A/C compressor not taking freon

[Jr2235]

I just replaced my ac compressor and my tensioner as the tensioner was seized. I made sure all lines were tight and that everything was connected. The compressor doesn't seem to be taking any freon. Obviously the clutch ins't going to engage with no freon in the system but what am I doing wrong. Should I jumper the pressure switch with a paper clip so that the clutch engages? It's a 2005 GMC Sierra 1500 with a 5.3 vortec if that helps. I would appreciate some help here thanks. 

[CamGTP]

You must vacuum down the entire AC system before you just add freon back in.

[davester]

...I believe you also need to add a specific amount of oil to the system in the right spot.  I would suggest taking it to a a/c so they can add both the right amount of oil and vacuum/add the corrtect amount freon to the system properly.

[Jr2235]

nope I don't let anyone work on my vehicles. but I will vacuum out the system and add the right amount of oil and freon.

[txab]

Why did you replace the compressor?

[davester]

Do you even know how much oil to add, or what kind of oil, or how much freon, or what kind of freon to use?  Do you have the tools to do this (ie, the cans with the pressure gauge on them are not what you need)? Did you do any research on how to do this?

[jgrote]

AC work is not difficult, but does require some special tools. You'll need a set of gauges. HF is fine for this. You'll need a vacuum pump. HF is fine for this too. Autozone by me will actually loan one out. Then you'll need to watch a bunch of YT videos to learn what all the numbers on the gauges mean. When you replaced your compressor, there should have been paperwork with it that said if there was oil in it already, and how much. There are resources for telling you how much you'll need to add based on what you're replacing. It's critically important you get this part right. Once the system is repaired and back together, put it on a vacuum for 15-30 minutes. Humidity is your enemy, so wetter climates need more time on a vacuum. Then, turn off all the valves and the pump, and mark the needles on your gauges. Now go and get some lunch. The longer you can let it sit with a vacuum in it, the better you'll know if there is a leak. Then fill with the appropriate amount of R134a. Now for the MOST important part. Be careful when buying your refrigerant. Some of them have oil added to them. Some have dyes. Some have stop leak. All that crap is terrible for your system. Get the right stuff, and use the right amounts. More is not better here. Same deal with the oil. There are many kinds. Get the right one. I'm new to these trucks, so I don't know what the right stuff is yet, but I've rebuilt enough AC systems to know what works, and what doesn't. Oh, and if your compressor grenaded, you'll need to flush the system out. And ALWAYS replace the dryer if the system has been empty for any amount of time, had a decent leak, or you live where there is any humidity.

 

Wow, my first post here turned into quite a rambling mess. Enjoy!

[Jr2235]

I fixed the problem it just ended up being a bad replacement compressor as I got it from a junkyard I bench tested the compressor and the clutch wasn't engaging. I went back to the junkyard and got another compressor and I bench tested that one and the clutch engaged. Put it on the truck and took the freon no problem and its blowing cold. Thanks for the help. 

[CamGTP]

Just be warned that if you didn't vacuum the system down you now have air/water trapped in the system that can hurt the compressor and corrode the inside of the system over time.

[sefiroxx]

You MUST vacuum the system down to
- confirm no leaks
- remove moisture from the system. Moisture can freeze into an ice block, creating high pressure and blowing the compressor

Proper vacuum will pull in enough Freon to clear the low pressure switch.

Start system. Meter in Freon until you achieve FSM spec.

You'll want to waTch the guages for extreme pressures so you can shut tHings off in case system is out of spec. Do

DO NOT use the quick fill small can adapter guages.

Also. Stop leak stuff is only short term and possibly damaging if too much is used. If it's in the system, the next time the system is opened, it can gum up the woeks preventing proper sealing when assembled. Requiresb chemical flush of components, rebuild of compressor and new bdrier (pieces of sealant floating around)