Service Hints

Service
Hints:
In general, the R-134a air conditioning system performs and functions the same as a typical R-12 system. The following information is provided to assist the technician in diagnosing and repairing R-134a systems. This Service Information only provides R-134a specific hints and guidelines, and is not a substitute for proper BMW air conditioning Service Training.

When discharging the system (refrigerant recovery), it will be necessary to pull the system down to at least 10 inches of vacuum. At this point, the recycling station should be set to the HOLD mode by pressing the HOLD/ CONT key. The recycling station should be left in this mode for at least five minutes. This will allow frozen refrigerant to boil, vaporize, and gradually build up pressure. This discharge technique is mandatory on an R-134a system, or the recycling station will not have the opportunity to extract all of the refrigerant. After the five minute hold, resume the recycling by pressing the HOLD/CONT key again. This will restart the recycling station and remove the remaining refrigerant. The final total weight of the recovered refrigerant will be displayed on the recycling machine.

The recovery procedure should be followed by a complete evacuation "vacuuming" cycle at close to 30 inches of vacuum. This should be held for a minimum 30 minutes. The BMW R-134a system requires a higher level of cleanliness than R-12 systems. In the case of suspected moisture contamination, or a leak resulting in major loss of refrigerant, the recycling station may be adjusted to hold the evacuation cycle for additional time.

Any repair on the system which entalls opening the system mandates the replacement of the receiver-dryer. The R-134a system must remain completely dry. Using the old receiver-dryer (and associated desiccant) will only result in additional system failures in the future.

Any open pipes or air-conditioning components are to be sealed with plugs or caps immediately. The plugs/caps on replacements parts are only to be removed just before the component is installed. When servicing or replacing a compressor, condenser, or evaporator, always cap off all open fittings when not in use. Do not allow even a "failed" unit to sit open to the atmosphere. The lubricant and refrigerant will absorb moisture, and form an acid that damages new components and prevents analysis of "failed" units. After performing any work using the service fittings on the vehicle, the sealing caps should be replaced on the fittings and checked for a tight fit. These caps form part of the seal.

When adding PAG oil to the system, always pour an extra half-ounce into the injection bottle. Proceed with adding the PAG oil, but be careful not to actually inject the last half-ounce into the system. This technique keeps the oil level above the siphon tube at all times, and prevents air from being pulled into the evacuated system along with the PAG oil.