Ford 2003 Mustang Workshop Manual page 3040

Refrigerant R-134a must not be mixed with air for leak testing or used with air for any
other purpose above atmospheric pressure. R-134a is combustible when mixed with high
concentrations of air and higher pressures.
A number of manufacturers are producing alternative refrigerant products that are
designed to be used instead of R-134a refrigerant. The use of any unauthorized
substitute refrigerant can severely damage the A/C components. If repair is required, use
only new or recycled refrigerant R-134a.
CAUTION: To avoid contamination of the A/C system, always observe the following:
Keep service tools and the work area clean.
Never open or loosen a connection before discharging the system.
When loosening a connection, if any residual pressure is evident, allow it to leak out
before opening the fitting.
Evacuate a system that has been opened to install a new component or one that has
been discharged through leakage before charging.
Seal an open fitting with a cap or plug immediately after disconnecting a component
from the system.
Clean the outside of the fittings thoroughly before disconnecting a component from the
system.
Do not remove the sealing caps from a new component until ready to install.
Refrigerant oil will absorb moisture from the atmosphere if left uncapped. Do not open
an oil container until ready to use, and install the cap immediately after using. Store the
oil in a clean, moisture-free container.
Install a new O-ring seal before connecting an open fitting. Coat the fitting and the O-ring
seal with refrigerant oil before connecting.
When installing a refrigerant line, avoid sharp bends. Position the line away from the
exhaust or any sharp edges that can chafe the line.
Do not open a refrigerant system or uncap a new component unless it is as close as
possible to room temperature. This will prevent condensation from forming inside a
component that is cooler than the surrounding air.
The manual climate control system heats or cools the vehicle depending on the function selector
switch position and the temperature selected.
The function selector switch position determines heating or cooling and air distribution.
The temperature control setting determines the air temperature.
The heater blower motor switch (18578) varies the blower motor speed.
Principles of Operation
There are four main principles involved with the basic theory of operation:
heat transfer
latent heat of vaporization
relative humidity
effects of pressure
Heat Transfer