B737-200 hyd. snag

[chilkoot]

Here's a good snag for you 737 classics entousiasts!

I've got an intermittent snag on one of my B737-200, and it's a real head scratcher. Here it is:
Sometimes on approach, when crew selects flaps one, "A" sys. hyd. pressure drops for a second to 500psi and below. Both "A" sys. low pressure lights come on and of course the hyd. annonciator. It seems to be happening only when the hydraulic quantity sometimes goes up a gallon too high on the indicator and then comes back down. All that happening in flight. It never happens on climb when gears are selected up and engines are at higher power settings.
Now, here's what I tried.
All hyd. filters have been replaced, including the hyd. res. air system.
Hyd. press. module relief valve (thinking it was dumping pressure)
Hyd. res. air pressure regulator (twice)

I know somebody's probably seen this problem before but it's a first for me. I would appreciate some input.

Puzzled

[Mr @ Spotty M]

Have a look to see if you have any Hyd fuses in the system, it's only a thought.

[excon]

mate, its sounds like an unusual one to me, I havent heard of that defect b4, but the first component i personally would change would be the complete sys a hydraulic pressure module as you appear to be getting a genuine, albeit brief and intermittant low pressure situation.
let us know when u fix it, and good luck
rgds
excon

[chilkoot]

Thanks for the feedback y'all!
I'll let you guys know what I find:ok:

[TURIN]

Used to get this one a lot on the old -200 series. Almost always the reservoir pressurisation module freezing.

It was supposed to be drained every night but ho-hum you had to get a set of steps and if you were in the boonies with no transport, and your next jet was on finals.........

Also try cleaning the filter in the pressurisation module.:ok: