DIY AC Repair – AC Lost Its Cool? Don’t Sweat It – Here’s How To Fix it

As an Amazon Associate we earn from qualifying purchases (more).

Fix Your Own AC

Murphy and his stupid law dictates that an air conditioner must always break down at the absolute worst time: right after the repair services close up shop for the weekend. And always in the dead heat of summer. Sure, many AC techs will come out on Sunday. But they’re never cheap, and now you have to pay their inconvenience premium. Or do you? Nope! There’s one simple repair – the most common of all AC failures – that you can perform yourself and save some cool bucks in the process. In this hot little DIY AC repair tutorial, we’ll show you how to repair your own AC (and how to do it safely)!

Hot Under The Collar (And Everywhere Else) – DIY AC Repair

Here’s the scenario: I’d just finished up the picnic table project and was sitting at the computer tweaking the part of the article where I was complaining about the Florida heat. Next thing I know, I start to realize it’s getting really hot in the house and the AC is blowing warm air. I checked the thermostat: 84°. Ugh, the cruel irony!

No cooling fan action.
It sounds like the unit is trying to run, but this fan isn’t coming on.

I replaced the filter not too long ago and the thermostat seems to be working. But then I hear it coming from out back (the back yard, not Australia): the faint telltale “click” followed by a sustained “hum”. The hum would last about 20 seconds then stop, only to repeat a minute or two later. So I went out to the heat pump and waited for the next “click-hum” cycle to start. Sure enough, it’s coming from the AC unit.

The click is the relay (contactor) doing its job. And the hum is the compressor. Those are normal sounds. What isn’t normal is the fact that the cooling fan isn’t running. Then, sensing there’s a problem, the unit gives up and tries again in a couple minutes. The fan that circulates air through the ductwork is working; there’s air blowing from the vents in the house. But it’s not happy air. It’s hot and miserable. And so am I.

Safety First – Playing With Hot Electricity Is Never Cool

Kill main power to the air conditioner.
Before doing anything else, go to your main breaker box and switch off the power to the AC unit.

Given the symptoms, I believe what we’re facing here is a bad motor run capacitor. It’s by far the most common heat pump failure and an easy fix that you can tackle yourself. But before going any farther, make sure you understand the dangers of poking around electrical circuitry. NEVER try to work on a live circuit. Doing so is not cool; it’s dumb and can kill you.

Switch off the secondary breaker.
Near the heat pump itself, there’s usually another breaker box. Switch that off as well. Most AC technicians only kill power at this breaker. We suggest also doing so at the main breaker in case your unit is some weird exception to the rule.

ALWAYS disconnect power to the unit before removing the cover. Make sure you understand how to use your test equipment to verify that there is no power or residual charge before touching any internal wiring or components.

diy ac repair
This conduit is where power from the breaker box feeds into the unit. After removing the access panel, check the wires coming out of there with a volt meter to make sure the power is deactivated.

Undertaking DIY AC repair successfully will make you the family hero, and ours! But we prefer our heroes alive. That way they can enjoy the fruits of a job done well (and safely) – and continue to enjoy the awesome content here at Home Fixated! So please, be careful. If you don’t feel comfortable tackling this job, hire a professional.

Open Sesame – Repairing Your Own AC Unit

Repair your own air conditioner.
Every air conditioning heat pump is different. Mine is a Payne (especially when it doesn’t work! *cue rimshot*). To remove the access panel, I had to also unscrew the top and lift this corner.

Remove the screws securing the access panel. In my case, I also had to lift the top (after pulling even more screws) to make room for the panel to swing open. Then I was able to lift the access panel off of the brackets at the bottom. Remove the access panel and set it aside.

DIY AC repair
Here’s what’s behind my access panel. Yours is likely to be set up a bit differently, but the basic procedure holds true for just about every unit out there.

Double Check That There Is No Power Going To The Unit!

Pointing to the main power lines.
The red arrows point to the main power lines. Depending on your unit, they may be located differently. These are the wires coming from the breaker panel. They should be black and white, but don’t count on it.
Making sure there is no power.
DIY AC repair requires playing it safe. Checking the main power lines to be sure they are NOT energized.

Trace the power lines coming in from the breaker box. Set your volt meter to read AC line voltage. (That’s “AC” as in “Alternating Current”, not to be confused with “AC” for “Air Conditioning”.) Set your meter to the proper voltage range and verify that there is indeed no power to the unit.

The power is off. That's good.
Zero volts AC at the main power supply shows that the breakers successfully cut power to the unit.

But don’t start grabbing at things quite yet!

Make Sure The Capacitor Is Discharged Before Going Any Further

Find the motor run capacitor.
Locate the motor run capacitor. It’s almost always an aluminum can with two or three terminals (or sets of terminals) on top. The red arrow is pointing to the capacitor in my unit.

Just because the unit isn’t powered doesn’t mean there aren’t vicious pixies waiting to bite you. The capacitor is a fairly low value (at a high voltage) but it’s still capable of storing a nasty charge!

Note that I will occasionally use the term “cap”, which is technical shorthand for “capacitor”. The two mean the same thing and can be used interchangeably.

AC motor run capacitor.
You will usually be able to see the entire body of the capacitor. In this unit, it actually sits in a hole in the chassis. So you can only see the top of it from above.

Locate the capacitor. Sometimes there will be two separate capacitors: one aluminum-bodied capacitor and another one, often with a black, plastic body. You want the aluminum one. It will usually be cylindrical, but some are more oval shaped.

DIY AC repair
Ducking down, you can see the rest of the capacitor – the focus of this (and many other) DIY AC Repair jobs.

Measure And Discharge The Capacitor Voltage – Safely Repair Your Own AC Unit

Make sure the capacitor is discharged.
This time, set your meter to check for DC voltage. First measure between each of the terminals (sorry that picture file corrupted). Then measure between each terminal and the chassis, just to be sure.

The motor run capacitor operates on alternating current power. But since the unit is powered down, if it is retaining a charge, it’s going to be a DC voltage. So set your volt meter to DC Volts and probe the terminals to make sure the cap is completely discharged. Measure between the common lead and the other(s).

With two-lead capacitors, put one test lead on one terminal and one on the other. With three-lead capacitors (like mine), just measure between each terminal and the other two, namely between “COM” and “HERM”, and “COM” and “FAN”.

If you find any voltage (even if it’s only a few volts), use a long screwdriver with an insulated handle to short the terminals together. If there was any voltage, it will spark; that’s OK. Actually, you may want to go ahead and short the terminals anyway, just in case. If you measured voltage before, double check to be sure it’s fully discharged now. Hang in there, you’re almost an DIY AC repair pro now!

Feeling Hot Under The Collar? Pop That Cap!

Fix your own AC unit!
After discharging the capacitor, make note of which wires go where then pull it out of circuit.

Carefully disconnect the capacitor. You may find it easier to use a pair of needle nosed pliers. Grab and pull at the connectors (don’t tug on the wires). But first, make a record of which wire goes where. On mine, each terminal has a different number of lugs, so I wrote that number and the wire color on the metal chassis with a permanent marker. I also took a close-up picture with my phone. Don’t rely on memory or you may be sorry.

Motor run capacitor.
Many capacitors will have the terminals labeled “COM” (common), “FAN” (cooling fan, the one that’s not working in this case) and “HERM” (hermetically sealed unit; the compressor). Mine are marked but very difficult to read.

You’ll find more often than not that the capacitor is fastened with a metal strap. In this case, however, it’s just sitting in a hole, held in place by gravity. I had to move another part out of the way to get enough clearance to lift it out of there.

Testing The Capacitor – The Moment Of Truth

Dual capacitor.
A three terminal capacitor is really two capacitors in one can. This one is a 45uf and a 5.0uf (both rated to 6% tolerance) sharing a common lead at one end (the “com” terminal).

You can sometimes tell a cap is bad just by looking at it. If the top is bulged out (domed) – or, even more obvious, blown open – there’s no need to test it; it’s definitely bad. If it looks “normal” (flat on top), you can tell for sure by testing it.

DIY ac repair
I have the black lead of my cap tester on the common (“COM”) terminal and the red lead on the one that goes to the compressor motor (“HERM”). But this is an AC cap, so polarity doesn’t really matter. The capacitance value is reading 43.5uf, which is within the rated 6% tolerance.

To test the capacitor, use a… wait for it… capacitor tester! What? You don’t own one? Cool your jets; it’s not the end of the world. If your AC is doing the same thing(s) as mine (you hear the relay click followed by a hum, the circulating fan is blowing air through the ductwork as it should but the heat pump cooling fan is NOT running), odds are, this is the problem.

Buying a new capacitor in this situation is a pretty safe bet. Not a sure bet, mind you. But a high probability proposition that – in my opinion – is well worth the gamble. Especially considering most replacements can be purchased online for under $20.

Bad capacitor!
Now I’m testing the fan motor side and, as you can see, it’s reading as an open circuit. As suspected, it’s a bad cap! That’s great news!

The Last Thing I Want Is A Super Hot Wife – Especially In Bed With Me

Oops! That came out wrong. First of all, a little damage control: my wife IS super hot! (Phew, that was close!) Self-preservation aside, neither she nor I want to have to sweat it out until Monday. It’s already way too warm in the house and we’re spoiled creatures of comfort. Gratuitous sweating isn’t our thing.

Replacement part.
Here’s the replacement capacitor. Be sure to get one with the same capacitance value(s). And the voltage rating (usually “370” or “440” followed by “VAC”) MUST be the same or higher. Never lower.

The local appliance parts dealers have already closed for the weekend and it’s too late for next day delivery through Walmart’s website. We also don’t have Amazon Prime. Both of those sources have the part I need for around $8-12, but one is estimating Tuesday delivery and the other is saying Thursday. Ain’t happenin’, Cap’n! Not on my watch.

Being resourceful, I turned to Facebook and posted a listing to about fifteen local buy/sell/trade groups asking if anyone had a capacitor I could get from them tonight or tomorrow morning. And voilà, within twenty minutes I got a response from an AC technician in the next town over! He was willing to sell me one off of his truck for $20 (WELL worth it). And I tossed him an extra $5 for being so awesome.

Helpful tip: To search online for a new capacitor, use terms like “ac capacitor 45+5 370VAC” or “ac capacitor 45/5 370V”. But substitute in the proper values for your capacitor.

But The New Capacitor Is Bigger – Don’t Lose Your Cool!

DIY AC repair
The physical size of my replacement cap is a little larger than the original. But that’s OK. As long as the values are correct, all is well. Remember that there are different values of capacitors used in different heat pumps. Be sure to match up with your old one.

There’s a chance that the replacement part you receive will be physically larger or smaller. As long as the values are correct (and the voltage rating is the same or higher), it will work. But you may have to alter the mounting strap (or hole, in my case) to accommodate the new dimensions.

Enlarging the mounting hole.
My capacitor sits in a hole. The new part is a bit larger in diameter so I had to pull the mounting plate and enlarge the hole. The curved side of a half round file works great for this. As you stroke the file forward, make a sideways sweeping motion to preserve the curve of the hole.

With a strap mount, you can usually bend the strap or re-drill the screw hole to tighten or loosen it. Just make sure it’s secure and don’t crush the body of the capacitor. Also, make sure the terminals can’t short against or come too close to anything else.

Ready to mount.
I compared the old and new capacitors to verify that the number of posts were the same for the same terminals (so that my wiring notations would be correct). Don’t assume the layout of your new part is the same as the old just because it looks similar. Always verify that you’re connecting the wires to the right terminals.

Bringing Back The BTU’s – Even Our Dog Is One Cool Cat!

Installing the new capacitor.
Make sure you have plenty of lighting and wire the new cap correctly.

By the time I got back home with the part for this DIY AC repair, it was already dark. But I didn’t care; I have an aversion to being miserable. I turned on some bright outdoor lighting, grabbed a flashlight and installed the new part. Well, after resizing the mounting hole.

Restoring power.
With the new part installed (and you’re sure everything is in its place and properly reconnected), turn the breaker back on.

After installing the new part, re-engage the breaker(s) and enjoy your sweet, cool air! Carefully reattach the access cover once you see that all is well.

That's what I like to see!
Spin, baby, spin! My wife and I were the happiest couple in all of central Florida!

Some units may take a few minutes to reactivate after power is restored. But once it kicks back on and you see that fan spinning, you’ll be the coolest DIY AC repair guy or gal around!

President Of Your Own Fan Club – Easy DIY AC Repair

This obviously isn’t going to fix every case of AC failure, though it is a surprisingly common problem. The capacitors just fail over time. Other times they blow out as result of a thunderstorm. But the good news is there’s a good chance that the next time your AC fails, you may be able to restore operation without waiting days for a technician to make it out. And for a lot less money. So don’t get all hot and bothered. Stay cool, be safe, and fix it yourself!

Nab a replacement capacitor for about $10-$20 at Amazon:

Buy Now - via Amazon

Photo of author

About Steve

Steve made his first woodworking project at age 9 (in 1982) and whittled his first wooden chain at 18. He was also a consumer electronics repair tech and shop owner for a little over 20 years, until his impending obsolescence became impossible to ignore. Since then, Steve has focused passionately on manipulating his wood... in his workshop. Don't judge him.

Subscribe to our newsletter

Get access to free prizes, product sneak-peeks, reviews, how-to's and much more!

More Info | Email Privacy

4 thoughts on “DIY AC Repair – AC Lost Its Cool? Don’t Sweat It – Here’s How To Fix it”

  1. Excellent instructions! I like all the safety measures you take. People often mistake my checking and rechecking as a sign that I’m unsure of what I’m doing. But that couldn’t be further from the truth. I feel very confident BECAUSE I have never had a big screw up, BECAUSE I check and recheck. :). And I also agree 100% with labeling / taking pics. Better to have it and not need it! I learned THAT lesson the hard way. 🙁

    • P. S. I had an ac tech clip the bleed resistor completely off my cap in an attempt to make the compressor fail sooner. It was a 23 yr old unit, so it wouldn’t be suspicious for it to fail, or so he thought. I believe the resisters are internal now, but this was an older style. I had personally soldered the resister on it a few weeks prior. I found the resistor clipped on the ground. Snip marks on both sides. The cap let out a loud pop and spark when I discharged it with the screwdriver. I wasn’t expecting it. The resistor is there to bleed the charge off within moments, so with it gone, it was fully charged. Moral of the story is you never know what could happen, so play it safe!


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.