I was hoping someone would walk me through the A/C system charging process for my 95 850 GLT.

The system has no pressure right now so the low pressure switch near the firewall is protecting the pump and killing the power to the clutch. Do I need to jump this switch when I put the first can of refrigerant in so that the compressor will begin to build up the pressure and "move the refrigerant" through the system?

Is the port that I put the R-134 into toward the front of the car on the black, metal refrigerant line that runs from the top of the dryer all the way back to the firewall and has the low pressure switch mounted on it? It looks like a big valve stem for airing up a tire or something, has a cover on it that says "6nM Max." Isnt that where the R-134 is introduced into the system?

I have tested my pump by jumping the pressure switch for just a sec or 2 and it does work.

Thanks in advance for any help.

1995 850 GLT, non Turbo
220,000 miles

 

If you are asking this question you most likely should NOT jump that switch. The first can will go in it's just that you'll have a little bit of waste in that the can won't empty as much as it could. For maybe a buck or two of freon it's just safer not to jump that switch as you most likely will be changing cans and the pressure could be low enough in the system to cause damage to the compressor if it doesn't get oil flow on the rings on the pistons. There is a small chance it could happen if you end up taking too long to get the second can ready to inject. That's the whole reason the switch is there to begin with. Think of the last "easy" or "fast" job that should of been 15 minutes and it ended up taking ? hours.

Youtube it

Example of someone with limited knowledge doing their Volvo
How to refill ac in a volvo - YouTube

Doing one car is pretty much the same as any other car other than finding the low side port. On some cars they are pretty hidden. On an 850 it's pretty much out in the open you just have to be careful of getting your hose or hand too close to the serpentine belt. Start the car, AC on, Temp on max cold, fan on high and inject the first can until it's empty. Hook up second can and again let it go until it's empty. If you shake them you can feel the freon (liquid) in the can slosh around and you can tell when it's empty. The other way is it will feel cold as the freon is transferred and it will warm up to the touch when the transfer is over.
If you are buying the freon from a store DO NOT get the ones with the plastic connector as shown in the video above. The problem is you can only use their refill !! More $$$
Make sure you get one that will mate with the metal screw on threads on the top of the metal cans. That way you have choices on what brand, size or formula you want to buy. Also my personal recommendation is get one with a gauge. It helps you put the right amount in as too much can be as poor in performance as too little. It's also reusable next year and or in a week or month to monitor if you kept the charge or if it's leaking down.

Second photo is the style that will screw on to any ones replacement can.

 

Well, if your filling it you have a leak.

There will be a fat nozzle and a skinny nozzle. The fat is the low side the skinny is the high side. You can just charge it but it wont be as cold. You really should be pumping down your system to remove any moisture. Once its pumped down and you begin to introduce freon you can jump the pressure switch by the firewall to get things moving. Its not a good idea to run it unless there is oil in the system though so I am saying this because I am assuming that everything is alright and you just need freon. You may be just low and a small amount may trigger the pressure switch.

 

If they system as not been opened, you may be ok just adding freon. I don't know much about pressure switches and stuff like that but do get a service tool with a gauge on it. Also, if you don't know where the leak is, get the freon with the dye in it so you can chase the leak down. It's likely in the evaporator but if it holds a good charge for more than 30 days I wouldn't bother fixing/changing the evaporator. Not worth the time or $$$.

 

Getting a can with dye isn't a bad idea. You can use any black light source to get the dye to glow. From a simple black light bulb at the hardware store for posters to the handy flashlight style with enhancing glasses from an auto parts store like picture two, around 40 bucks. There is a chance you might see it without the black light but it's so much easier with it.

 

You can get the gogles & pin light for $10 - $15.

 

or a fifteen dollar one from autozone Part # 438. I have an electronic detector so I'm not recommending one over the other. Just giving some ideas on what, where and how much. If you want the cheapest you have to do some leg work of your own.