Common leak points are:
-Hose connections
-Joints
-Sensor/switch hook-ups
-Front pump seal
-Pump body seals
-Charge ports
-Condenser
-Evaporator
First do a visual inspection of each of those items...except the evaporator...you can't really inspect that. Leaking that much refrigerant there should be an oily spot somewhere if it's leaking at a joint or the compressor. Take a flashlight and inspection mirror and look at each joint carefully. Give it a drink of refrigerant, run the tk. Then shut the tk off and right away take a spray bottle of
soapy water and spray the joints real good...and put a daub of soapy water across the charging ports...see if any bubbles form indicating leaks. There's a schraeder valve inside the charge ports and they could be goofed up or even just loose. Spray in to the condenser too. Look for bubbles forming. If you see bubbles then you're on to some leaks. You might multiple leaks...who knows?
If you live in the rust-belt, inspect the integrity of your tk's condenser in front of the radiator real good. Is it corroded under the paint (bubbling, etc)? When aluminum compressors leak, corrosion can migrate under the o-rings of the body, also leading to hard-to-spot leaks.
The most common leaks if you don't see any oily spots are probably going to be the charge ports and the front pump seal. That's the seal which goes around the compressor shaft. They're hard to ID behind the clutch, but leaking that much look for oil under the front of the compressor. You can actually replace that seal if you took it to an AC place. Or replace the compressor. It could very well be the front pump seal, esp with a lot of miles. But then again, it's possible the evaporator in the heater box is corroded too.
The best thing to do hones to god is to spend a few bucks & take it to an AC shop which has the right tools and pay to get diagnosis....even if you ultimately do the repair work yourself. Otherwise a guy could be chasing down a lot of leaks. You could put in some refrigerant with dye in it and use a UV flashlight at night ...that should show where the leak is. But $75 for a diagnosis might be cheap use of your time??? So you're not chasing expensive dead-ends.
If you are in the rust belt, and you believe it *is* the front pump seal, then you ought to replace the condenser and the accumulator because they're probably not too far behind in failing...due to corrosion. Do it all at once. Like I say, corrosion can get under condenser paint, and also under and around compressor main body O-rings. At that point I'd also replace all o-rings in the system. Make sure their seats are 100% super clean.
If you find it IS the evaporator (in the HVAC box), then you ought to replace the heater core too (since you have the dash out!). And again, if you are in the rust-belt, and your tk has a lot of miles on it, also replace the compressor front pump seal (or even the whole compressor) and the condenser and dryer. Because they're probably soon to fail anyway. And clean the expansion valve in case there's debris in it. Once new parts are installed, you need to use the proper oil (and right amt), then draw 3x deep-vacuum's to get *all* the moisture out before re-charging. Any moisture...even the smallest amt can cause ice to form at the expansion valve and cause it to freeze up (stop working). There's tons of videos on AC on Y/T....
Good luck!!
