Hello Dr. Elctron: If you can take out the covers and see it in operation you can get to realize if the filter or capillary is covered, it also verifies the consumption that also guides you in the possible cause of the problem. From the moment it starts you have that low pressure? I assume that the condenser has already been cleaned and the correct operation of the condenser forger and its capacitor has been verified. This is the option without spending anything on materials. The other is to add some refrigerant and see how it reacts, without adding and the pressure does not rise, well it can already be a partial obstruction of the filter or capillary. Luck, comment your results.