Central AC - DIY

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Last Updated: Monday, 25 May 2026 23:32
Published: Monday, 31 March 2025 04:14
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Central AC - DIY

Installing a Central AC:

This is NOT a DIY. It's always installed by a professional. There are videos on how to do it yourself, but you would be better installing a ductless minisplit (may be multiple of them) to achieve the same result. Minisplits are DIY and lot easy to replace.

 

 

Replacement of AC: AC replacement labor is pretty expensive at $4K per installation just in labor cost. It's definitely a DIY, but only for people who have already handled minisplit Installation and repair. Here's 2 part video explaining it:

Part 1 (Replacing outside condensor unit): https://www.youtube.com/watch?v=sR5wIbNrs7Y

Part 2 (Replacing inside Evaporator coil): https://www.youtube.com/watch?v=oIDSNBOpBKg

Part 3 (Brazing and Pressure test): https://www.youtube.com/watch?v=mUwIKPoBYSo

 

 

Repair and Maintenance:

 

MAINTENANCE:

Filters: Regular changing of filters is essential not only for the long term health of your AC, but also to lower your electric bills. AC work by pulling warm air in, and then cooling it. So, filters are placed wherever he warm air is pulled in, so that it gets cleaned up before it goes thru the blower and around the evaporator coil. It need to be checked and replaced at all such places. The airflow direction is mentioned on filter, and it needs to be put the right way (basically the arrow needs to be pointing towards the AC evaporator,i.e into the AC system). These filters come in various size, thickness and MERV ratings. Don't go for too high MERV rating (i.e > 9) as they will cause your AC to work harder. Also, filters with higher MERV ratings are more expensive. Choose the right size filter based on your current filter size. For thickness, we used to have only 1 inch thickfilters which needed to be replaced every 3 months. Nowa days (as of 2020), you'll find filters with thickness of 4 inch or 5 inch, which need to be replaced once a year. These are more convenient, but usually cost more than 4X the price of 1 inch thick filters, negating the convenience advantage. Also,they are harder on AC as they are thicker. You can always interchange thickness of filter as long as the space allows for thicker filter to go over there. Thin filters can always be used in place of thick filters, but not the other way round (i.e may not always be possible to replace thin filters with thick filters).

I go with 1 inch thick, MERV 5 or MERV 8 filters. These may be had for < $5 a piece. Assuming 3-4 such filters in your house, you've to plan for ~$60-$80 per year in filters. FilterBuy and Filtrete are 2 top brands, but their filters are 2X the price of Home Depot own brand (HDX) and Lowes own brand (ProjectSource). I bu these in house brands as they perform just as well at half the price. Below are links for these. HomeDepot, Lowes , Costco, Target, Walmart and local grocery chains are few places to buy these filters,  

 

 

TUNEUP:

A lot of companies want to do "tuneup" for your AC and heating system for $100's of dollars. Most of the time, they are not really finding or fixing issues, but actually trying to upsell on problems that don't exist. Home Depot and Lowes offer "AC tuneup" specials for low price of $10-$30 per AC unit. I've used them at $30/unit (total $60 for 2 AC units) and felt it was a total wastage of money. They measure AC freon pressure, check capacitor values, drain water thru the pipe and then try to upsell. You can check all these things yourself. Home Depot and Lowes, both use, ARS Resue Rooter as their HVAC contractor in my area. Their technicians didn't seem interested at all in tuning up anything, or even sharing the details of what they measured (stating that I won't understand these). I never got the report, even though I called them and asked them to send me the report.

AC tuneup deals:

 

DIY REPAIRS:

A lot of common problems with AC are easy to fix, and you don't have to sell your kidneys to pay someone to repair it.

Video showing top 4-5 issues with AC issues and repairs (Taddy digest) => https://www.youtube.com/watch?v=wThzFULXxN8

 

1. Freon Topoff: 

Most of the repair of Central AC is around Freon leaking, which is a very common issue. Some Freon leaking is OK, as you can just top off every couple of years, instead of trying to find the leak and fixing it. However, AC repair companies which come and top off Freon charge a lot of money, usually around $100/lb, while you can get freon for around $10-$20 per pound.

Here's a video detailing how to do it => https://www.youtube.com/watch?v=J1s4wxDBe24

One more excellent 30 min vid from AC Service Tech => https://www.youtube.com/watch?v=qpXZhTRPIXc

Look for High side and low side pressures to be inline with what it's supposed to be. For R410A, you want low side pressure to be around 120PSIG, while high side pressure to be around 250-300 PSIG. It depends a lot on ambient temps (both indoor and outdoor) though. You don't want to target a particular pressure, instead you target for SH (super heat) and SC (Sub cool) values. In above vid, you see that after some refill of freon, SH was 60-37=23F, which was too high. The guy kept adding freon, until SH was 57-47=10F, which was in theballpark as per the chart. 

Link => 

Freon leak detection: This is harder and requires more tools. I've explained it under "Minisplit" section. Look for leak detection by first topping off freon, and checking with "Refrigerant leak sensor". On top of that, you can put soapy water at places you suspect of leak. If the AC is showing < 50 PSI on the plow pressure line (meaning most of the refrigerant has leaked), then you can vacuum out the AC, and then add nitrogen gas to it and do leak detection again. This process is more involved for AC than Minisplit, as the leak can happen at many more places. In an AC, leak usually happens at the evaporator coil, which is usually enclosed and sealed, so it's not possible to get to it, unless you want to unseal the system. Even if you detect the leak in there, there's not much you can do except changing the evaporator coil.

Freon leak Repair: Once leak is confirmed, I believe it's no use to detect the point of leak. Instead go for leak fix, using this cheap repair method that I've shown in the minisplit section (by using leak saver UV dye with sealer). If leak sealer method doesn't work, then you might have to go for leak detection described above by ripping off the seal around evaporator coil, and hopefully leak is somewhere where it could be patched (very rare). Usually the whole evaporator coil has to be replaced, which is expensive. Both the evaporator coil and the labor to replace it is expensive. So, try this cheap repair method and hope that God is on your side !!

 

2. Capacitor Replacement:

A lot of time, your AC will just die (not start at all) on a hot summer day. The most common culprit is the Capacitor that's on the outside unit. It's a dual capacitor (2 capacitors in 1 pkg), and is just connected via wires. The capacitor is usually inside the covering to protect electrical connections, so you have to unscrew the little covering on the side of the unit to see the capacitor. You can measure the cap b/w the 3 terminals via multimeter. The multimeter should show open (or infinite resistance) is the capacitor is good. If it shows close to 0 resistance, that means there' s a short in the capacitor, and the capacitor needs to be replaced. Sometimes the capacitor is not out right shorted, but has a lower capacitance value than what it's supposed to have. That means it''s out of spec and will fail in some time. This can't be detected by a multimeter, but you can buy the more advanced meters which measure capacitance too. This will give you the proper capacitance reading. It's better to replace them if they are out of spec, instead of waiting for them to fail. You can buy these capacitors from Home Depot, Lowes, etc for $10 a piece. The only spec that needs to match is capacitance value listed. It's written in MFD (micro farad) or uF. There are 2 cap values mentioned, ad you need to match with the new one that you are going to replace with. You do NOT need to match the part name from the printing on the capacitor. If you can't read the Cap value, then you need to call the manufacturer of your AC and they'll give you the part number and the cap values. Ignore the part number, as you can buy any brand of cap from anywhere. If a HVAC contractor comes to fix this, he'll charge you $300-500 for replacing these capacitors. It's a 2 minute job and saves you $$$.

Capacitor replacement (DIY HVAC guy) => https://www.youtube.com/watch?v=FQisFmMtAis

The 3 terminals of Cap are: C (common), FAN (fan) and HERM(Hermetic compressor). So, the 2 cap formed are b/w C-FAN, and b/w C-HERM. If you measure cap values b/w these you will see the values. HERM cap (~50uF) is listed 1st on the pkg, and it's always lot higher than the FAN cap (~5uF) which is listed next (i.e HERM_CAP/FAN_CAP). These are the 2 motors in the outside unit => one that cools the condensor (the visible big fan that you see, which is not a very powerful motor) and the other is the compressor motor that does the job of compressing to increase the pressure of refrigerant. This motor has to be lot more powerful to be able to do the pressurizing job efficiently, hence the higher cap.

The colored wires that connect to Caps in my AC are: Red is common, Purple is Fan and Yellow is Herm. It may be same or different colors. Make a note of these colors and what they connect to, so that you connect them exactly as it was before.

Link with details => https://hvactrainingshop.com/dual-run-capacitor/

My 3.5 TON AC from Lennox (for downstairs) read 44.74uF(HERM), 10.06uF(FAN), while specs were 45uF(HERM), 10uF(FAN). So, both the caps were good as they were within 1% of Spec. Even then, I bough one to keep for spare from here (I just looked for MFD 45uF + 10uF MFD, it came with 5 yr warranty, and is less than 1/2 the price of one from Lennox) => https://www.amazon.com/gp/product/B0932QKL5L

Similarly for 2 Ton AC from Lennox (for upstairs) read 34.5uF(HERM), 4.44uF(FAN), while specs were 35uF(HERM), 5uF(FAN). So, Fan Cap was bad as it was outside 10% spec. Even though the AC is running fine, it's not advisa;e to run AC with Caps which are more than 10% outside of spec. So,, I bought one from same company => https://www.amazon.com/gp/product/B0932RGKCX

Each of them cost $15 for a total of $30. HVAC Tune up guy gave me a quote of $700 for replacing both. Now that's a ripoff :(