Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Possible Refrigerant Circuit Concerns
Test requirements
- Electrical system, vacuum system and air duct fault-finding has not revealed any faults , air conditioner Guided Fault Finding function → Electrical Wiring Diagrams, Troubleshooting and Component Locations and → 87 - Air conditioning
- No fault revealed by air conditioner On Board Diagnostic (OBD) (e.g. using fault read out device V.A.G 1551 → 87 - Air conditioning or , air conditioner Guided Fault Finding function ); no compressor shutoff criterion displayed in measured value block (vehicles with "air conditioner" On Board Diagnostic (OBD) only)
Possible Concerns
- For all complaints marked *, refer to → Refrigerant Circuit, Checking Pressures with A/C Service Station "Checking pressures".
- If a malfunction occurs at only one evaporator in vehicles with two evaporators, also check pressures in the refrigerant circuit.
- Total cooling system failure *
- Insufficient cooling output at all vehicle or engine speeds *
- No or insufficient cooling after driving a few miles *
- No cooling or insufficient cooling at one or both evaporator(s) (on vehicles with two evaporators).*
- Compressor, A/C Clutch N25 or A/C Compressor Regulator Valve N280 shut off by pressure switch (e.g. A/C Refrigerant Low Pressure Switch F73 , A/C Refrigerant High Pressure Switch F118 , A/C Pressure Switch F129 or A/C Control Head E87 or Climatronic Control Module J255 ) on account of excessive or inadequate pressure *
- No or sharp decrease in fresh-air supply after driving several miles (evaporator iced up) *
Other possible problems:
Compressor noise
- Re-tighten securing bolts for compressor and compressor bracket using a torque wrench.
- Check routing of refrigerant pipes; they must not touch other components and must not be subject to strain (align if necessary).
Noise (refrigerant hammer) occurring immediately after switching on air conditioner and/or when cornering or braking:
- Discharge, evacuate and recharge refrigerant circuit (too much refrigerant in circuit).
- Too much refrigerant oil in the circuit may also result in this problem (no adjustment of refrigerant oil quantity, for example, on replacing compressor).
Water sprays out of vents (in instrument panel or footwell) although air conditioning system is otherwise functioning properly:
- Check proper routing of condensate drain; it must not be crushed or kinked.
- Check condensate drain valve; it must not be gummed up with wax or underseal and must close properly.
- Check plenum chamber cover; it must not be damaged and must be properly installed (to stop water running into evaporator).
- Check water drains in plenum chamber; they must not be blocked (e.g. by leaves).
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.