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APU pressure is low

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APU GTCP85-180L run normally.

Bleed air check > 35 psig

For starting engine, pressure at pressure gage is superior to 30 psig.

But with air conditionning cargo ans flight station comp on norm position, the pressure is under 22 psig.

The EGT is adjust to 620°c

RPM to 100%.

Bleed air valve APU is checked.

After that, the pressure is always under 22 psig.

With only one air conditionning comp, how much is the pressure drop ?


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With cc pack on bleed air pressure should be around 35ps (32psi minimum), both packs should max out egt and pressure as low as 10psi, and unloaded should be above 38psi. Check air pressure regulator for 18.5 to 19.5psi


Assuming load control valve and thermostat have been replaced, you are probably looking at erroded compressor, and therefore apu change

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After adjustment of pneumatic thermostat at 620°C and RPM at 100%, we have a pressure at 21 psig max. (With 2 cc pack).

The adjustment of air pressure regulator may be doing only with analyzer APU ?

If the compressor was eroded, the pressure was under 22 psig for start engine like with 2 cc pack ?

Do know if exist documentation on APU compressor liquid wash like engine (SP240) ?


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