-19, 04:58 PM
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i have serviced most of the brands listed and others not on the list and there is almost zero difference in the longivity and serviceability between them.
It's true that many of these units use exactly the same components and the biggest difference between them is the color, case style and price.

What sets them all apart is how they are installed.
There are some basic installation techniques that will make a unit last and unfortunately it takes time and knowlege to do so.
That 75 minute installation Fred described is a good example.
Good installation practice dictates that after the tubing is installed the system should be evacuated with a vacuum pump to a certain minimum using a micron guage.
An added bonus is that if the required micron level is achieved and holds the system can be certified as leak free..........How many a/c installers even own a micron guage!
It could take 75 minutes for that to happen but if the tubing has sat uncapped in a truck or it is a humid day could take a couple of hours.

You really need to shop for an installer.
The brand you choose is meaningless.
 
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Old 08-23-19, 04:03 AM
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Greg/Roughneck,

Okay guys, I think you made your point about the hardware with the understanding that there is still a difference between high and low efficiency, seer ratings, stage 1 vs stage 2, etc. (Thanks for the article, roughneck). This idea isn't unfamiliar to me. I worked in a hardware store for many years and I'm aware that a lot of stuff is literally made in by the same company and just rebranded. Garbage disposal units come to mind. As I recall InSinkErator pretty much makes all of them yet there are many many brands.

I'm not a pro and don't claim even a good layman's knowledge, but it really seems to me these units are pretty well self contained and it's mostly a matter of just hooking them up to power and the ducts. Is there a lot of additional tweaking involved?

What are some of the things to look for in a "good install"? I don't know if "micron level" was checked, but all tubing was replaced inlets and outlets with all new PVC venting to the outside to draw air in and out. If the system was not "evacuated with a vacuum pump" what kind of symptom/problem would I notice? A new acoil was installed. New pad for the AC unit. Condensate plump was installed and clearly functions well serving both the AC and humidifier. Can you give me a sense of what the "basic installation techniques" are?

Or, if you like, what are the red flags to look for in terms of a bad install?

The owner had the most experience, but the guy under him who did my job had 9 years. He and a helper were at my home about 8 hours doing the AC, furnace, and humidifier.

BTW, I know different regions of the country have different pricing, but do you think I paid too much or too little? I was quoted up to 12K for the same job. Assuming either of you are pros, can you give me an idea what you would have charged?
 

Last edited by petethebuilder; 08-23-19 at 05:24 AM.
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Old 08-23-19, 11:56 AM
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A quality job starts with sizing the equipment correctly via manual J and not replacing size for size. Many times the unit was improperly sized from the original builder. This may involve a room by room manual J compared with a manual D for duct design.
Manual S may be used for equipment selection.
A duct analysis should then be done to verify the duct can move the amount of air the equipment needs.
Then the install can begin. This includes purging with nitrogen while brazing. A nitrogen pressure test should be done followed by a deep evacuation using a micron gauge. Custom sheet metal will likely need made for transitions to keep airflow turbulence to a minimum.
Then after the installation is commissioning. Things like airflow and refrigerant charge are set. Amp draws and temperatures are taken. So is static pressure. Everything is checked and verified correct.
 
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Old 08-23-19, 01:35 PM
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roughneck,

Of the 3 quotes I had, only one walked the house and sized up the windows then entered some formula. All three came up with the same BTU recommendation for the furnace. I have been living here for 20 years without issue, so they pretty much replaced same with same. No one looked at the ducts or even asked serious questions about where they were located and which were returns and supplies, etc. If they had I could have told them precisely as I'd been through them all recently due to past projects. It wasn't an easy task to chart them!

I honestly don't know what they tested, but I know they ran tests after the AC and furnace were on for a bit. Everything seems fine for now. I guess I'll just have to wait an see.

Unless you guys tell me I need to worry or watch out for stuff, I'm not sure what else to do at this point. Just based on my experience so far everything seems fine. Maybe I got lucky and got a good installer. I didn't just go with him because he was cheapest. He really seemed to know his stuff, was very straightforward and I didn't at all get the feeling he was BSing me or overselling me on anything.

Say, I posted elsewhere about this, but I'll ask you while you're here. The whole house humidifier is really just an Aprilaire knock off with the water passing through the filter. I don't run it in the summer and leave it manually in the "off" position. Still, I notice cool air coming out of the front vents on the unit. Can I just block this off with foam or tape or something and then just open it back up again in the winter when I run the humidifier? I don't see any need to keep that part of my basement cool and it's like having a register vent half open.
 
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