Why does the car air conditioning only cool when stepping on the accelerator?
3 Answers
The reasons why the car air conditioning only cools when stepping on the accelerator are: 1. Insufficient battery voltage; 2. Slipping of the air conditioning compressor belt; 3. Damage to the air conditioning compressor. The car air conditioning system consists of a compressor, electronic control clutch, condenser, evaporator, expansion valve, receiver-drier, pipelines, condenser fan, vacuum solenoid valve, idle speed controller, and control system, which are divided into high-pressure and low-pressure pipelines. The functions of car air conditioning are: 1. To adjust and control the temperature, humidity, air cleanliness, and air flow inside the car cabin to a better state, providing passengers with a comfortable environment and reducing travel fatigue; 2. To create good working conditions for the driver, serving as an important ventilation device for ensuring safe driving.
Once when I was driving an old Jetta, I encountered this same issue - the AC would weaken as soon as I let off the gas. After inspection, I found the compressor electromagnetic clutch wasn't engaging steadily - at idle speed the voltage wasn't sufficient to maintain proper engagement, only when revving the engine by pressing the accelerator would it have enough power. I also checked the alternator belt, which indeed showed signs of aging and slippage. If there are oil stains on the AC piping, it's most likely refrigerant leakage - when pressure is insufficient, the compressor requires higher RPM to function properly. By the way, if the condenser gets clogged with willow catkins like a carpet, poor heat dissipation will also reduce cooling efficiency. In such cases, simply rinsing the radiator fins with a water gun during car wash can provide relief.
My decade-old SUV has this exact issue - it blows hot air at red lights, making passengers on the front seat constantly wipe sweat. Later diagnosis showed insufficient refrigerant with low-side pressure barely maintaining 1.2bar (normal operation requires over 1.5bar), forcing the compressor to work at high RPM to build pressure. The mechanic said such slow leaks usually hide at condenser joints or compressor shaft seals, requiring UV dye detection. Also, if the expansion valve gets stuck slightly open, insufficient refrigerant flow can cause similar symptoms, though fixing this requires dashboard removal which is quite troublesome.
