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Is Your HVAC Compressor Not Turning On? Here’s How to Fix It

How to Fix the HVAC Compressor That Won’t Turn On?

An HVAC refers to Heating, Ventilation, and Air Conditioning equipment, and all these devices require a compressor (just like a heart in the human body) for their effective functioning. It is quite common that we pinpoint the compressor whenever the HVAC equipment is not working.

It is quite common that the air compressor has many more chances to wear quicker than other parts of the equipment. If anything happens wrongly or the compressor won’t turn on properly, it results in the unit malfunctioning. It is a must to clear the mechanical problems restricting its turn-on and make it perform well to use the HVAC equipment effectively.

Here, in this article, we are providing some simple steps to determine what to do when the HVAC compressor is not working or turned on.

Before starting the main topic, here is a small introduction to the HVAC compressor.

HVAC Compressor 

Mostly the compressor is placed on the outdoor part of the HVAC unit. It compresses cool, low-pressure, and gaseous refrigerant, and then squeezed into a condenser to move as a vapor from the outdoor unit to the indoor unit. Thus, it absorbs the hot air through the vents for proper cooling of the room, as the heat travels from warm to cool areas.

For this, it is essential to maintain the compressor well and in proper working order. The compressors last for around 12 – 15 years long. Some signs let you know the compressor is not turning on or is broken. Use a special gauge or equipment to know the exact part of the HVAC unit like the AC is getting the problem.

Usually, the air compressor is made of various parts that are replaced separately, which means you can check, inspect and replace the particular problematic part/component rather than replace the overall compressor. Thus, it saves a lot of time and money while fixing small issues in the compressor.

Why Won’t the AC Compressor Work Yet the Condenser Fan Runs?

Most times, the compressor might stop working due to various reasons even when the condenser and blower fan runs by blowing warm air through the vents. If the compressor is not turned on properly, you need to take a look at some offenders and the ways to diagnose them.

1. Overheating & Auto-Shut Down for Safety

A compressor might get overheated when there is no adequate suction cooling or condenser cooling, as it raises both the temperature & pressure. It has to work hard, even run continuously without stopping, which makes it overheated and gets shut off easily. For instance, the working pressure of an air conditioner will range from 50 – 450 PSI and if the pressure goes above or below this range, the unit might cut off the power to the compressor automatically.

2. System Contamination (or) Dirty Filter

Even the dirty filters or system contaminants including air, acids, moisture, dirt, and other pollutants apart from the heat & pressure can be a reason for this problem. If the filters or condensers of the air conditioner unit get clogged due to the buildup of dirt & debris, then the evaporator coil gets frozen due to the lack of airflow transferring the coldness. Then the pressure gets dropped in the refrigerant and triggers the low-pressure switch (<50 PSI), resulting in the power cut off to the compressor. So, quickly change the dirty filters.

Apart from dirty filters, you have to check and inspect the condenser coil whether there is any buildup on the outside unit. It works as an insulator to remove the heat pulled in from the room. Hence the refrigerant pressure goes high and thereby the high-pressure switch (>450 PSI) of the unit triggers to cut off the power supply to the compressor.

3. Lack of Lubrication

Sometimes, oil contamination (oil leaking/oil pump failure/oil trapped in the suction line) might lead to the compressor’s failure. Remember that insufficient oil lubricant or excessive oil in the compressor are some of the main causes of this problem. You need to check the oil level in the compressor to end this issue.

4. Electrical Problems

In most of these cases, the unit gets power and the condenser fan runs yet the compressor doesn’t power on. Current or voltage fluctuations lead to overheating and failure. This results in the frequent tripping of the circuit breaker and might damage the overall unit. For this, you have to hire an HVAC professional to handle and set the problem perfectly.

5. Refrigerant Flood back

The amount of refrigerant plays a key role in the compressor’s working, as it should not be too low or too high. If the equipment sensors any wrong amount of refrigerant, then it simply triggers either low or high-pressure switches, and thus the compressor gets turned off immediately.

The liquid refrigerant return to the compressor cylinder without vaporizing completely in the evaporator due to improper settings, any leakage, or refrigerant under/overcharge. Thus, it damages the compressor with runaway pressure. Then call the technician to measure the pressure levels of the refrigerant and thereby add the precise quantity to run the unit properly.

6. Dead Compressors

If the compressor is dead completely, then you have to either replace the compressor or the entire unit. If the replacement cost is less than 50% of the new unit cost, then go with it, or else prefer to purchase the new unit.

What to do When the Compressor Won’t Turn On? and How to Fix it?

A malfunctioning HVAC compressor will let you stuck in the heat of the summer or in the cold of the winter. Since it consists of various components, the problem might occur when any of these components get failed. Inspect them thoroughly to check where the problem lies and replace/repair that particular component rather than replace the overall compressor or HVAC equipment.

Here is some troubleshooting to check and pinpoint the source of the problem, yet remember that most of these can be done by professionals/technicians.

1. Check Electrical Wiring and Power Supply 

Initially, check whether the unit is receiving a proper power supply or not when you find a compressor or heat pump is not turning on. This can be due to the tripped breaker (or) blown fuse. However, frequent starts and stops wreak compressor havoc and thereby the whole HVAC unit. Also, check the voltage using a multimeter along with examining all the wiring in the unit, particularly those connecting to the outlet.

2. Capacitors 

The capacitors help to start and run the compressor, blower motor, and outer fan by supplying the required power. Yet sometimes it stops turning on the compressor due to broken or faulty capacitors. Thus, it causes a humming sound from the system as an indication. Replacing a capacitor and testing the overall working condition of the unit is the only way to resolve this issue.

3. Start Relays 

As a part of cleaning and maintenance tasks, the technicians check and replace the start relay along with the capacitor. The starter relay transfers the power supply from the capacitor to the compressor. You have to turn off the unit if heard any weird sounds caused due to the compressor getting access from a non-functioning capacity. Then take out the old one and install a new start relay to make the compressor work well.

4. Terminal Connections 

It is essential to check whether the terminal connections are tight and in place. As we all know that loose connections lead to various problems, including the irregular working of the compressor. So, check the connections and set them properly.

5. Valves 

The problem arises due to a broken valve. As the refrigerant is a liquid form in the compressor inlet and if the valves are broken, then the compressor runs yet the unit doesn’t work effectively. All you need is to inspect and replace the broken valves to get rid of this issue.

6. Regular Maintenance 

Regular maintenance and repairs (if required) will not only prevent the chances of ending a faulty compressor but also enhances the working life of your unit. It is a must to clean the buildup of dirt, and debris in the filters, evaporators, and condenser coil might lead to overheating the compressor and also shutting down the entire unit. Since the compressor works hard and has to deal with regular wear, this can be even harder if the unit is not maintained properly.

7. Thermostat Settings 

The thermostat itself is a culprit in some cases, as it won’t tell the unit to start cooling/heating. They won’t allow the unit to cool as it wrongly measures the indoor temperature. It is due to the reason that the thermostat was placed wrongly or improper installation. Thus, the compressor won’t turn on. For this, you have to check the batteries and change them (or) check the device setting.

8. Winding Problems in the Motor 

The winding problems in the motor can be an issue for the compressor working, as most AC units have separate compressor motors sealed to make them durable and last longer. In that case, check the coils of wires in the motor and replace the motor if required. If the compressor motor isn’t sealed then you should compare the replacing or repairing cost and then take a wise decision. Apart from the winding problems caused by the power surges, you have to check the thermal switch that turns off the motor when it overheats.

9. Lock or Stuck of the Compressor 

A compressor usually draws more power to start working, which means the unit initially draws more power to operate. In this case, some compressors in the model get turned off/lock up/stop automatically (or) it draws a surge of electricity continuously that results in overheating and thereby lock up the compressor. To resolve this issue, you have to hire a technician to fix it and to make it work properly.

HVAC Compressor – Not Turn On FAQs

1. How much it costs to replace the AC compressor?

Ans: The compressor is the most important thing in the AC system and its replacement is quite expensive, as it depends on various things such as tonnage (ton – cooling capacity), compressor type, available features, and its brand.
The price of the AC compressor will range from $2000 – $5000 (excluding the installation cost). Most people prefer to replace the overall system rather than replace the compressor upon its failure. This happens mostly while the unit is 5+ years older to save the power or repair bills or impossible to fix the issue.

2. How to Prevent Breakdowns in the Future?

Ans: We all know that regular HVAC maintenance will make the unit work smoothly and efficiently. Also, it enhances the compressor’s long life.
However, dealing with compressor problems is quite difficult for those who don’t have any expertise. In most cases, you need to call an HVAC professional to diagnose the issue and make it run again. Regular wear and tear are one of the main problems resulting in the breakdown of this compressor.
Here are some basic steps (regular maintenance and on-time repairs) that help you to fix this issue.
* Make sure to perform cleaning of filters, condenser coils, and supply vents at regular intervals to prevent clogging, or blockage that might further damage the compressor.
* It is essential to set up annual maintenance with the help of technicians to keep the exact refrigerant levels, check leaks, and clean the condenser coil.
* Minimal wear and tear will not only help the unit safe but also reduces your power bills.
* Replace the overall unit if the compressor of the unit experiences frequent repairs, why because the repair cost will be more (in terms of professional hire and power bills) compared to the cost of a new unit.
* Regularly inspect the electric wiring for the tripped circuit breaker or a blown fuse.
* The checklist of the various things like operating pressure/temperature, voltage, proper suction superheat, oil level, and contact points.
* Whenever you detect a humming sound from the equipment, you need to check and replace the starter relays and capacitors.
* Most of these complex repairs consist of dangerous chemical leaks and safety hazards that have to be handled particularly by trained professionals.
* Since the HVAC units are used for seasonal purposes. Ensure to examine the HVAC unit in both cases – before & after use.


To conclude this topic, there are many reasons behind not turning on the HVAC compressor. We mentioned some of them and suggest you hire an HVAC technician or professional to check the compressor thoroughly, including its individual parts and components.

Replace or repair the particular part detected rather than changing the compressor. In case, if the compressor gets damaged or dead then replace the compressor rather than the overall unit to save a lot of time, effort, and money.

Feel free to share your queries or thoughts with us in the below comments section. We will help you to resolve those compressor-related issues.

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