Beech 1900D Pressurization
Evening
Could any Engineers please lend some advice/experience with the following issue:
In the cruise at FL215 and 235 the pressurization rate fluctuates between 500 feet climbing and 1000 feet descending, this happens constantly every minute or so when the Enviro control is set on auto and temp at max cool. When the Enviro is set at manual cool it stabilisers.Maz diff is reached in both settings.
The following has been completed with no affect.
1. ACM and Heat Exchanger cleaned
2. Pressurization Controller changed
3. Outflow Valves changed
4. Pneumatic Relay changed
Any ideas would be great.thamks