Beech 1900D Pressurization

[PWC]

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

[bbrunton]

Did you have the pressurization controller set to 500 feet above your cruise altitude as is recommended?


You say the cabin was at max differential. At cruise, setting the controller to +500 feet means that the cabin will be a couple of tenths less than maximum. If the cabin is at maximum differential, and the outflow and safety vales are not set to the same maximum differential setting (highly unlikley) then they will be fighting each other for control of the maximum differential in the cabin.

Try setting the controller a little higher and getting a slightly lower differential.

If that does not fix it, look for a sticky valve or something blocking the airflow to them.


Bill

[MungoP]

The Beech recommendation is to set it at 1000ft above cruise alt...

[PWC]

Thanks Ben

Will take a look tomorrow.

Cheers

[Golden Rivit]

Thru and Bypass valves?

[RobRW]

Hey mate,

We had a similar problem on a 1900D.

Changed out ACM and it was sorted.

(noted you said you cleaned the ACM, might still be U/S due to not spinning up enough).

[PWC]

Hey RobRW

Thanks for the info,after further trouble shooting we found the RH Engine Pre-cooler to have a 3 inch crack which is leaking a serious amount of P3.
The snag has actually progressed a bit,the Cabin alt high annunciator comes on in the cruise with the rate still hunting between 500 foot climb and 1000 foot descending.Only once the Enviro is placed on MAN COOL and more heat is introducd into the cabin(bypassing the ACM) does the Max diff and cabin alt high sort its self out.The Pre-Cooler will be replaced within the next few days so will update the thread if the snag clears.

Cheers Gents,thanks again

[RobRW]

Any updates on the 1900? Had a pressurisation problem on one today and was thinking of your snag.

[stankou]

hi

Ask your pilot to turn full hot on temp during flight and let you know if press is stab.

No so easy to check on ground. If there is a difference between cold and hot, that means you have a bad ACM; maybe still running but not at constant speed, creating fluctuation on press system.

cheers.

[Corey Goss]

hi

Ask your pilot to turn full hot on temp during flight and let you know if press is stab.

No so easy to check on ground. If there is a difference between cold and hot, that means you have a bad ACM; maybe still running but not at constant speed, creating fluctuation on press system.

cheers.

We had this same issue, we changed the ACM. When I pulled out the ACM the turbine was seized up.... funny that this is not in the troubleshooting guide!

Funny thing is no one believed me when I said the acm was bad.... until I pulled it out and showed them the thing was seized up!

Also discovered that removing the plenum on the aft side allows enough access to see if the turbine is seized up via rotating the heat exchanger fan.