So it's only been 3 weeks since I recharged (after finding out from the mechanic that it's been retrofitted...) R134 into the system

Assuming he's done all the dye checks and leak sealing

Now my a/c isn't working. I feel no temp difference from Vent and Max cooling.
And I notice that the engine rev bobs up and down and correlate that with the compressor coming on and then off as in the video
http://www.youtube.com/watch?v=tNhaR6tLxP0

Is this acting normally? or did my mechanic miss a leak causing the AC to not cool anything.

 

if the compressor is contantly cycling its an indicator of low freon. it could have a slow leak and leaked out what you put in.

take it to a shop that was an AC machine and have them pull a vaccum on it. if it hold a contant vaccum for say an hour, then chances are its not leaking and it just wasnt filled enough.

 

After you recharged it, was it blowing cold then? And have you run it since then ?

 

That's cycling too quick. You have a leak somewhere.

 

Yeah, it did blow cold air, everything worked.
I told the mechanic to let me know if there was a leak, no reply, just got the car back and assumed it was a simple recharge.

Three weeks later I'm getting air no colder than on the VENT setting.

Definitely a leak then- Idk where though.

 

The shop "should" have put in some sort of dye to detect a leaky area. Even if they didn't, they usually have a leak detector probe. Sort of like a small metal detector, only it fits in your hand. They wave the wand over the system and where there is a leak, it will beep.

It could be something as simple as a leaky schrader valve. In that case, the car will hold a vacuum (since the valves are open with the hoses connected to the A/C service ports.) But once the hoses are removed, the schrader valves are supposed to stay closed, but may leak.