Hello Everyone,

I have wonderful new-to-me 1984 300D. The previous owner took great care of the engine and everything else but there's some issues with the vacuum system that he ordered the parts for but never got around to.

Unfortunately, he never drove in Arizona during the summer so the A/C issue never came up.

I was hoping it just needed a charge, took it to the shop and had them test for charge and vacuum, all is well so they filled it with R134. The lines get cold, fan comes on, great stuff.

So the AC just blows super hot (read hotter than external air) no matter which switch I push. I've read elsewhere that people that couldn't get the right heat had a problem with the monovalve.

Now before I go digging around in the dash could this be a simple byproduct of the vacuum system or something else?

As of right now I have the parts to replace the ignition 3-way vacuum valve and the two rear door locks. I'm hoping that fixes it but if it is indeed the monovalve I'd love to hear an internet diagnosis so I can get the parts ordered.

Thank you!