A/C Help. Expansion Valve blocked? Drier Clogged?

[Syncade]

My air conditioning is confusing me. I have searched all morning for answers.

CAR: 1997 240sx SE. All OEM. 198,000 miles.


Basically I took my car to get a recharge this morning (AC only gets cold at highway speeds). The mechanic showed me:

LOW PRESSURE SIDE is way too high (70ish)

HIGH PRESSURE SIDE was basically normal


Now, we both knew there was a clog in the system, but I old him to go ahead and purge/recharge to see if it would clear up the problem. After the vacuum/recharge, we saw:

LOW PRESSURE SIDE is wayyyy too high (75 after just 1 can of R134a)

HIGH PRESSURE SIDE was basically normal


And now after this, I have no cool air, and my expansion valve is "hissing" when I turn the AC on. I know that sometimes they hiss when there is low refridgerant, which would make sense in this case, as we only added 1 can.

My compressor is fine. All electronics/sensors SEEM to be working fine.


My questions:

1. Do 240sx's clog Expansion Valves frequently? I plan to replace this.

2. Should I replace my Drier/Liquid tank with an OEM unit, or generic (Advance auto) unit? Is this necessary?

3. Is blowing compressed air through the system a bad idea? (due to moisture contamination). I would assume so, and I don't plan to, but I am just curious.

4. Has anyone encountered a similar problem.




Anyone with experience please chime in. Thanks.