If you’ve ever had a refrigerator or AC unit fail in the middle of winter, or just after a cold night, you might be surprised to learn that the issue wasn’t the cooling system, but the cold itself. Many refrigeration and air conditioning systems come equipped with an overlooked but essential component: the compressor heater. But what does it do, and why is it so important in colder climates?
What Are Refrigeration and Air Conditioning Compressor Heaters Used For?
Compressor heaters are used to prevent refrigerant migration and liquid slugging in refrigeration and air conditioning systems. These heaters gently warm the compressor’s oil and internal components, especially during cold ambient temperatures. By doing so, they help maintain proper pressure levels and protect the compressor from damage during startup.
Why Cold Temperatures Pose a Risk to Compressors
According to the U.S. Department of Energy, cold ambient temperatures can cause refrigerant migration, leading to harmful liquid slugging during startup.
Refrigeration and air conditioning systems aren’t just vulnerable to heat—they can be equally affected by cold weather. During long periods of low ambient temperatures, refrigerant can migrate to the compressor and condense into a liquid. This creates several serious risks:
- Refrigerant Migration: When the system is off, refrigerant tends to flow toward the coldest part of the system, often the compressor. This causes a buildup of liquid refrigerant in the crankcase.
- Liquid Slugging: If the compressor starts while liquid refrigerant is present, it may draw in liquid instead of gas. This can cause internal damage, such as broken valves or bent rods.
- Oil Dilution: Cold refrigerant can mix with the compressor oil, weakening its lubrication properties and leading to premature wear.
Compressor heaters prevent these issues by maintaining a mild, steady temperature inside the compressor. This helps keep the refrigerant in vapor form and ensures the compressor is properly protected during startup.
How Compressor Heaters Work
Compressor heaters are simple but vital devices. Installed either around the compressor’s base (as a crankcase heater) or internally, they apply low-wattage heat to maintain the compressor’s internal temperature above the surrounding air. This gentle heat prevents refrigerant from condensing into a liquid and mixing with the oil inside the compressor.
There are two common types:
- Crankcase Heaters: These wrap around the base of the compressor and keep the crankcase oil warm.
- Internal Heaters: Built into the compressor, these perform the same function from within.
The heater is usually powered on continuously or controlled by a thermostat to activate when outdoor temperatures drop below a certain threshold.
A few winters ago, I had a customer call about their walk-in freezer shutting down intermittently every morning. It turned out the compressor was trying to start while flooded with liquid refrigerant—classic slugging. They didn’t have a crankcase heater installed. After adding one, the system ran smoothly through the rest of the season. That experience showed me just how critical a small, inexpensive heater can be to the health of a cooling system.
When and Where Compressor Heaters Are Typically Used
Compressor heaters are most commonly used in environments where ambient temperatures can drop below 50°F (10°C), especially in colder climates or during off-seasons when systems are idle. They are typically found in:
- Residential HVAC systems in colder regions, especially heat pumps installed outdoors.
- Commercial refrigeration units, including walk-in coolers and freezers.
- Industrial chillers and systems with seasonal operation cycles.
- Systems with long refrigerant line runs are more prone to refrigerant migration.
In these cases, the compressor heater acts as a preventative measure to avoid cold-start damage. Even in milder climates, many manufacturers now recommend or include crankcase heaters by default to ensure long-term reliability and warranty compliance.
Types of Compressor Heaters and Their Differences
Compressor heaters come in a few different styles, each suited for specific applications, installation preferences, or system designs. The most common types include:
Crankcase (Wraparound) Heaters
These are external band-style heaters that wrap around the base of the compressor. They are easy to install, especially as retrofits, and work by directly warming the crankcase area where refrigerant often settles. Most residential systems use this type.
Insertion Heaters (Internal)
These are installed inside the compressor during manufacturing. They provide direct internal heating to prevent refrigerant condensation. Insertion heaters are more common in commercial or industrial systems and cannot be added after the fact.
Strip and Blanket Heaters
These flat or flexible heaters are used when wraparound heaters aren’t practical due to compressor shape or space constraints. They’re secured to the surface using adhesive or clamps and offer more coverage for irregular components.
Each heater type has its pros and cons, but all serve the same critical function—preventing refrigerant-related damage caused by cold starts. Choosing the right type depends on system design, accessibility, and climate conditions.
Do All Systems Need Compressor Heaters?
Not all HVAC or refrigeration systems require compressor heaters, but in certain conditions, they’re absolutely essential. Systems that operate in consistently warm climates may never encounter issues caused by refrigerant migration or cold startups. However, the need increases when:
- The unit is installed outdoors in areas where temperatures drop below 50°F.
- The system has long refrigerant lines, increasing the chance of refrigerant settling in the compressor.
- The equipment experiences frequent shutdowns and restarts during cold weather.
- The system operates intermittently or seasonally (e.g., cabin AC or backup refrigeration).
Some modern systems include advanced controls and low ambient protection features, but even then, manufacturers often recommend compressor heaters as added insurance. For critical or high-value systems, skipping this small component could lead to expensive compressor failure and downtime.
Maintenance Tips and Common Issues With Compressor Heaters
Compressor heaters are generally low-maintenance, but neglecting them can lead to costly system damage. Here are a few key maintenance practices and potential issues to watch for:
1. Regular Electrical Testing
Check voltage and continuity to ensure the heater is operating. A failed heater can go unnoticed until compressor problems appear.
2. Visual Inspections
Look for physical damage to wraparound heaters—cracks, frayed wiring, or corrosion. Also ensure the heater remains snugly attached to the compressor base.
3. Thermostat or Control Check
Some heaters are controlled by ambient or crankcase temperature sensors. If the control circuit fails, the heater may not turn on when needed.
4. Listen for Unusual Compressor Behavior
Hard starts, knocking sounds, or system trips during cold weather could indicate the heater isn’t working and refrigerant has entered the crankcase.
5. Replace During Major Service
If you’re replacing a compressor or refrigerant lines, it’s smart to also replace or upgrade the heater. It’s inexpensive insurance for your new components.
Ignoring heater maintenance is often a hidden reason behind repeated compressor failures. A few simple checks each season can keep your system protected and running smoothly.
Final Thoughts
Though small and often overlooked, compressor heaters play a critical role in protecting refrigeration and air conditioning systems, especially in cold environments. By preventing refrigerant migration, oil dilution, and liquid slugging, they help ensure a smooth startup and extend the life of one of the most expensive components in the system.
Whether you’re managing a commercial freezer, maintaining a heat pump in a cold climate, or simply looking to avoid future breakdowns, installing and maintaining a compressor heater is a smart, preventative step. It’s a low-cost solution to a high-cost problem, and one that can save you serious time, money, and frustration down the line.
FAQs
Q1: Can a system run without a compressor heater?
Yes, but only in warm climates or controlled indoor environments. In cold conditions, skipping the heater risks refrigerant migration, liquid slugging, and compressor damage.
Q2: How long should a compressor heater stay on?
In most setups, the heater runs continuously or cycles based on a thermostat. It should remain active during off-cycles in cold temperatures to prevent refrigerant migration.
Q3: Are crankcase heaters energy efficient?
Yes. Most heaters operate at low wattage (typically between 30 to 100 watts), consuming minimal electricity compared to the cost of repairing or replacing a damaged compressor.
Q4: Can I install a compressor heater myself?
If you’re comfortable working with electrical components and follow safety precautions, external wraparound heaters are fairly easy to install. For internal heaters or systems under warranty, professional installation is recommended.
Q5: What happens if a compressor heater fails?
If the heater stops working in cold weather, liquid refrigerant may enter the compressor. This can lead to startup failure, damaged components, and complete system breakdown.
Q6: Is a compressor heater the same as a crankcase heater?
Yes. The term “crankcase heater” is commonly used, especially in HVAC systems. It refers to the same component, a heater designed to warm the compressor’s crankcase and prevent refrigerant issues.
