I have two concurrent issues to touch on, but first, the specs:

1985 300D
Rollguy 7cyl Sanden retrofit, r134a
16x20 PF condenser
Everything north of the firewall is new, minus the aux fan which still works wonderfully
Evaporator hosed out, and video checked clean

Vent temps are near 55-60*F at their coldest
Ambient temps are 92-98*F

The readings below were taken after 10+ minutes of running at the mentioned speed, to let things stabilize, with a 48" fan on high blowing air through the front end.

At idle speed:
Suction pressure at 45psi
High pressure at 275psi
Vent temp 60*F
Condenser is at high high temperature to the touch, burn yo hand!

At highway speed (2000+rpm):
Suction pressure 30-32psi
High pressure 325psi
Vent temp 80*F+
Condenser cools slightly, its hot, but able to hold it for a few seconds.

First issue is the lowest vent temperature I've seen is 55*F...thats a bit warm compared to what I've seen from other retrofits posted in the forum.

Second issue is the loss of cooling at high speeds. No idea what causes it. I've read from other forums where its a clutch problem, its a low refrigerant problem, its a condenser problem. I have no clue.

My tiny brain suggests expansion valve, as that is the only part that was not replaced...then again, why does it work fine at idle (albeit with comparatively warm temps)? TxV stuck open maybe...but that wouldnt explain the drawdown of the suction side at high revs. It should stay reasonably close to the idle pressures.

Anybody have any good tips?

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1985 MBZ 300D (DD, 240k, unmuffled hellion!)
1982 MBZ 300D (372k, retired for parts)
1981 MBZ 300D (575k, parts pig)