95 850 - A/C Evac, Jumpering, Engaging Clutch?

[jofinneg]

Even after reading the nice thread here, I am left with some questions:
https://www.matthewsvolvosite.com/forums ... =1&t=20392

Here is the situation re a/c (I'm fairly novice at this):

I had the old compressor freeze up on me on the highway and have now replaced it with a re-built unit.
The system was therefore completely empty of freon (R134a), and I went ahead and pulled a vacuum on system with a pump. The pressure is holding.
I connected the freon to the low port (under the computer module near the passenger side headlight) and then turned on the a/c from inside the car. The clutch did not engage.
I then took a paperclip and jumpered the sensor at the high side port (to verify the clutch actually was working). The clutch engaged, but I only let it run for a second, not wanting to damage anything.

So the questions are:
With the vacuum I've created, will the freon will go into the system without the compressor clutch engaged?
Do I need to jumper the high side sensor in order to engage the clutch while I am adding the freon?
Does engaging the clutch with an evacuated system risk damaging the compressor?
Do I need the type of R134a with the oil in it?

Thanks for your help.
John

[jblackburn]

You may be able to load up the system a little bit with R-134 without the compressor running. If the clutch will not engage even as you're loading refrigerant into the system, jumper the low pressure switch for 5-10 seconds at a time, then disengage it. Wait a few seconds and try again. Once you get 25 psi or so in there, it should run or at least cycle on its own with the switch plugged in.

[Bigblue]

This "advice" is given assuming that the system is still under a full vacuum...
Since you had to replace the compressor, and therefore lost any oil it might have contained, you should use R-134 that contains oil...The clutch will not engage until there is better than 40 pounds in the system, so you need to add R-134 until the pressure is at least that high...You will be adding the refrigerant (it is NOT freon) through the low side and the can should be upright so that the refrigerant enters as a vapor...The exception to this might be with refrigerant containing oil, the manufacturer might tell you to turn the can upside down so that oil is dispensed into the system...Make sure the compressor is not running when refrigerant is added this way...Liquid can "slug" the compressor and damage or destroy it...When you are adding the refrigerant, check to see what the outdoor temperature is and add refrigerant (system not running) until the pressure equals or slightly exceeds whatever the outside air temperature is...(90 degrees f =about 100psi)...If it will not rise to that pressure, put the can (upright) into hot water...The heat will cause the liquid to boil off in the can and pressurize the system some more...If you cannot attain the proper pressure even with the can heated, the can is probably empty and you need another can...Valve the can off and then shake the can to see if you can hear liquid sloshing around...If you don't, it is empty and you need another can...
As soon as this temperature/pressure relatuionship is reached, valve the can off and start the system...When valving the can off, do it while it is till in the hot water...If the can is removed from the hot water before tha valve is closed, the can will chill and the refrigerant will back up into the can...The compressor should run and the pressure should drop to about 35psi...Now you can top it off for optimum operation...

[jofinneg]

Thanks for these instructions- they are very, very helpful.

Since there is a vacuum, I assume the car does not need to be running when I do this (?).

I'll try this tonight.

Thanks,
John

[Bigblue]

No, do run it during this procedure...