By Symptoms - Bosch ACS 751 Repair Instructions

4.2

By symptoms

Symptom
The gauge pressure
rises after the recov-
ery and recycling phase
The vacuum
phase does not start.
The leakage test at the end
of the vacuum phase failed.
Recharge is very slow or is
interrupted before the re-
quired quantity has been
filled to the vehicle.
The quantity of refrig-
erant filled does not
match the set amount
Compressor does not start
White smoke emanates
from the vacuum pump.
Robert Bosch GmbH
Description
Previous recovery was incomplete
/leak across the valves
The vacuum pump does not start.
Duration of the vacuum phase is too short.
Leakage in vehicle A/C system.
Leakage in the ACS 751/651.
Insufficient refrigerant in the
internal refrigerant container.
Pressure in the R134a cylinder is too low.
Scale for the refrigerant cylin-
der is not calibrated.
Mechanical obstruction for the scale
of the refrigerant cylinder.
R Power supply interrupted
R Check pressure switch
Aspirated ambient air
Troubleshooting | ACS 751/651 | 15 ACS 751/651 | 15
Troubleshooting
R Repeat recovery and check the gauge pres-
sure again at the end of recovery.
R Check if the plunger has worn out or if
there is contamination in the valve block.
Caution: Close the red and blue
valves on the internal refrigerant
cylinder before opening the solenoid.
R If the gauge pressure is high, per-
form recovery before vacuuming.
R Check the electrical and pipe connection to
the vacuum pump and associated solenoid.
R If the vacuum pump is on and yet, the
pressure does not decrease, check for
the pipe connection/blockage.
Vacuum phase duration is approximately 30 minutes
for vehicles with larger A/C systems (for example,
trucks require longer vacuum time).
Repair the vehicle A/C system.
Check HP, LP hoses and their connections.
Check if the plunger has worn out or if
there is contamination in the valve block.
Fill internal refrigerant cylinder with fresh re-
frigerant. The optimum quantity is 8 kg - 9 kg.
Fill internal refrigerant cylinder
with fresh refrigerant. The optimum pres-
sure is approximately 6-7 bar
Check the scale for the refrigerant cylinder with
a known weight. If the value does not match, cali-
brate the scale. See chapter 5 for more information.
R Check if the movement of the scale and the re-
frigerant cylinder is blocked mechanically by oth-
er components.
R Remove any obstructions for the scale.
Check the electrical connection of the power switch,
pressure switch, compressor and capacitor of the
compressor.
Inspect the vehicle A/C system and also the
ACS 751/651 for leaks and repair. Small quan-
tities of smoke in the first few minutes of op-
eration of the vacuum phase are permitted.
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2013-10-21