Interpreting Abnormal System Pressures; Thermostatic Or Icing Switch Test; Receiver Dryer Test .1; Common Adjustments And Repairs - Ford COUGAR 1968 Shop Manual

16-28
GROUP 16
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Ventilating, Heating, And Accessories
higher system pressures. The lowest
figures given are for an ambient (sur-
rounding air) temperature of 75 de-
grees F., 50% relative humidity.
The low pressure gauge should in-
dicate a pressure of from 12-50 p.s.i.
The high pressure gauge should indi-
cate a pressure of 120-300 p.s.i.
A t idle speed and a surrounding
air temperature of 100 degrees
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110
degrees
F.,
the high pressure may go
as high as 300 pounds or more.
If it
becomes necessary to operate the air
conditioner under these conditions,
keep the high pressure down with a
fan directed at the condenser and
radiator.
I N T E R P R E T I N G A B N O R M A L
S Y S T E M P R E S S U R E S
Low Pressure Below Normal,
H i g h Pressure Normal
These pressures indicate a low charge
or a restriction between the receiver
and the expansion valve or between
the expansion valve and the low pres-
sure service valve. If the low pressure
is actually a vacuum, the ex.pansion
valve is probably closed tightly. Check
the expansion valve and replace it i f
required.
Check the system between the re-
ceiver outlet and the expansion valve
for restrictions, by feeling all of the
connections and components. Any
portion that is cold to the touch or
that frosts up, with the pressures as
indicated here, is restricting the re-
frigerant flow.
Low Pressure Above Normal,
High
Pressure Normal
Check the heater water valve to be
sure that it is closed. Operate the
system on MAX A/C and be sure
that the outside air door is closed.
H i g h Pressure Below Normal
or Low Pressure Above Normal
Check the compressor.
With the system operating, close the
suction service valve. The suction
pressure gauge should read at least
20 inches of vacuum within 30
seconds.
Disengage the clutch. The suction
gauge should read below zero psi
for at least one minute.
I f the compressor does not satisfy
these two conditions after at least
3 cycles of the clutch, the compres-
sor has either a blown head gasket
or faulty valves. Remove the head
and inspect for damage. Repair as
required. Refer to Section 3.
A compressor with scored cylinder
walls or pieces of metal imbedded
in the pistons should be replaced.
Check the expansion valve.
Mustang and Cougar:
Check the expansion valve bulb
clamp to assure good contact. The
bulb and clamp must be clean and
tight and properly wrapped with
insulation.
If the bulb is clamped and insulated
properly and the suction pressure is
still too high, replace the expansion
valve.
Falcon, Fairlane, and Montego:
I f the compressor is OK and the
suction pressure is too high, replace
the expansion valve.
H i g h Pressure Above Normal
High compressor head pressures are
caused by an overcharge of refrigerant,
condenser air passages clogged, a
restriction between the condenser inlet
and the receiver, or high surrounding
air temperatures. Check the condenser
fins for dirt or insects and clean as
required. If the high pressure is still
excessive, discharge the system
through the discharge service valve.
Check for a restricted condenser or
a restriction between the condenser
and the receiver. Evacuate the system
and charge with the specified amount
of Refrigerant 12.
T H E R M O S T A T I C O R
I C I N G S W I T C H T E S T
Fill a container with crushed ice,
salt and water. Put enough salt in the
water so that the temperature of the
solution is 25 degrees F. or lower.
Set the thermostatic control switch
(Mustang and Cougar only) for the
maximum cooling position. This is
the maximum clockwise or counter-
clockwise position at which the switch
contacts are closed at room tem-
perature. Use a self-powered test
light or ohmmeter connected to the
switch terminals to check whether
or not the switch is closed.
Place the sensing tube in the ice,
salt and water solution. The ther-
mostatic or icing switch contact
points.should open and remain open
while the tube is in the solution.
Remove the sensing tube from the
solution. As the tube warms up, the
switch contacts should close. An ohm-
meter check of the contacts should
show a resistance of less than an ohm.
I f a resistance of an ohm or more
occurs, replace the switch.
M a k e cer-
tain that no salt water gets into the
control.
If the control fails to function
as outlined, it must be replaced.
R E C E I V E R - D R Y E R T E S T
Operate the air conditioner for
about five minutes; .then, feel the
receiver-dryer outlet. If the outlet
is cold, it indicates that the unit is
restricting the refrigerant flow, and
the receiver-dryer must be replaced.
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"COMMON .ADJUSTMENTS .AND' REPAIRS
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D I S C H A R G I N G THE SYSTEM exhaust outlet. Set both manifold
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gauge valve at the'maximum counter-
Discharge the refrigerant from the clockwise or open position. Open
system .bifore replacing any part of
both service valves a slight amount
the system, except the compressor. (Figs. 9 and 10) and allow the re-
To discharge the system, connect
frigerant to discharge slowly from the
the manifold gauge set.to the system. system.
Do not connect the manifold center
connection hoses to the Refrigerant-
D o not allow
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the refrigerant to
12 tank, or vacuum pump. Place the
rush out, as the oil in the compres-
open end of these hoses in a garage
sor will be forced out along with it.
E V A C U A T I N G THE SYSTEM
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..Attach the manifold gauge set,
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tank of Refrigerant-12 and a vac-
uum pump to the system. Make cer-
tain that the Refrigerant-I2 tank
valve is tightly closed. Set both serv-
ice valves to the mid-position. Open
both manifold valves. .Release any
pressure in the system. Open the
vacuum pump valve and run the