MTC Air Conditioner - Trouble Diagnoses for Unusual Pressure

TROUBLE DIAGNOSIS
MTC-105
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MTC
Revision: January 2005 2004 Quest
TROUBLE DIAGNOSES FOR UNUSUAL PRESSURE
Whenever system′s high and/or low side pressure is unusual, diagnose using a manifold gauge. The marker
above the gauge scale in the following tables indicates the standard (usual) pressure range. Since the stan-
dard (usual) pressure, however, differs from vehicle to vehicle, refer to above table (Ambient air temperature-
to-operating pressure table).
Both High- and Low-pressure Sides are Too High
High-pressure Side is Too High and Low-pressure Side is Too Low
Gauge indication Refrigerant cycle Probable cause Corrective action
Both high- and low-pressure sides
are too high.
Pressure is reduced soon
after water is splashed on
condenser.
Excessive refrigerant charge
in refrigeration cycle.
Reduce refrigerant until speci-
fied pressure is obtained.
Air suction by cooling fan is
insufficient.
Insufficient condenser cooling
performance.
↓
1. Condenser fins are clogged.
2. Improper fan rotation of
cooling fan.
● Clean condenser.
● Check and repair cooling fan
as necessary.
● Low-pressure pipe is not
cold.
● When compressor is
stopped high-pressure
value quickly drops by
approximately 196 kPa (2
kg/cm
2
, 28 psi). It then
decreases gradually there-
after.
Poor heat exchange in con-
denser.
(After compressor operation
stops, high-pressure
decreases too slowly.)
↓
Air in refrigeration cycle.
Evacuate repeatedly and
recharge system.
Engine tends to overheat.
Engine cooling systems mal-
function.
Check and repair engine cool-
ing system.
● An area of the low-pres-
sure pipe is colder than
areas near the evaporator
outlet.
● Plates are sometimes cov-
ered with frost.
● Excessive liquid refrigerant
on low-pressure side.
● Excessive refrigerant dis-
charge flow.
● Expansion valve is open a
little compared with the
specification.
↓
Improper expansion valve
adjustment.
Replace expansion valve.
AC359A
Gauge indication Refrigerant cycle Probable cause Corrective action
High-pressure side is too high and
low-pressure side is too low.
Upper side of condenser and
high-pressure side are hot,
however, liquid tank is not so
hot.
High-pressure tube or parts
located between compressor
and condenser are clogged or
crushed.
● Check and repair or replace
malfunctioning parts.
● Check lubricant for contami-
nation.
AC360A