Air-con and heating: a luxury that became a necessity
Do you remember the days when air-conditioning in a car was a luxury option? Today it is a standard without which we cannot imagine driving. The same goes for heating, which has actually always been standard equipment but we took it for granted while it worked.
Then summer comes and the air-con does not cool. Or winter comes and the heating blows cold air. Or the blower only runs on the highest speed. Or you hear strange noises from under the bonnet when you switch on the air-con. All of these are signs that something in the HVAC system (Heating, Ventilation, and Air Conditioning) needs a repair or replacement.
And when you see the prices of new parts for the air-con system, especially compressors, you wish you could go back to the days when we just rolled down the window. But there is no need to worry, used parts for the air-con system and heating are one of the best categories for saving.
How the air-conditioning in a car works
Air-conditioning in a car works on the same principle as the fridge in your kitchen, only adapted to operate in a vehicle. Here is a simplified explanation:
- The compressor compresses the refrigerant (gas) under high pressure, which heats the gas
- The hot gas passes through the condenser (placed in front of the engine radiator) where it cools and turns into a liquid
- The liquid passes through the expansion valve where it suddenly expands and cools
- The cold liquid passes through the evaporator (placed inside the cabin) where it absorbs heat from the cabin air and cools it
- The gas returns to the compressor and the cycle repeats
In this system there are many electrical and electronic components: the compressor's electromagnetic clutch, pressure sensors, the evaporator blower with a resistor for speed control, the climate control unit, switches, servo motors for directing air ... Each of those parts can fail and each can be found used.
Heating system: simpler but not without trouble
Heating in a car works by routing the engine coolant (heated by the engine running) through a small radiator inside the cabin called the heater core. A blower pushes air through the heater core and warm air enters the cabin.
The electrical components of the heating system include:
- Cabin blower (blower motor) - pushes air into the cabin, the same blower is used for both air-con and heating
- Blower resistor - regulates the blower speed, one of the most common faults
- Flap servo motors - direct the air to the feet, chest, windscreen
- Temperature switch/regulator - the control on the dashboard
- Cabin temperature sensor - on automatic climate, measures the temperature in the cabin
- Electric heater (PTC element) - on diesels and some petrols, an extra electric heater that warms the air until the engine warms up
The most common faults and used replacement parts
Air-con compressor
The compressor is the heart of the air-con system and at the same time the most expensive part to replace. A new original compressor costs 300 to 800 euros, plus refrigerant, oil and fitting. The total easily passes 700 euros.
A used compressor costs 80 to 250 euros. But buying a used compressor calls for care:
- Check that the clutch works - the electromagnetic clutch on the front of the compressor must engage and disengage when it gets a signal. You can test it by connecting it to 12V.
- Turn the compressor by hand - it must turn smoothly, without catching or grinding. If it is jammed or hard to turn, the bearings or the internal mechanism are damaged.
- Check the seals - refrigerant leaks are a common problem. Look around the joints and on the compressor body for oily stains (refrigerant oil mixes with the refrigerant and leaves visible traces at leak points).
- Ask about the reason for replacement - if the compressor was removed because the air-con stopped cooling, you need to know whether the problem was in the compressor or somewhere else in the system.
Important note: when fitting a used compressor, the system has to be flushed, filled with new refrigerant and oil, and tested for leaks. That is a job for a workshop with the right equipment.
Cabin blower resistor
This is probably the most common fault tied to heating and air-con. The symptom is classic: the blower runs only on the highest speed, and the other speeds do not work. That is because the resistor has burned out and the only remaining speed is the one that bypasses the resistor (full speed).
A new resistor costs 15 to 60 euros, and a used one 5 to 20 euros. Given the low price of a new one, this is one of those parts where the saving on used in absolute numbers is not huge. But if you have an older car and every saving helps, a used resistor is perfectly fine.
The swap is usually simple: the resistor sits near the blower, usually under the dashboard on the passenger side. Two screws and a connector, a 15-minute job.
Cabin blower (blower motor)
When the blower stops working completely (no speed at all), the problem is usually in the blower motor itself or in the fuse/relay. The blower motor can burn out, the brushes can wear down, or the bearings can seize.
The symptom of worn bearings is a characteristic squealing or whining when the blower starts, especially on lower speeds. Over time it gets louder and the blower eventually stops.
A new blower motor costs 50 to 200 euros, used 20 to 70 euros. The swap calls for removing part of the dashboard or the cover under the windscreen, depending on the car. The job takes part of a workshop shift for an experienced mechanic.
Flap servo motors
Automatic climate systems use servo motors to drive the flaps that direct the air. When a servo motor fails, the air only comes out of one place (e.g. only at the feet or only at the windscreen), or the temperature does not match the settings.
A common symptom is clicking or grinding from the dashboard when you switch on the air-con or change the temperature. That is the servo motor trying to move the flap but unable to because its gears are worn or the motor has burned out.
A new servo motor costs 40 to 150 euros, used 15 to 50 euros. Access is usually awkward because they sit deep inside the dashboard, so fitting can be long and expensive.
Climate control unit
The climate control unit (climate control module) is the electronic brain of the system. It receives data from temperature sensors, the sun sensor and the user's settings, and uses that to drive the compressor, the blower and the flaps.
When the control unit fails, the symptoms can vary: the air-con switches itself on and off, the temperature varies uncontrollably, the display does not work, or the buttons do not respond.
A new control unit costs 150 to 500 euros, used 40 to 150 euros. On some vehicles, the swap calls for coding via a diagnostic tool.
Electric heaters (PTC elements)
Many modern cars, especially diesels, have an electric PTC (Positive Temperature Coefficient) heater that helps warm the cabin until the engine warms up enough. Diesel engines are thermally more efficient than petrols, which is great for fuel use but poor for heating because they produce less waste heat.
The PTC heater sits in the heater/evaporator housing and can produce 1 to 3 kW of heat. When it fails, the cabin warms up slowly in winter, especially in city driving with short trips.
A new PTC heater costs 100 to 350 euros, used 30 to 100 euros. The swap is usually complicated because it calls for removing part of the dashboard.
Air-con pressure sensor
The air-con pressure switch/sensor tracks the refrigerant pressure in the system. If the pressure is too low (a leak) or too high (a blockage), the sensor sends a signal to the ECU which switches off the compressor to protect it.
When the sensor fails, the air-con can behave unpredictably: it works then stops, or it does not turn on at all even though the system is full. The diagnostic fault code usually shows the sensor problem clearly.
A new sensor costs 20 to 80 euros, used 8 to 25 euros. The swap is simple, but it calls for emptying and refilling the air-con system, which means a workshop visit.
Tips for buying used air-con parts
Here are practical tips specific to air-con and HVAC parts:
The compressor must be sealed - when the compressor is removed from the car, the system openings must be closed with plugs or tape so that moisture and dirt do not get inside. If the openings are open, the internal parts may have corroded and the compressor will not last long.
Ask about the reason for removal - if the air-con system on the donor vehicle had leak problems, contaminated refrigerant oil may have damaged the compressor too. If the compressor was taken from a car that was scrapped for other reasons, the odds are much better.
Check the refrigerant type - older cars use R134a, newer ones (from 2017) use R1234yf. The compressor must match your vehicle's refrigerant type.
Oil in the compressor - different compressors use different oils (PAG 46, PAG 100, PAG 150, POE). Check which type your system uses and make sure the compressor is filled with the correct oil.
How much you can save
Let us run the numbers for a typical air-con repair:
Scenario: replacing the compressor and the blower resistor
- New compressor: 450 euros, used: 150 euros
- New resistor: 35 euros, used: 10 euros
- Refrigerant and oil: 80 euros (same in both scenarios)
- Fitting: 200 euros (same in both scenarios)
Total with new parts: 765 euros
Total with used parts: 440 euros
Saving: 325 euros
That is a saving of more than 40 percent. And if we add the swap of a flap servo motor (a common related fault), the saving grows to more than 400 euros.
Where to find used air-con and HVAC parts
On the PoDi platform you can find every part of the air-con system and the heating. Simply describe what you need, give the vehicle details, and suppliers will send you offers.
We especially suggest asking for a kit if you need several parts. Suppliers who have a complete vehicle on hand can offer you packages at better prices than individual parts.
Air-con and heating are not a luxury, they are systems that affect driving comfort and safety (a foggy windscreen in winter is a safety risk!). With used parts, you can keep these systems working without big financial sacrifices. Check the parts, buy from reliable suppliers, and drive in comfort all year round.