Evacuation Of The Refrigerant Cycle; Achieved Final Vacuum; Evacuation Process - Valeo REVO Mode D'emploi

Evacuation of the refrigerant cycle

3 Evacuation of the refrigerant cycle
3.1.

Achieved final vacuum

In the entire refrigerant cycle a final vacuum of <10 mbar must be achie-
ved. It is also important that the required pressure of <10mbar must be
measurable at every point of the refrigerant cycle and not only at the
vacuum pump. The components of the refrigerant cycle, a spring-loaded
liquid hammer valve in the hot gas pipe, flow hampering service valves,
long hose pipes up to the vacuum pump etc. are unavoidably major re-
sistance against the flow during evacuation. Therefore, the vacuum
should be measured directly in the equipment (service connection in the
liquid line).
3.2.

Evacuation process

The vacuum pump and measuring devices to be used must be in a fault-
less condition. With reference to the documentation of the equipment
make sure that the oil in the vacuum pump is replaced at regular inter-
vals. The vacuum measuring devices must be suitable for the measuring
range up to 0.01 mbar. Normally, the equipment is evacuated after ser-
vice and/or repair work together with concluding Nitrogen pressure
check. The sequence of the listed points must be followed:
– Before connecting to the vacuum pump the circulation must be
"pressure-less".
– Open the magnetic valves in the refrigerant-liquid line (rooftop equip-
ment and front-end cabinet). This can be done through electrical
controls with the service program or permanent magnets which are
fixed to the valves instead of the magnetic coil.
– All blokking valves in the refrigerant cycle (compressor and service
valves) must be opened.
– A vacuum pump is connected by means of a large diameter (5/8")
hose to the service valves at the vehicle's bottom side.
– Using a second vacuum pump or another hose pipe the area bet-
ween the liquid hammer valve in the hot gas pipe and the liquefier
12
REVO Evacuation and Charging Instructions
must be additionally evacuated. For this purpose, the hose pipe
leading to the vacuum pump is connected to the service valve at the
collection exit point. In vehicles with 2 rooftop units (articulated bus)
the vacuum pump is connected to both service valves in the units.
Due to the significant pressure drop in the Schrader valves it is not
permissible to joint several service hose pipes with each other.
– The achieved vacuum can only be checked by two methods. In the
first method, a vacuum meter is connected while evacuating at the
farthest point of the refrigerant cycle. The second and considerably
safer method is to block the vacuum pump, wait until there is a pres-
sure balance in the refrigerant cycle and then to measure the achie-
ved vacuum in the system.
– After balancing the pressure the vacuum in the refrigerant cycle must
be still <10 mbar.
Causes for not achieving vacuum
The following causes may be present if the required vacuum is not
achieved:
– If moisture is present within the circulation a vapor pressure of
approx. 23 mbar sets in at 20 °C ambient temperature.
– If the oil temperature is > 60 °C vapor pressure in the refrigerant cy-
cle settles above 1 mbar.
– There may be leakages between vacuum pump and the service con-
nections.
– The refrigerant cycle was evacuated with opened gas ballast of the
vacuum pump.
– Vacuum pump and/or meter is defective.
– Vacuum pump has leakage.