A commercial HVAC system that stops working correctly is more than an inconvenience — it is a direct financial loss. In a shop, restaurant or office, climate control affects the comfort of customers and employees, the preservation of products and, in many cases, compliance with workplace regulations.
Knowing the most common faults, their symptoms and their causes allows you to act quickly, distinguish what can be resolved with basic maintenance from what requires specialist intervention, and above all, prevent problems before they occur.
1. The system does not cool (or heat) sufficiently
Symptoms: the premises do not reach the set temperature. The equipment runs but fails to achieve the desired conditions.
Common causes:
- Blocked air filters, reducing air flow and heat exchange capacity.
- Refrigerant loss due to a leak in the refrigerant circuit.
- Dirty outdoor condenser coil, preventing proper heat dissipation.
- Equipment undersized for the actual heat load (especially after refurbishments or change of use).
Solution: start with filter and outdoor coil cleaning. If the problem persists, a technician needs to check the refrigerant charge and compressor performance.
2. The unit cycles on and off constantly (short cycling)
Symptoms: the compressor starts, runs for a few minutes and stops. The cycle repeats continuously.
Common causes:
- Refrigerant pressure out of range (high or low), triggering safety pressure switches.
- Outdoor condenser blocked by dirt or insufficient ventilation.
- Thermostat incorrectly positioned or faulty.
- Compressor with an internal electrical or mechanical fault.
Solution: check that the outdoor unit is not obstructed and that air flow is adequate. If short cycling continues, a technical diagnosis with gauges and pressure analysis is required.
3. Abnormal noise from the indoor or outdoor unit
Symptoms: vibrations, rattling, buzzing or whistling that were not present when the equipment was new.
Common causes:
- Worn fan bearings.
- Fan blades unbalanced or with accumulated dirt.
- Refrigerant pipes vibrating against the building structure.
- Compressor with mechanical wear.
Solution: a new noise should never be ignored. It could be as simple as tightening a bracket or as serious as a compressor about to seize. Early intervention prevents more costly failures.
4. Bad odour when the system starts
Symptoms: musty, mouldy or acidic smell when the system starts up, especially after periods of inactivity.
Common causes:
- Mould and bacteria accumulation on the evaporator and condensate tray.
- Blocked condensate tray with standing water.
- Filters left dirty for an extended period.
Solution: thorough cleaning of the evaporator, condensate tray and filter replacement. In severe cases, a fungicidal treatment of the air circuit may be necessary. This fault has implications for indoor air quality and occupant health.
5. Water leaks from the indoor unit
Symptoms: water dripping from the indoor unit, or damp patches appearing on the ceiling or nearby wall.
Common causes:
- Condensate drain blocked by dirt, algae or sediment.
- Cracked or poorly levelled condensate tray.
- Failed condensate pump (in installations without gravity drainage).
- Missing insulation on the refrigerant pipe, causing external condensation.
Solution: in most cases, cleaning or unblocking the drain resolves the problem. This is one of the operations included in any preventive maintenance plan.
6. The system consumes more energy than normal
Symptoms: the electricity bill increases with no change in usage or conditions.
Common causes:
- Dirty filters forcing the compressor to work harder to compensate for reduced air flow.
- Refrigerant leak: the system runs with a lower charge and takes longer to reach the target temperature.
- Loss of duct insulation, with treated air leaking to unconditioned spaces.
- Ageing compressor with progressively declining performance.
Solution: regular preventive maintenance is the best protection against excessive consumption. If the increase is sudden, a full technical review is advisable.
7. Temperature differences between zones
Symptoms: some areas of the premises are well-conditioned while others are not. Obvious thermal imbalance.
Common causes:
- Poorly balanced duct network: supply grilles closest to the unit receive more air than those further away.
- Dampers closed or misadjusted.
- Indoor units in a multi-split system with incorrect air flow settings.
- Unequal heat loads between zones (one zone with more windows, more equipment or higher occupancy).
Solution: balancing the duct network or reconfiguring diffuser air flow rates usually resolves the issue. In some cases, part of the installation may need resizing.
8. The remote control or thermostat does not respond
Symptoms: the unit does not respond to commands from the remote control or wall thermostat.
Common causes:
- Flat batteries in the remote control (the most frequent and easiest fix).
- Faulty temperature sensor in the thermostat.
- Problem with the indoor unit’s electronic control board.
- Electromagnetic interference with wireless controllers.
Solution: rule out simple causes first (batteries, system reset). If the problem persists, a control system diagnosis is required.
9. Ice formation on the outdoor unit
Symptoms: the outdoor unit coil becomes covered in frost or ice, especially in heating mode during cold months.
Common causes:
- Defrost cycle faulty or disabled.
- Insufficient refrigerant charge.
- Outdoor unit fan faulty or with inadequate air flow.
- Extremely low outdoor temperatures combined with high humidity.
Solution: if ice forms occasionally on cold days and clears with the automatic defrost cycle, it is normal. If it persists, the refrigerant charge and defrost cycle operation need checking.
10. Error codes on the display
Symptoms: the unit shows an alphanumeric error code and stops working or operates in degraded mode.
Common causes:
- Each manufacturer uses its own coding system. Errors can indicate anything from a disconnected temperature sensor to a serious compressor fault.
- The most frequent codes relate to abnormal pressures, high discharge temperatures and communication failures between units.
Solution: note the exact code and consult the technical service. Resetting the unit (disconnecting power for 30 seconds) may clear one-off errors, but if the code reappears, a technician’s intervention is essential.
Prevention: maintenance as an investment
The majority of these faults are preventable with a proper preventive maintenance programme. The basic operations — filter cleaning, drain inspection, coil cleaning, refrigerant charge verification — are straightforward and cost far less than an emergency repair or the premature replacement of a unit.
A maintenance contract with a specialist company ensures these operations are carried out on schedule, meets RITE requirements and enables early detection of problems that, caught in time, never become costly breakdowns.
When to repair and when to replace
As a general rule, if the cost of repair exceeds 40-50% of the price of an equivalent new unit, or if the equipment is more than 12-15 years old and uses refrigerants being phased out (such as R-410A or the already banned R-22), replacement is usually the most sensible option in the medium term.
At Acoval, we provide preventive and corrective maintenance for HVAC installations in commercial and industrial premises across Valencia and the Valencian Community. If your HVAC system is showing any of these symptoms or you want to implement a maintenance plan to prevent breakdowns, contact us and we will assess your installation.
