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

What it means

The compressor is pulling more current than it should, and the system shut down to keep the motor from burning out.
Causes range from a dead start capacitor (cheapest, most common) to a refrigerant overcharge to a compressor that's mechanically failing.
Don't keep restarting it — get a technician on the phone before you try anything else.

Affected Models

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

Common Causes

Start or run capacitor failed — compressor can't reach running speed and draws high current trying
Compressor mechanically worn — internal friction forces it to work harder
Supply voltage too low — motor compensates by pulling more current
Refrigerant overcharge raising head pressure and the load on the compressor
Compressor winding insulation breaking down, partial short to ground

How to Fix It

Shut it down — thermostat off, breaker off.

D5 is the one error where you do NOT want to reset and try again.
Repeated startup attempts on an overcurrenting compressor are how cheap fixes become rebuilds.
Check whether the breaker tripped.

A tripped breaker plus D5 confirms the overcurrent was real and the breaker did its job.
Don't replace the breaker with a larger one — that 'fix' bypasses the safety that's protecting the compressor.
If you have a multimeter, check supply voltage at the outdoor unit.

Should be within 10% of the rated voltage (usually 208–240V).
Below 195V is enough to cause compressor overcurrent on its own — and it's a utility or wiring issue, not a unit issue.
If you're not comfortable with live-circuit measurements, skip this step.
Call an HVAC technician with the model and serial number ready.

They'll clamp-meter the compressor amperage, test the capacitors, check supply voltage, and read refrigerant pressures.
Most residential compressors carry a 5–10 year parts warranty — if it's still in that window, the part is likely covered (labour usually isn't).
Ask about the capacitors first.

Failed capacitors are by far the most common cause of D5, and a test takes 30 seconds.
$75–$200 fitted, vs. $1,500+ for a compressor — always rule out the cheap fix first.

When to Call a Professional

Get a technician before you do anything else.
Each restart on a failing compressor accelerates the damage — what could be a $150 capacitor today turns into a $2,000+ compressor replacement.
Capacitor: $100–300.
Compressor: $800–2,500+.

Frequently Asked Questions

What is a start capacitor and why does it matter?

It gives the compressor motor a kick of stored energy at startup, the way a person leaning on a stuck door uses their full weight to get it moving.
Without that kick, the motor strains to start, draws huge current the whole time, and the strain damages the windings over weeks or months.
Capacitors are $10–50 parts that should be tested annually as part of any HVAC service.

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

Most early compressor failures aren't really failures — they're installation problems showing up.
Bad refrigerant charge (over or under), undersized wiring, or operation outside the rated temperature range will stress a compressor enough to trigger D5 within a few years.
Check your warranty — most are 5 years on parts, longer with registration.

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

Past 10 years and the compressor itself is dying? Usually replace the whole system.
A new compressor runs 50–70% of a new unit, and the rest of the old system (coil, expansion valve, fan motor) is also aging.
Under 7 years with a known cause like a bad capacitor or charge issue? Repair makes sense.