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AC compressor replacement: what it costs and when to replace the system instead

Updated 23 October 2026 · SEO Dons Editorial

Why do commercial air conditioning compressors fail?

Manufacturers' fault tables show that a compressor code is rarely a verdict on the compressor. Mitsubishi Electric's service manual for its PUHZ-SHW outdoor units lists nine cases behind a compressor overcurrent code, from a closed stop valve and low supply voltage to loose compressor wiring, fan faults and short cycling. A defective compressor is the seventh. Daikin's VRV IV code list puts compressor lock and over-current next to an unbalanced inverter supply voltage.

Refrigerant loss and contamination are the causes with a legal side. The same Mitsubishi manual lists overheated compressor operation caused by a shortage of refrigerant behind its high discharge temperature code, and warns that dirt, dust or moisture entering the refrigerant cycle can cause deterioration of refrigerant oil or malfunction of the compressor. Daikin says R410A requires strict cautions to keep the system clean and dry. A leak left open, or a repair that lets moisture in, is a route to a failed compressor, and the refrigerant leaks guide sets out the repair duties. Age is the third factor, covered in the guide to how long commercial air conditioning lasts.

Restarts matter too. Daikin says its system waits five minutes before restarting to prevent overloading of the compressor motor. That delay is protection, not a fault, and a trip that keeps returning needs diagnosis rather than another reset.

How does an engineer decide it is the compressor?

Not by ear. The leakage-checking regulation lists the parameters analysed on a misbehaving system: pressure, temperature, compressor current, liquid levels and recharge volume. A compressor becomes the candidate once those readings, the fault codes and the cheaper causes above have been worked through.

Daikin asks anyone calling for an intervention to give the complete model name, the manufacturing number from the nameplate, the installation date and the symptoms. A quote should identify the part the same way. "Condenser" can mean the outdoor coil or the whole outdoor unit, so ask which, by model and serial number.

What goes into the cost of replacing a compressor?

This guide found no official source for compressor replacement prices, so it gives none. A figure on a web page is a contractor's own quote, and prices vary by system: a single split and a multi-compressor VRF outdoor unit are different jobs. What can be sourced is what a competent job involves, and each element should be a line on a written quote.

ElementWhy it is thereQuestion for the quote
DiagnosisReadings and codes must point to the compressor before it is replacedIs diagnosis priced apart from the repair?
Refrigerant recoveryGOV.UK says a technician with F-gas qualifications must recover F gas from equipmentWho recovers it, and where does the gas go?
The compressor and partsModel-specific, identified by model and manufacturing numberWhich part, and what warranty on part and labour?
Cleaning and drying the circuitMoisture and dirt harm the oil and the compressorHow is the circuit proved clean and dry?
Refrigerant to rechargeType and quantity added go in the recordsWhich refrigerant, and how many kilograms?
Testing and follow-upWhere the equipment is leak-checked, a leak repair needs a re-check by a certified person within one monthAre the leak test and follow-up visit included?
RecordsArticle 6 requires gas added and recovered, and the contractor's details, to be loggedWill the log be updated and a copy supplied?
Access and isolationElectrical work needs competent peopleDoes the price assume access equipment or out-of-hours work?

A written quote should itemise parts, refrigerant and labour so that two quotes can be compared line by line; the guide to comparing HVAC quotes shows how. Ask for the company's and engineer's F-gas certificate numbers too, and use the certificate check before work starts.

Can an R22 system have its compressor replaced?

The refrigerant rules often decide this. REFCOM says systems using HCFC refrigerants such as R22 had to address a ban that came into force on 1 January 2015. Article 5 of the retained ozone regulation prohibits placing controlled substances on the market and using them. The exceptions in Article 11 allowed reclaimed and recycled HCFCs for servicing existing equipment only "until 31 December 2014", and NetRegs says the use of recovered or reclaimed HCFCs to top up or service equipment has been banned since 1 January 2015.

Article 5 does not apply to controlled substances already in equipment, so charge already in a system is not caught. Adding R22, whether new, reclaimed or recycled, is. Whether a particular compressor job can be done without adding or returning gas is for the engineer to state in writing. If it cannot, the realistic route is the one on the air conditioning replacement page.

How do you decide between repair and replacement?

Five points do most of the work.

  1. Refrigerant. R22 is covered above. For other refrigerants, supply rules are changing; see the GB F-gas changes guide.
  2. Age and condition. Compare the unit's age with typical service lives and ask what else on the same system is near the end.
  3. Efficiency. Ask for the rated seasonal efficiency of the replacement against the nameplate rating of the existing unit; the SEER guide explains the metric.
  4. History. The F-gas log shows past leaks and gas added. Repeat failures on one circuit weigh towards replacement.
  5. Warranty. Daikin's VRV manuals record a warranty card completed by the dealer at installation and say maintenance must be done by an authorised installer or service agent. Check what any warranty requires before work starts.

How a repair and a replacement are treated for tax is a question for an accountant; the capital allowances guide covers the allowances side. Readers who want contractors to quote a repair or a replacement can send an enquiry through the site's form, and the commercial air conditioning repair page explains how faults are diagnosed.

Sources

Common questions

Can site staff keep resetting a compressor trip?

Daikin says some codes can be reset with the ON/OFF button, depending on level, and otherwise to ask the installer. The system also waits five minutes before restarting to protect the compressor motor. A trip that returns means the cause is still there, so report it with the code.

Does a small split need an F-gas engineer for a compressor change?

Yes. GOV.UK says individuals need a category 1 certificate for all activities, or a category 2 certificate to install, maintain, service and recover refrigerant from systems under 3 kg of F gas (6 kg if hermetically sealed). Staff without the qualification should not break into the refrigerant circuit.

What happens to the old refrigerant?

GOV.UK says recovered F gas, or the whole unit, goes through a registered waste carrier to a licensed waste facility. Recycled gas with a global warming potential above 2,500 can only be reused in equipment owned or operated by the company that owned the original system or carried out the recovery.

Does the F-gas log change after a compressor replacement?

Yes. Article 6 requires records of gas added and recovered, the identity and certificate number of the undertaking that did the work, and the dates and results of checks. Operators keep them for at least five years.

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