HVAC Error Code D5 — What It Means & How to Fix It

What Does This Error Mean?

Error code D5 on most HVAC systems means the compressor is drawing more electrical current than it should. This overcurrent protection shuts the system down before the compressor motor burns out. D5 can be caused by a failing compressor, a low voltage power supply, a refrigerant charge imbalance, or a locked compressor due to a failed start capacitor. This error always requires professional diagnosis.

Affected Models

Mini-split air conditioners
Central air conditioners
Heat pumps
Commercial HVAC units
Variable speed systems

Common Causes

The compressor is mechanically failing — its internal parts are worn and it must work harder, drawing more current
A failed start or run capacitor means the compressor cannot start efficiently, causing it to draw a high startup current continuously
Low voltage from the electrical supply forces the compressor to draw higher current to maintain its workload
A refrigerant overcharge is causing excessive head pressure, forcing the compressor to work much harder than normal
The compressor winding insulation has broken down, causing partial short circuits that increase current draw

How to Fix It

Turn the system completely off at the thermostat and at the circuit breaker. Do not attempt a reset or restart until a technician has diagnosed the cause. Repeatedly restarting a compressor with an overcurrent condition accelerates its failure.

Unlike some HVAC errors where a reset is the right first step, D5 is one error where restarting before diagnosis can cause serious and expensive additional damage.
Check your electrical panel for any related circuit breakers that appear tripped. A D5 error accompanied by a tripped breaker confirms that the compressor drew enough current to trip the overcurrent protection. A breaker that repeatedly trips on the HVAC circuit needs immediate professional attention.

HVAC compressors run on dedicated 240V circuits with specific breaker ratings. A tripped breaker is a safety device — do not use a larger breaker to 'fix' this problem.
Check the supply voltage at the outdoor unit if you have a multimeter and are comfortable with electrical measurements. AC voltage to the outdoor unit should be within 10% of the unit's rated voltage (usually 208–240V). Significantly low voltage (below 195V) can cause compressor overcurrent.

Low voltage from the utility or a long, undersized wire run to the outdoor unit forces motors to draw more current to maintain power output. Voltage checks require a licensed electrician or HVAC technician.
Call an HVAC technician and describe the D5 error. The technician will measure compressor amperage draw with a clamp meter, test the start and run capacitors, measure supply voltage, and check refrigerant pressures. This gives a complete picture of why the compressor is overcurrenting.

Bring the system model and serial number to the call. If the compressor is still under warranty (typically 5 to 10 years on residential units), the replacement compressor may be covered — though labor usually is not.
Ask the technician about capacitor replacement as a first step if the diagnosis supports it. Failed capacitors are a very common cause of compressor overcurrent and cost far less than a compressor replacement. If the capacitor is bad, replacing it may fully resolve D5.

A capacitor test and replacement takes about 30 minutes and costs $75 to $200. It is always worth testing capacitors before assuming the compressor itself needs replacement.

When to Call a Professional

D5 is a serious error requiring an HVAC technician immediately. A failing compressor that continues to be started can burn out completely, turning a repairable situation into a very expensive replacement. Call a technician before attempting any resets. Expect $100–$300 for a capacitor replacement, or $800–$2,500+ if the compressor itself must be replaced.

Frequently Asked Questions

What is a start capacitor and why does it matter?

The start capacitor gives the compressor motor a powerful electrical boost during startup — similar to how a jet needs full thrust to take off, then can throttle back once airborne. Without a good start capacitor, the compressor struggles to start and draws high current for the entire startup period. Over time, this damages the compressor windings. Capacitors are inexpensive parts ($10 to $50) but critical to compressor health. They should be tested annually as part of routine HVAC maintenance.

My HVAC is only 3 years old. How can the compressor be failing?

Compressor issues on newer units are usually caused by installation problems rather than component failure. An incorrect refrigerant charge (either over or under), undersized electrical wiring, or repeated operation outside the unit's rated temperature range can stress a compressor enough to trigger D5 within a few years. Check whether the system is still under warranty — most manufacturers offer 5-year parts warranties and some offer longer compressor warranties with registration.

Is it worth repairing or should I replace the whole system?

If the compressor itself is failing on a system more than 10 years old, replacement of the entire unit is often more cost-effective than compressor replacement. A new compressor can cost 50 to 70% of a new system, and the rest of the old system components (condenser coil, expansion valve, fan motor) will continue aging. For systems under 7 to 8 years old with known root causes like a bad capacitor or refrigerant issue, repair is usually the right call. Get a written repair estimate and compare it to new system quotes before deciding.