Orapi Asia

What to Do About a Rusty Air Conditioner

Rusty Residential Air Conditioning Units

Your air conditioner endures significant wear and tear throughout its lifespan. While modern units are designed to be highly durable and capable of withstanding harsh conditions, they still require regular maintenance to ensure optimal performance. Neglecting proper AC tune-ups and exposing your unit to high moisture levels can result in issues such as rust formation.

A rusty air conditioner not only looks visually unappealing but also exhibits poor functioning. A rusty air conditioner may struggle to cool or heat your home efficiently, leading to increased energy consumption and utility bills. Moreover, if the rust is left untreated, it can spread and corrode various components of your AC, ultimately resulting in expensive repairs or premature system failure.

To prevent rust on your air conditioner, it is important to understand its underlying causes and take appropriate preventive measures.

Rusty Air Conditioner Causes

air conditioner corrosion

The formation of rust occurs when metals, such as steel or iron, are exposed to oxygen and water over an extended period. Once rust begins to develop, it can rapidly spread and inflict damage on the affected metal surfaces. Various components of an air conditioner are susceptible to rust, including coils, air filters, drain pans, compressors, refrigerant lines, fan blades, and ductwork.

Below are several common causes that contribute to the occurrence of rust on air conditioners:

1. Excessive Moisture

Rust formation is primarily triggered by an excess of moisture, which can originate from various sources such as condensation, rain, or high humidity. Your air conditioner plays a role in managing moisture during its regular operations. For example, as the system draws warm air from your home for cooling, the moisture present in the air condenses on the evaporator coils and subsequently drips into the drain pan. This moisture accumulation is a normal part of your AC’s functioning and poses no immediate harm.

However, complications arise when excessive moisture persists and comes into prolonged contact with the components of your air conditioner. One common scenario occurs when the drain pan is obstructed, leading to water overflow and potential infiltration into the unit. In a coastal area, salty and humid air can introduce corrosive conditions for your outdoor unit. Moreover, if your outdoor unit is surrounded by vegetation or shrubbery, it may come into contact with water and harsh chemical fertilisers, further accelerating metal corrosion. Additionally, direct rainfall on your outdoor unit can expedite the rusting process.

2. Volatile Organic Compounds

Air fresheners, paints, and common household cleaners contain volatile organic compounds (VOCs). When present in indoor air, these compounds can easily enter your air conditioner as it draws in air for cooling purposes. Over time, these harmful compounds can cause corrosion in the copper refrigerant tubing, leading to refrigerant leakage.

3. Lack of Maintenance

Failure to properly maintain your air conditioner can lead to various issues for your AC unit. The air conditioner filter plays a crucial role in eliminating dust and other contaminants from the air. If you neglect cleaning the air filter for an extended period, it can accumulate moisture and debris, ultimately causing the development of rust. Additionally, dirty filters contribute to the corrosion of coils.

During the cooling process, your AC system extracts moisture from the indoor air collected in the drain pan. If you fail to clean the drain pan regularly, it can become blocked, resulting in water leakage inside your home from the indoor AC unit. This water backup inside the unit creates an ideal environment for rust to form.

Proper maintenance of the outdoor AC unit is also essential. Leaves, twigs, and other particles can accumulate in the condenser, affecting its performance. Moreover, these debris can obstruct the drain system, resulting in a rusty air conditioner.

4. Air Conditioner Aging

Over time, your air conditioner undergoes the natural ageing process, and rust formation is common. As your unit approaches its lifespan of 10-15 years, it is bound to experience degradation resulting from regular usage. Rusty air conditioner components may show symptoms such as reduced airflow, increased energy costs, and unusual noises. To prolong the average lifespan of your AC unit, consider the following eight maintenance practices.

Remove Rust From Your Air Conditioner Condenser

If you discover rust on your air conditioner at an early stage, you can take steps to remove it yourself. However, if the rust has spread to critical components, it is advisable to seek assistance from an HVAC professional immediately.

Below are the steps to fix rusty air conditioner outdoor units:

  1. Ensure your air conditioner circuit breaker is turned off. To confirm it is properly off, use a circuit tester.
  2. Using a screwdriver, remove the screws securing the side panel of the outdoor unit. Consult your air conditioner manual to locate the exact placement of the screws on your specific AC model.
  3. Lift the cover of the outdoor unit to access the condenser. The condenser will appear as a square or rectangular panel featuring coils and fins.
  4. To clean rust off the coils, utilise an AC coil cleaner. Apply the cleaner using a pump sprayer, starting at the top of the fins and working your way down until all areas are thoroughly wet. For a light cleaning, allow 5-10 minutes for the cleaner to take effect, then flush the coils with a water hose or, if available, use a pressure washer for a thorough rinse. For deeper cleaning, Dilute your acid coil cleaner with 5-10 parts of water and apply as above. Repeat if necessary for extremely dirty AC coils. 


NU-COIL 101 (f.k.a. COILBRITE-100) is a powerful non-acid coil renovator and re-conditioner. 
NU-COIL 101 quickly cuts through oily grime and industrial fallout deposits and allows air conditioning systems and units to operate at maximum efficiency. 

5. Employ a coil renovator to ensure optimal upkeep of the air conditioning system. Opt for a coil cleaning solution, suitable for both indoor and outdoor use.


COILTRON is a self-rinsing air-conditioning renovator for chiller and cooler coils. 
COILTRON utilises natural condensation to flush away robbing particles such as soil, grease, lint, and other accumulations. 

6. Use a condensate pan maintenance product to clean the unit.


SOLIDAIRE Pink (9108) is a New Generation of time-controlled dissolving Tablet Gel that cleans and controls the development of sludge, lint and slimy organic deposit accumulations in A/C condensate pans and lines. 
SOLIDAIRE Pink uniquely designed formula with alpha-B8® turns the tablet into a very slow gel release giving it a positive, long-lasting and aggressive cleaning action while controlling stale water odours. When used as a regular preventative maintenance treatment. 
  1. If the condensate pan’s drain line is clogged, use an air conditioner drain line cleaner to dissolve any organic obstructions upon contact. Allow 10-15 minutes for the chemical to dissolve the slime, then rinse with water.


CONSOLV III is a slime dissolver used in air conditioning condensate drain lines. 
CONSOLV III dissolves slime, lint, and other organic matter and opens condensate drain lines.

8. Since Consolv III is acidic, you can also use it to dissolve and protect rust from your air conditioning unit for the following reasons: 

a. Dissolving Rust

Acidic solutions can dissolve rust and other metal oxides. Rust is a form of iron oxide that forms when iron reacts with oxygen and water. The acidic product can help break down the rust, making removing and preventing further corrosion easier.

b. Passivation

Some acids can promote the formation of a protective layer on metal surfaces called “passivation.” This layer acts as a barrier against further corrosion, helping to protect the metal from future rusting.

9. Finally, reassemble the outdoor unit and resume normal functioning.

Prevent Rusty Air Conditioner Problems

To effectively prevent rust, it is crucial to prioritise proactive HVAC maintenance. By consistently cleaning and inspecting your unit, you can eliminate accumulated dirt or debris, thereby minimising the risk of accelerated rust formation.

Clean AC Filters

Clean your AC filters once every two weeks. If you don’t remember to clean them frequently, you can use smart devices such as smart thermostats or smart AC controllers compatible with mini-split, window and portable ACs. These innovative gadgets monitor the cleanliness of your filters and send timely alerts to your smartphone, reminding you when it’s time for the next cleaning.

AC Coil Cleaning

Every two months, it is recommended to perform AC coil cleaning. This can be accomplished using various methods, such as commercially available cleaners, compressed air, and heavy-duty coil cleaners. 

Inspect Outdoor Unit

Periodically inspect your outdoor unit to identify any accumulation of leaves or debris on the top or sides. Additionally, maintain a routine of cleaning the surrounding area and trimming vegetation near the unit.

Maintain Clean Drain Lines

Over time, excessive moisture can cause blockages in the drain pan, which can contribute to the development of rust. To prevent this, utilise a long wire brush to thoroughly scrub the drain line. Additionally, consider pouring bleach down the condensate drain line every six months to effectively clean and clear any accumulated debris.

Protective Coating

If you reside in a coastal area with elevated moisture levels, it is advisable to opt for units that feature a rust-resistant coating. This coating is an effective barrier against rust formation, helping prolong your HVAC system’s lifespan in such environments.

Can I clean my air conditioner coils myself

Yearly Professional Inspection

HVAC experts will comprehensively evaluate your system to guarantee optimal performance. Through annual check-ups, they will ensure that filters are debris-free, coils are cleaned, and the condenser is operating efficiently. This inspection also includes measures to identify and halt the progression of rust. The professionals will endeavour to determine the root cause of rust and implement preventive measures to avoid its recurrence in the future.

Use a Protective Cover

When your air conditioner is not in use, consider utilising a waterproof cover specifically designed for air conditioners. This cover protects against excessive moisture in the surrounding air, effectively preventing rust formation on your unit.

Conclusion: Rusty Air Conditioner

A rusty air conditioner are not only less efficient but also more likely to breakdown. High moisture levels and inadequate maintenance are commonly responsible for rust formation. Thankfully, you can prevent most instances of rust by prioritising regular AC tune-ups. Regularly cleaning the filters and coils, clearing debris from the unit’s exterior, and scheduling professional inspections at least once a year are crucial steps. By following these practices, you can ensure your air conditioner remains in excellent condition for years, free from unsightly rust patches.

In this chart, you able to identify the specific corrosion you may be encountering and determine the appropriate next steps for treating the corroded surfaces.
Pure Chemical Corrosion Types of Alloy Reaction Chart Type 2

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Pure Chemical Corrosion Types of Alloy Reaction Chart Type 2

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The chart will aid in accurately identifying the specific corrosion you may be encountering.