Husqvarna EZ4624 Operator's Manual page 60

Purging Procedures
Due to the effects air has on efficiency in hydrostatic
drive applications, it is critical that it is purged from the
system.
These purge procedures should be implemented any
time a hydrostatic system has been opened to facilitate
maintenance or any additional oil has been added to
the system.
The resulting symptoms in hydrostatic systems may
be:
1. Noisy operation.
2. Lack of power or drive after short term operation.
3. High operation temperature and excessive
expansion of oil.
Before starting, make sure the transaxle is at the
proper oil level. If it is not, fill to the specifications
outlined earlier.
The following procedures are best performed with the
vehicle drive wheels off the ground. Then repeated
under normal operating conditions.
1. Disengage the brake if activated.
2. With the bypass valve open and the engine running
at fast idle, slowly move the directional control in
both forward and reverse directions (5 or 6 times).
As air is purged from the unit, the oil level will drop.
3. With the bypass valve closed and the engine
running, slowly move the directional control in both
forward and reverse directions (5 to 6 times).
Check the oil level, and add oil as required after
stopping the engine.
4. It may be necessary to repeat Steps 2 and 3 until
all the air is completely purged from the system.
When the transaxle operates at normal noise levels
and moves smoothly forward and reverse at normal
speeds, then the transaxle is considered purged.
5. After the vehicle has been used two times, the oil
level should be checked while the oil is cold and
adjusted accordingly.
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