Heat pump or air conditioner compressor: when is replacement still worthwhile?

Short answer: the compressor is the heart and the most expensive part of a heat pump or air conditioner, usually €450 to €1,500 for the part alone. Replacing it is also specialist work involving refrigerant, which may only be done by a certified refrigerant (F-gas) technician. For a unit that is ten years old or more, replacing the whole unit is often the wiser choice. Important: many fault messages that seem to point to the compressor are caused by something else.

What the compressor does

The compressor raises the pressure of the refrigerant, and with it the temperature. That is the principle by which a heat pump moves heat from outside to inside and an air conditioner does the reverse. It runs under high load, draws a lot of power and has to handle a current surge at every start. It is precisely those starts that cause wear: a system that switches on and off too often wears out faster than one that runs steadily for long periods.

Fault messages related to the compressor

Brand	Code	Message
Remeha	H06.06	Compressor lockout, high pressure
Remeha	H06.07	Compressor lockout, low pressure
Itho Daalderop	A1 21	Compressor starting current too high or temperature protection triggered
Haier	16	Refrigerant leak

Read such messages literally. "High pressure" usually means the system cannot get rid of its heat: dirty filters, a fouled condenser or too little flow in the heating circuit. "Low pressure", by contrast, points to too little refrigerant or a restricted evaporator. In both cases the compressor is the part that triggers the protection, not the part that is broken. If you replace the compressor, the problem will be back two months later.

What to have checked first

Four things, in this order. The air side: filters, the fins of the outdoor unit, enough free space around it. The water side on a heat pump: the dirt filter in the return, water pressure, flow. The refrigerant: has the charge been checked by weight and is there a leak? And the electrical side: start capacitor, inverter PCB and wiring. That last one in particular is often skipped, even though a faulty inverter PCB produces exactly the symptoms of a bad compressor. Such a PCB is available as a separate part, for example the Itho Daalderop compressor PCB HP-S 55 (05-00546, €301.95).

What a compressor costs

Part	Manufacturer number	Price
Vaillant compressor 5 kW	0020192778	€ 454.95
Vaillant compressor 8 kW	0020175852	€ 489.95
Viessmann compressor XHV025 1P	7856488	€ 1,475.95

All variants can be found under compressors. On top of that, the system has to be recovered, evacuated, refilled with the correct amount of refrigerant and tested. Expect half a day of specialist work on top of the part.

Repair or replace?

This is the honest trade-off. For a unit of three to seven years old with a demonstrably faulty compressor, replacement is often sensible, especially if the rest of the installation is in good condition and the parts are still under manufacturer's warranty. For a unit of ten years or older it is a different story: the cost of compressor plus labour plus refrigerant approaches that of a new unit, while a new unit is more efficient, uses a modern refrigerant and comes with a new warranty.

Always ask for the measurements on which the diagnosis is based: pressures on the high- and low-pressure sides, current draw and the weighed amount of refrigerant. A compressor is not condemned by ear.

Rules on refrigerant

Work on refrigerant circuits is reserved for a certified refrigerant (F-gas) technician. Refrigerant must not be vented but must be recovered and recorded. Instalpunt does not install; have a qualified local installer do the work. This also means that you can order a compressor yourself, but you cannot fit it yourself.

Is de compressor van een oudere airco kapot, dan loont vervangen meestal meer dan repareren; de modellen staan bij · .

Frequently asked questions

How long does a compressor last?

Ten to fifteen years in a well-balanced installation. Lots of short starts, an oversized unit or years of running with dirty filters shorten that considerably.

My outdoor unit starts and switches off again after a minute. Is the compressor broken?

Not necessarily. This pattern also fits a high-pressure safety cut-out triggered by poor heat dissipation, or a start-up problem in the electrical control. Have the pressures and current draw measured before anything is ordered.

Is a faulty compressor covered by the warranty?

Many manufacturers give a longer warranty period on the compressor than on the rest, but make annual servicing a condition. Keep your service reports; without those documents a warranty claim is difficult.

Can I use a compressor from another brand?

No. Compressor, refrigerant, expansion valve and controls are matched to each other. Always use the type the manufacturer specifies for that unit.