SPRING-RETURN 2600034 - Caterpillar

Machines Equipped With Air ConditioningIt has been reported that some dealer servicemen are using an incorrect vacuum source when servicing air conditioning systems. Such incorrect equipment includes service truck inlet manifold vacuum, or a belt-driven brake vacuum boost pump. Using such incorrect equipment will not evacuate all the air or water in the system. The left-over air and water will result in poor air conditioner performance, and short component life.
Even a small amount of air remaining in an air conditioner will cause: ... Poor cooling because the air does not change phase (go from liquid to vapor and back to liquid) as the Freon does.... Sludging due to oxidation of the oil in the system.
The purpose of evacuating an air conditioning system is to remove air and water from the inside of the system. Water can be in the system in three forms: water vapor, liquid, and/or dissolved in the refrigerant oil.
A trace of water in the system will cause: ... Blockage of the orifice in the expansion valve (in freezing conditions producing ice in the lines).... Sludging due to reaction between the water and the oil.... Corrosion of metal parts in the system due to rusting of steel parts. Corrosion is also caused by hydrofluoric acid produced by a reaction between Freon and water.
A high vacuum will remove most of the air and water vapor. The drops of water will be removed instantly because the water boils rapidly in the high vacuum. Water dissolved in oil, however, will take much longer to become a vapor and then be suctioned out of the system. For this reason, a vacuum of 27 in Hg minimum must be applied for at least 30 minutes.
The service truck inlet manifold or brake boost pump may only achieve 20 to 21 in Hg, and are inadequate for air conditioner servicing.
Refer to the new Air Conditioning and Heating Service Manual, Form SENR3334 for the complete evacuation and charging procedure.