Every can of refrigerant is a mixture of liquid and gas. R134a boils at approximately -15*F, so once the can is punctured and the internal pressure released, it immediately begins boiling.

If you hold the can right side up, it pulls gas into the system - if you hold it upside down, it pulls liquid into the system.

The concern with holding it upside down is the off-the-shelf cans charge through the suction line for the compressor, and the compressor is designed to pump gas, not liquid - too much liquid into the suction side of the compressor could potentially cause compressor damage.

That’s why professional grade AC equipment charges the bulk of the refrigerant through the high side - because that’s the side that’s meant to have liquid in it.

That said, if the system is already charged enough to run the compressor, the likelihood that too much liquid will be introduced into the compressor is relatively low, especially when using small cans.

 

I cannot disagree with you, Gumby22, but I suggest the low-side for people who have not used the high side for their safety. Perhaps that is what caused the explosion of a can of R-12 back when I was in Junior Collage, to the girl there. Thy didn't let us near the car, nor her. I dont wish to see anyone harmed by that at all. Even I simply use the low-side with a jumped low-side sensor to fill a vehicle up with R-134A. Do you understand?

 

I’m not trying to suggest using the high side without the proper equipment - just pointing out that the high side of the system is intended for liquid refrigerant, whereas the low side is intended for gas refrigerant - and why some people caution against holding the can upside down when charging.

All the off-the-shelf can adapters are made to connect to the low side port - they won’t fit on the high side. That was an intentional design choice by the aftermarket industry for safety and legal reasons.

I understand your method of filling the system - I’m not saying it’s wrong - but when starting with a completely empty system it needs to be done carefully to prevent compressor damage.

 

I don't disagree with you at all, Gumby22l. The R134A has to be slowly added on the low side by non-professionals.

 

Thanks to both of you for your expert advice on this subject. You guys have given me much education when dealing with the air conditioning of a vehicle. So yesterday I went ahead and jumped the cycling /low pressure switch to get the clutch to engage. I started to put one can of refrigerant in the system and after the first can was empty, and before I started the second can, I went ahead and removed the jumper from the switch and connected the switch back up. I than started to put in the second can in and within about 1 minute or so, the clutch engaged . At this point the low pressure came up to 30psi and the high side to 200psi. By the time the second can was empty, the readings were 45 on the low side and 250 on the high side. The ambient temp. was 90 degrees so according to a chart that I have here, thats about the correct readings. The temp probe in the center vents is at 40 degrees and it feels nice and cold. By the way, since I had replaced the condenser, I put 2 ounces of PaG 150 oil in the system. Hope it all stays nice and cold for a long time. Again, thanks to both of you because if you had not guided me in this project, I would of had to take the truck to a A C shop . Have a great day to all of you in this forum. Great bunch of talented people here.

 

Thanks, Birdman01.

We do our best to help Chevy folks to repair their cars. In this day and age, every penny counts. 40 degrees is great!