That hole is probably used to evacuate any moisture from the drier upon completion of the manufacturing of the drier. Why is it there? Because that drier is a universal drier and could have been used on many applications, likely including one that has a pressure switch screwed directly into the drier. Replace the drier with an OEM or another universal that doesn't have the extra port for a pressure switch.

so do you know what the hole is for? - can I just plug it?

The drier looks original.
The nut with the hole is probably for the pressure relief valve, in case the pressure in the system exceeds a certain value the drier will vent off. The valve could be defunct.

1 can (12 or 16 oz) is not enough for your system.

Get a new drier, it does not matter if there is a nut on the T fitting, you can buy driers here on PP. Get 2 new orings. Put on the drier, evac, charge by P&T and anticipated weight. Search for leaks.

If you are buying small cans of R134a, avoid those with refrigerant oil, leak stop, enhancers, etc, just get pure refrigerant.


Next time, NEVER put sealant in the system otherwise you could be stripping it all down and spending a lot of time and money.

thanks for all the advice - I wound up tapping the small hole - tap would only thread in 3mm before hitting something - I put in a small bolt with sealer on the threads - so far no leakage - we'll see - this might all be moot though for two reasons - first: summer's about over here in Colorado (temps today in mid 70s) second: after talking it over with my son we're selling the car - he's back at school and didn't want to take the car with him - so instead of it sitting out covered in snow all winter we're going to sell it - it was his first car and I think he has moved past it - we enjoyed working on the car together and i think I taught him some of what I've picked up over the years - maybe he'll pick up another one in the future - at one time I had 4 of these cars - this is the last one left - it's going to be strange not seeing a 944 parked out front

I'd say your son made the right decision ;)

Sell it. You can always find another when you are in the mood.

Enjoy the rest of your summer.