“My AC compressor runs for a few minutes then shuts off? This is not normal. What is causing it? How can I fix it?”
Alright, let’s tackle this one. A lot of people ask us why does the AC compressor shut off after 2-3 minutes. We will explain the possible reasons why this keeps happening, and how you can fix it.
Now, here is the common red line for all of these AC compressor starts and stops within minutes:
- You turn on the AC unit. The compressor starts off quite normal.
- The indoor AC unit starts outputting cool air.
- Two to three minutes after the start, the AC compressor shuts off.
You are left wondering what to do now. Do you turn the AC unit back on and try it again? For people who tried this, you usually get the same result, right? The AC compressor shuts off after 2 to 3 minutes again.
Something is obviously not right. The key to understand here is that the AC compressor shuts off to protect itself. It’s a safety precaution; if it were to run on, the compressor itself or the AC unit as a whole could be in danger.
So, AC compressor shutting off after 2-3 minutes tells you something is wrong (and you need to fix it). The good part is that you don’t need to be worried if you have blown the compressor by switching the AC on (a few times in a row, most homeowners try this with no success).
Alright, there are 4 key culprits that are responsible for AC starting off great but shutting off within a few minutes. Here’s the shortlist (we will go into details further on):
- Compressor overheating. In most cases, the AC compressor shuts off after 2-3 minutes due to overheating. This spike in compressor operating temperature can be due to dusty outdoor coils, broken fan motor, lack of airflow, and so on.
- Low refrigerant levels. If you have an undetected refrigerant leak, the now low freon levels can cause the AC compressor to stop after a few minutes.
- Wiring or capacitor issues. This is less likely, but in some cases, we see that a broken capacitor, wrong wiring, or just a bad thermostat can cause this.
- Lack of airflow. All AC units require enough airflow for operation. If there is a lack of airflow (due to too restrictive or dirty air filters, blocked supply air ducts, etc.), the AC compressor starts overheating and it will shut off in 3-5 minutes.
Note: If it’s not any of these, it’s probably the TXV valve (this is a common HVAC joke; when everything else seems OK with the AC unit, it’s probably the TXV).
Let’s go through each of these clusters of problems one by one to check why your AC compressor is causing problems:
1. Compressor Overheating In 2-3 Minutes
The compressor has a neat kill switch: If it gets too hot, it will shut off. If the AC compressor shuts off 2-3 minutes after the start, it is most probably due to overheating.
Now, why is your AC compressor overheating and shutting off? Here are the main culprits:
- Dirty condenser coils. These outdoor coils have to emit heat. If there is dirt on them, they will not be able to emit a sufficient amount of heat. This will propagate to the compressor, creating high head pressure, overheating it, and shutting the compressor and the whole AC unit off. Make sure to clean and maintain these coils regularly.
- Busted outdoor fan motor. To emit heat, the outdoor fan provides the airflow that takes away the heat. If the fan in not rotating – usually due to a faulty fan motor – the airflow over the condenser coils is not being generated. The heat cannot be emitted, resulting in overheating the compressor. Check if the fan is rotating properly.
- Obstruction in the outdoor unit. The AC compressor is located in the outdoor unit. All kinds of things can come into the unit; grass, leaves, dirt, rats, and, yes, even snakes (every HVAC tech has a story to tell you about that). All of them can obstruct the fan, prevent it from rotating adequately, not producing enough airflow to cool the condenser coils. This can lead to compressor overheating. Check if you have any of this stuff in the outdoor AC unit, and clean it out.
Alright, that’s the basic. If it’s not direct overheating, it might be low freon levels:
2. Low Refrigerant Levels Causing Compressor Shut Off
There is only one way the low refrigerant levels happen:
You have a leak in the refrigerant lines.
This leak and the subsequent low freon levels can cause all sorts of problems, including the compressor shutting off.
Without enough refrigerant, the whole unit may get overheated. The AC compressor is usually the first to overheat, and the first thing to shut off. If you suspect that you have low refrigerant levels that is causing the AC compressor to shut off in 2-3 minutes, the best action plan is to call your HVAC guy.
Recharging the AC refrigerant lines is not a DIY job. In most states, you will need a license to do that. That’s why the only people who can help you out are professional licensed HVAC techs.
Another thing an HVAC tech can help you out with is also compressor shutting off quickly due to electrical issues:
3. Electrical Issues Shutting The Compressor Off
Now, given that the AC compressor starts OK, you may not think of electrical issues at first. If something was wrong with the wiring, the compressor wouldn’t even start, right? Well, yes and no.
Here are the possible electrical issues that will shut off the compressor within minutes:
- Faulty capacitor. The capacitor, located in the outdoor unit, has a 5 to 10-year lifespan. Compared to a 15 to 20-year lifespan of the AC unit, it is very likely you will have to change them 2x or even 3x during the AC lifespan. If you have a faulty capacitor or the capacitor is not in full contact all the time, the compressor may start but it will quickly shut off (usually in minutes).
- Electric surge. This is usually a voltage surge that knocks out the compressor. It can be a one-time thing, or you might have burned through your amp breaker. Start it again; if it shuts off again, check the amp breaker.
- Faulty wiring. Wiring problems are a rabbit hole of complexity. An HVAC tech should be called to recheck or redo the wiring.
- Faulty thermostat. The wiring problem can extend to the thermostat as well. If the thermostat gives the wrong signal to the AC compressor, it might shut it off prematurely.
All these wiring issues are complex and need to be handled by an HVAC tech. Now, for the following culprits for this quickly shutting off AC compressor, you can actually do something yourself:
4. Lack Of Airflow
For normal operation, the AC unit needs enough airflow (measured in CFMs). If we have fewer CFMs that our AC unit need, it can lead to overheating the AC compressor and shutting it off.
There are two main culprits for reduced airflow:
- Dirty air filters. Whenever something doesn’t work with the AC, the dirty air filters should be in your mind. If these filters are dirty (or too restrictive, like MERV 13 or higher filter), the airflow is restricted. AC not getting enough air is pretty much like a human not getting enough air; it will suffocate. If you see that the air filters are very dirty, change them and try turning the AC compressor on again.
- Blocked supply or return air vents. Homeowners move things around; couches, sofas, TVs, and so on. Make sure that you didn’t put a couch in front of the supply air vents (located low on the wall). These provide vital airflow to the air conditioner. If it is blocked, it will lead to decreased airflow and the result can be the AC compressor shutting off within 3-10 minutes.
This is the basic AC compressor troubleshooting. Once you figure out what is causing the AC compressor to shut off after a few minutes, you can do some things yourself (changing filters, pulling out the leaves, dead animals from the outdoor unit), but for most things, you will need an HVAC guy to help you out.
Hopefully, you now have a good grip on what is causing the AC compressor to shut off, and how to go about solving things.