A/C - Reduced Performance When Idling
SECTION8
GROUP
87
NO.
953
DATE
Oct. 1995
RE:
Checking pressure switch operation
900 1993-
REFERENCE:
TP 8701201, SECTION 8 (87), CLIMATE UNITS; 700/900 1982-
SB 8-87-954; 7/95
Checking pressure switch operation
Reduced A/C performance when the engine is idling may be due to the low or high-speed A/C system pressure switches (Pressostat) starting the engine coolant fan (FC) at too high a pressure, and stopping it too early.
This Service Bulletin describes how to measure the pressure when the pressure switches (Pressostat) start the engine coolant fan (FC). The following method requires the correct volume of R134a in the A/C system. There should be no other faults causing reduced A/C performance.
Special Tools:
Plastic hose diameter 7 mm (9/32"), length = 1.5 metres (5 ft)
Cable, 1 sq.mm, length 2 + 2 metres (6.5 + 6.5 ft)
Cable, 1 sq.mm, length = 10 cm (4")
A/C nipple, P/N 9512667-8
Cable terminal, P/N 970789-4, 1
Cable terminal, P/N 969781-4, 1
Cable terminal, P/N 978258-2, 2
Moisture proof sleeve, P/N 3523813-8, 1
Butt connector, P/N 9130476-6
Insulation tape
Make up cable harnesses:
- One 10 cm (4") long cable with cable terminal, P/N 9697814 at both ends.
- One cable harness made of 2 x 2 meters long cables. Route cables through plastic hose.
Install cable terminal 970789-4 at one end of the cable harness and two cable terminals 978258-2 at the other end.
Tape the cable terminals with insulation tape to avoid contact between the cables.
The following method requires the correct volume of R134a in the A/C system. There should be no other faults causing reduced A/C performance.
Method, preparations
Remove grille.
For the 960, model year 1993-:
- Remove air guide.
- Undo the bumper and pull forward 10 cm (4").
All 900 series model year 1992-:
Remove high pressure shut-off pressure switch (Pressostat) (violet)
Install nipple, P/N 9512667-8 (see arrow on image above).
Connect R134a drainage/recycling unit to nipple.
Bridge the high pressure shut-off (violet) connector with the 10 cm (4") cable.
Remove the fan control (FC) relay in front of the battery shelf.
Remove the middle connector.
Connect one cable terminal of the 2 metres (6.5 ft) cable to position 1 on the FC relay (low-speed).
Position 2 on the FC relay should be left empty.
Connect the other cable terminal of the 2 metres (6.5 ft) cable to ground.
Check the low-speed pressure switch (Pressostat)
Disconnect the connector from the low-speed pressure switch (Pressostat) (grey contact).
Connect the free end of the 2 meters (6.5 ft) cable to the pressure switch (Pressostat).
Start engine.
Turn the A/C system to maximum cooling.
Check the pressure on the high pressure gauge on the drainage/recycling unit. The low-speed pressure switch (Pressostat) should start the engine coolant fan (FC) at 18 +/- 1 bar (260 +/- 15 psi).
Note:
Pressure must not exceed 28 bar (406 psi). If this occurs switch off the engine
Turn off engine.
If the low-speed pressure switch (Pressostat) P/N 6848632-5 starts the fan at a pressure higher than 19 bar, (275 psi) the switch should be replaced.
Move the 2-meter cable terminal from position 1 to position 2 on the FC relay.
Check the high-speed pressure switch (Pressostat)
Disconnect the connector (brown) from the high pressure switch (Pressostat).
Move the 2 meters (6.5 ft) cable from the low-speed pressure switch (Pressostat) to the high-speed pressure switch (Pressostat) (brown).
Connect the connector to the low-speed pressure switch (Pressostat) (grey connector).
Start engine.
Turn the A/C system to maximum cooling
Check the pressure on the high pressure gauge on the drainage/recycling unit. The high-speed pressure switch (Pressostat) should start the engine coolant fan (FC) at 23 +/- 1 bar (333 +/- 15 psi).
Warning:
Pressure must not exceed 28 bar (406 psi). If this occurs switch off the engine
Turn off engine.
If the high-speed pressure switch (Pressostat) P/N 6848533-3 starts the fan at a pressure higher than 24 bar (348 psi) the switch should be replaced.
Final operations
Close the connector valve to the drainage/recycling unit and disconnect its hose from the car.
Remove nipple 9512667-8.
Reinstall high pressure shut-off switch (Pressostat). Remove jumper cable and connect the violet connector.
Connect the brown connector to the high-speed pressure switch (Pressostat).
Reinstall relay in original location.
Connect the connector valve to the service valve on the dryer bottle and top-up with 100 g (3.53 oz) R134a to compensate for the refrigerant drained into the drainage/recycling unit hose.
NOTE:
This assumes that the car had the correct volume R134a prior to pressure testing.
Reinstall air guide and bumper where necessary.
WARRANTY STATEMENT: Claims may be submitted under the New Car Limited Warranty when there is a documented customer complaint using claim type: 01