Are you sure it uses 134A? It should have a label on it to tell you type and amount of ref, to use. I would also take it in and have it vacuumed out and charged, that way you don't have to guess. The compressor has to be running to draw ref. out of the can. If you don't see the compressor turning it won't work.
Well, for starters, if you haven't drawn the system to high vacuum, it will be full of NCG (non-condensable gas, ie: air), and moisture.
A vacuum pump & manifold gage set are pretty much a necessity for what you are trying to do here. You may be able to rent them locally. If you aren't sure how to use them safely, stop now & read-up on the subject or let a pro finish the job.
Unskilled use of the gage set while charging can cause refrigerant containers to explode & other annoying results.
The compressor must be running to draw the refrigerant in. I often put a dab of "White-Out" on the edge of the compressor clutch plate (NOT the pulley) so I can see at a glance if it is engaging.
Putting the can of 134a in warm NOT HOT water will help speed up the process. Keep the can upright so vapor, not liquid, goes in. This takes longer, but avoids the chance of compressor damage from a slug of liquid.
Find out your system capacity. Too much refrigerant can be more trouble than too little.
Hand & eye protection are swell ideas when doing these jobs.
Regards, Al.
I'm assuming the system was evacuated. Pumping R134A into an air filled system is not only dumb, it's dangerous, air can oxygenate R134A causing an unstable mix. My guess is a clogged orifice tube is preventing proper suction. Of great importance is, what type oil is system charged with ? Ester oil is used in conversions. PAG oil in new systems. Don't mix the two !
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