Porsche P-80 2005, Руководство пользователя

Страница: 17 / 108

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair
Page 1.11
Condenser
The condenser is a heat exchanger located in the front of
the vehicle. It is similar to the engine radiator and has a
large surface area for efficient heat transfer. Some
Porsche models use two condensers. The condenser is on
the A/C system high side and contains high pressure
refrigerant.
The condenser allows high pressure, hot refrigerant gas to
give off heat energy to cooler air passing through the
condenser fins. Forward motion of the vehicle and electric
fans both promote this air flow.
The refrigerant changes state in the condenser in this
sequence:
• High pressure refrigerant enters the condenser as a hot
gas: 60-100° C (140-212° F).
• The heat energy that was absorbed by the refrigerant in
the evaporator is transferred to the cooler ambient air
passing over the condenser's tubes and fins.
• The refrigerant gas gives up both sensible heat and
large amounts of latent heat energy to the cooler
ambient air.
• The gas cools, changes state and condenses to a
liquid.
• The refrigerant leaves the condenser as a very warm
high pressure liquid.
The DME controls system cooling fans based on engine
load. When the A/C is ON, the electric cooling fan comes
ON to improve airflow and heat transfer.
Receiver/Dryer
911 Carrera (996) Receiver/Dryer
The receiver/dryer is a reservoir for refrigerant on the
system high pressure side. It is located between the
condenser outlet and evaporator inlet. Condensed liquid
refrigerant flows into the receiver dryer from the
condenser.
As heat load on the A/C system changes, more or less
refrigerant will be in the liquid state. Also, over time, some
refrigerant will escape past seals. The receiver/dryer acts
as a reservoir for refrigerant to compensate for these
conditions. The pickup tube in the receiver/dryer ensures
that only liquid refrigerant is sent to the expansion valve.
The receiver/dryer contains a desiccant to remove
moisture from the system. The desiccant can absorb 6-12
g of water. This is not much, and moisture must be kept
out of the system during repairs.
R-12 systems included a sight glass on top of the
receiver/dryer The flow of liquid refrigerant could be seen
through the glass and a stream of bubbles indicated low
refrigerant level. A sight glass was used on some R-134a
systems in the early 1990’s. A/C service equipment accu-
rately measures the refrigerant charge by weight, making
the sight glass unnecessary.
When retrofitting an R-12 system with R-134a, always
replace the receiver/dryer as R-12 desiccants are not
compatible with R-134a, and the desiccant will be perma-
nently saturated with mineral oil.