When the compressor goes: diagnosis, cost and the replace decision
Contents (7)
« Compressor gaya hai » is the most expensive sentence a technician can say in an Indian summer, and it is said far more often than it is true. The compressor is the one component whose failure genuinely reframes the decision from a repair into a purchase — which is exactly why it deserves a second opinion before you accept the verdict. A large share of machines condemned in May are running again the same week after a capacitor, a relay, a control board or a leak repair.
What the compressor is, and which type you have
The compressor is the pump at the heart of the refrigeration cycle: it raises the pressure of the refrigerant vapour so that it can give up heat outdoors and turn back into liquid. It sits inside the sealed dome in the outdoor unit, motor and pump welded together in the same refrigerant atmosphere — which is why a burnt motor winding contaminates the whole circuit, and why the repair is never just a swap.
| Type | Where you meet it in India | Notes |
|---|---|---|
| Reciprocating | Older window units, some small commercial | Piston-and-valve; noisier; tolerant and repairable at circuit level |
| Rotary | Most fixed-speed splits and modern window ACs | Compact and quiet; the standard Indian domestic compressor |
| Twin-rotary / variable speed | Inverter splits | Driven by the outdoor PCB; a failure here is often the board, not the pump |
| Scroll | Ducted, cassette and light commercial | Efficient, expensive, replaced rather than repaired |
The distinction matters when a diagnosis is offered. On an inverter machine the compressor cannot start without a working inverter board, and a failing board produces symptoms that look identical to a seized pump from outside the unit — the reason our guide to how inverter ACs work is worth reading before agreeing to a quotation.
The symptoms, and what each one really means
- The outdoor unit hums, then trips after a few seconds. The motor is trying to start against a load it cannot overcome. On a fixed-speed machine this is a start or run capacitor at least as often as a seized compressor — a cheap part, and the first thing a competent technician should measure.
- The MCB trips the moment the outdoor unit engages. Could be a shorted winding; could equally be the circuit itself. If a light circuit is feeding the AC, the guide to the wiring and MCB behind an AC covers what a correct supply looks like before you blame the machine.
- The indoor fan blows, air is not cold, the outdoor fan spins but the unit is silent underneath. The compressor is not running. Cause could be the capacitor, the contactor, the thermistor, the board, or a protection cut-out on low refrigerant.
- The unit cools, then stops after twenty minutes and restarts later. That is usually the overload protector doing its job — most often because the condenser is choked with dust and head pressure is climbing at 45 °C, not because the pump is dying.
- A loud metallic knocking or a marked new vibration. Internal mechanical damage. This one is genuinely bad news.
Before accepting a compressor verdict, ask three questions: has the capacitor been measured, has the pressure been read on gauges, and has the supply voltage been checked at the outdoor terminals while the machine tries to start. A technician who cannot answer those has not diagnosed anything. Our guide to an AC that has stopped cooling sets out the same checks in the order they should happen.
Why compressors fail early in India
Compressors are built to run for a decade or more. When one dies at year four, something in the installation or the environment killed it, and identifying which one matters — otherwise the replacement follows the same path.
- Supply voltage. Sustained low voltage forces higher current for the same work, and heat is what destroys windings. In areas with weak evening supply, this is the leading cause, and the case for the protection described in our guide to stabilisers and stabiliser-free ranges.
- A dirty condenser. A coil packed with dust cannot reject heat; discharge pressure and discharge temperature climb; the compressor cooks slowly. This is entirely preventable with a rinse twice a season.
- Running low on refrigerant. Refrigerant also carries oil around the circuit and cools the motor windings. A machine running for weeks on a slow leak is a machine running hot and under-lubricated — which is why the practice criticised in our guide to annual gas top-ups is not merely wasteful but actively destructive.
- Short cycling. Every start is the harshest moment in the compressor’s life. An oversized machine in a small bedroom starts and stops all night; sizing it correctly with our tonnage guide is a longevity decision as much as a comfort one.
- Moisture and contamination. A circuit opened and closed without proper evacuation traps moisture, which forms acids with the oil and eats the windings from inside. Sloppy service work kills compressors years later.
The warranty sticker, read properly
Indian manufacturers commonly advertise a long compressor warranty alongside a much shorter comprehensive one. Read the two as separate things: the long cover is typically for the part alone. Labour, refrigerant, the filter drier, flushing the circuit and transport are usually billed to you, and on a compressor job those items are a substantial share of the total. A warranty claim also generally requires proof of purchase and evidence the machine was installed and serviced properly — the ground on which claims are actually refused, as our guide to AC warranties in India details. Get the quotation itemised before authorising work, not after.
The arithmetic of replacing a compressor
A compressor replacement is not one price but a stack of them, and quotations diverge because different shops include different lines:
- The compressor itself — OEM or aftermarket, and the difference is not trivial.
- A new filter drier, mandatory on any circuit that has been opened.
- Full evacuation and a fresh refrigerant charge.
- Labour, brazing, and often transport of the outdoor unit to a workshop.
- Where the old compressor burnt out, flushing the circuit — skipping this is the classic reason a replacement fails within a year.
Prices vary by city, tonnage and refrigerant, and anyone quoting a national figure is guessing; what is stable is the ratio. Out of warranty, a full compressor job on a domestic split typically lands somewhere around a third to a half of what a comparable new machine costs. That ratio is the decision rule.
| Situation | Sensible call |
|---|---|
| Under compressor warranty, machine under 6 years, efficient | Replace the compressor; negotiate the labour and gas line |
| Out of warranty, 8+ years old, fixed-speed, low star rating | Replace the machine — the efficiency gap repays part of the difference |
| Runs on R-22 | Replace the machine; servicing supply is on a declining schedule |
| Second major failure on the same unit | Replace the machine |
| Cause was voltage or a dirty coil, and it is unfixed | Fix the cause first, whatever you decide about the machine |
The refrigerant line deserves emphasis. Manufacture of HCFC-22 room air conditioners has been discontinued in India under the country’s HCFC Phase-out Management Plan, and supply for servicing is on a declining path toward the Montreal Protocol phase-out date, with only a limited servicing tail beyond it. Spending heavily on a major repair to an R-22 machine buys you an asset with a shrinking service ecosystem — the background is in our guide to refrigerants in Indian ACs. On the other side of the ledger, a decade-old three-star fixed-speed unit is materially thirstier than a current five-star inverter of the same tonnage, and in a heavy-use household that gap is a real annual sum rather than a rounding error.
Making the next compressor last
Whatever you decide, the protective measures are the same and none of them are expensive: keep the condenser clean, give the machine a stable supply, size it correctly, fix leaks rather than topping up, and insist that any technician who opens the circuit evacuates it properly. The seasonal routine in our maintenance guide for Indian conditions covers most of it, and it costs a fraction of the repair it prevents.
Frequently asked questions
How do I know whether it is really the compressor and not the capacitor?
A failing capacitor produces a hum and a trip on start, exactly like a seized compressor, but it is measurable in a minute with a meter and costs a small fraction of a compressor job. Insist on that measurement, and on a voltage reading at the outdoor terminals, before any large quotation is authorised.
Is replacing the compressor worth it on an old AC?
Out of warranty and past roughly eight years, usually not. The job typically costs a third to a half of a new machine, the rest of the unit is the same age as the failed part, and a current inverter model of the same tonnage will use noticeably less electricity every month it runs.
My compressor is under warranty — will the repair be free?
Rarely fully free. The long warranty normally covers the part, while gas, labour, the drier and transport are billed separately, and those lines add up to a meaningful bill. Ask for an itemised estimate before the work starts.
Can low refrigerant damage the compressor?
Yes, and this is under-appreciated. Refrigerant carries oil through the circuit and cools the motor windings; running for weeks on a slow leak means running hot and under-lubricated. Repair the leak rather than scheduling an annual top-up.
Does a stabiliser actually protect the compressor?
Where the supply genuinely sags or spikes, yes — sustained low voltage raises current and heat, which is what kills windings. Many current inverter models have a wide stabiliser-free operating range; the question is whether your local supply stays inside it, not what the carton claims.
Sources
Read next
- The inverter PCB: the other expensive failure in an Indian split AC
- Buying an AC on EMI: what « no cost » actually costs
- Portable air conditioners in India: what the wheels really cost you
- What an air cooler really costs to run: electricity and water
- AC fires and “blasts”: what actually burns, and how to prevent it