When the outside air con tains smoke, odors, high
humidity, or if r apid coolin g is desired, interior air
can by recir cula ted by selecting the Recirculation
Mode with the mode cont rol kn ob. The mode contr ol
knob opera tes th e recirculation door thr ough use of a
vacu um actu ator. When t he Recirculation Mode is
selected, th e recirculation door is closed to pr even t
outside air fr om en tering the passenger compar t-
ment.
To maintain minimum eva por ator temper ature an d
pr event eva por ator freezing, an evaporator t empera -
ture sensor is used.
The A/C system is designed for the use of non-CFC,
R-134a refrigerant only a nd u ses an expa nsion valve
to meter refrigera nt flow t o the evapora tor.
DI AGN OSI S AN D T EST I N G
A/ CPERFORMANCE
The A/C system is designed t o provide th e passen-
ger compartment wit h low tempera ture and low
humidity air. The A/C evapor ator, loca ted in the
HVAC housing is cooled t o t empera tures near the
freezing point. As warm da mp air pa sses over th e
fins of t he A/C evapora tor, the air transfer s its hea t
to t he refrigera nt in the evapora tor coils a nd the
moistu re in t he air condenses on the evaporator fins.
During periods of high hea t and hu midit y, a n A/C
system will be more effective in the Recircu lat ion
mode (m ax-A/C). Wit h the syst em in t he Recircu la-
tion mode, only air from the passenger compartment
pa sses th rough th e A/C evaporator. As t he passenger
compart ment air dehumidifies, the A/C system per-
formance levels r ise.
Humidity has a n important bear ing on th e tem per-
ature of the air delivered to the in terior of the veh i-
cle. It is import ant to under st and the effect t hat
humidity has on t he performance of the A/C system.
When humidit y is h igh , the A/C evaporator h as t o
perform a double duty. It mu st lower th e air temper-
ature, and it must lower the temperatur e of the
moistu re in th e air th at conden ses on the evaporator
fins. Conden sing the moistur e in the air tr ansfer s
heat energy into th e eva por ator fins an d coils. This
reduces the amou nt of h eat the A/C evaporator can
absorb from th e air. High humidity gr eatly reduces
the ability of t he A/C evaporator to lower the tem per-
ature of the air.
However, eva por ator capacit y used to reduce th e
amount of moistu re in the air is not wasted. Wrin g-
ing some of th e moisture out of th e air ent ering the
vehicle a dds to the com fort of the passengers.
Although, an owner m ay expect too much from t heir
A/C system on humid days. A performance test is the
best wa y t o det er m in e wh et h er t h e s yst em is p er-
forming up to design sta ndards. This t est also pro-
vides valu able clues as to th e possible cause of
trouble with the A/C syst em. The a mbien t air tem-
perat ure in t he location where th e vehicle will be
tested must be a minim um of 21° C (70° F) for this
test.
A/ CPERFORMANCETEST
WARNING: Refer to the applicable warnings and
cautions for this system before performing the fol-
lowing operation (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - WARNINGS) and (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
CAUTIONS). Failure to follow the warnings and cau-
tions could result in possible personal injury or
death.
NOTE: Very specific instructions and conditions
pertain to this procedure which are significantly dif-
ferent than procedures used in other vehicle appli-
cations. Follow each step in the order they are
presented. Do not skip steps or change conditions
from those stated or results will be adversely
affected and invalid.
NOTE: When connecting the service equipment
coupling to the line fitting, verify that the valve of
the coupling is fully closed. This will reduce the
amount of effort required to make the connection.
(1) Check for dia gnostic trouble codes using a
DRBII I! scan tool. If no DTCs are foun d in the
engine control module (ECM), go to Step 2. If any
DTCs are found, repa ir as requir ed, then proceed to
Step 2.
(2) Pla ce th e vehicle in th e shade and oper ate the
heat ing-A/C system under the following conditions.
• Engine a t idle a t operat ing temper atur e
• All doors or windows open
• Transaxle in Neu tr al
• All A/C du ct louvers open
• A/C-h eater con trols set to fresh air (NOT Recir-
cula te), full cool, pa nel mode, high blower and with
A/C compressor en gaged.
NOTE: The A/C compressor clutch is de-energized
under any of the following conditions:
• Restricted compressor (thermal fuse in the pul-
ley)
• Low pressure in the system
• Low evaporator temperature
• Hard acceleration (WOT)
• High coolant temperatures
(3) In sert a thermom eter in t he driver side center
pa nel air outlet and operat e the A/C system unt il the
ther momet er temper ature stabilizes.
VA HEATING & AIR CONDITIONING 24 - 3
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