A/C Not Cooling — Causes and When a Recharge Is Enough

A car’s air conditioning is a closed system: the compressor pressurises the refrigerant, the condenser releases the heat outside, and the evaporator behind the dashboard cools the air going into the cabin. When the vents start blowing cool instead of cold air — or warm air — the cause is almost always one of these parts or the amount of refrigerant.

The most common causes

• Low refrigerant. Every system loses a little refrigerant through its seals over the years. A larger loss, though, means a leak — most often at the condenser (it sits at the front and takes stones and moisture), at the hoses and joints, or at the compressor seal.
• The compressor does not engage. The cause can be the clutch, a fuse, a relay or a pressure sensor. On many modern cars the compressor is controlled electronically and will not switch on at all if the system pressure is too low.
• A blocked or dirty condenser. If the condenser is covered in dust, leaves and insects, or the fan in front of it does not work, the system cannot get rid of the heat and cools poorly, especially in traffic.
• An expansion valve or evaporator problem. A blocked valve or a leaking evaporator gives weak cooling and sometimes frosted pipes.
• A clogged cabin filter. The system may cool normally, but little air gets through the clogged filter and the cabin cools slowly.

Why a recharge without a check is often wasted money

If the system has lost much of its refrigerant, there is a leak. A recharge will bring the cold air back — but only until the refrigerant leaks out again, sometimes within weeks. That is why we check the pressure and the tightness of the system before recharging: the system is put under vacuum and we watch whether the vacuum holds. If it does not, the leak is found and fixed first.

A recharge alone is enough when the system is tight and the refrigerant has dropped gradually over the years — usually on a car whose A/C has not been serviced for a long time.

R134a or R1234yf

Older cars use R134a refrigerant; most new cars in the EU since 2017 use R1234yf. The two are not interchangeable and need different equipment. The type is shown on a label under the bonnet. DIY recharge cans are not recommended: without the exact amount and without checking for moisture and leaks, the system may cool worse and the compressor can be damaged.

Signs you should not ignore

• Noise or rattling when the A/C is switched on — the compressor or its clutch may be worn.
• A bad smell from the vents — bacteria and mould grow on the evaporator; cleaning the evaporator and replacing the cabin filter helps.
• Misted windows that do not clear with the A/C on.
• Water in the cabin, usually in the passenger footwell — a blocked evaporator drain.

How to make the system last longer

• Run the A/C for a few minutes at least once a week, in winter too. Oil circulates with the refrigerant, lubricating the compressor and keeping the seals from drying out.
• Replace the cabin filter on the manufacturer’s schedule — more often if you drive in dusty conditions.
• Check how well the A/C works before summer, not in the first hot week.

If the A/C cools poorly or not at all, book an appointment — we will check the system’s pressure and tightness and tell you whether a recharge is enough or a repair is needed.