1985 Silverado K30 R-12 Air Conditioning issue

[Chugalugg]

I've installed a new sanden style 7 piston series compressor, brackets, new manifold hose, dryer and flushed the evap and condenser. Hooked up my r-12 gauges, 20+yrs oldie usa made and new mastercool 3cfm vacuum pump and pumped on it for about 5 minutes, shut the switch off and lost vacuum immediatly. checked all my fittings and found one questionable gasket on my yellow hose so I replaced it with a new rubber.
Got it going again and the vent on the vacuum pump was misting for a minute then stopped. Let it vacuum for about 30 minutes and noticed the pump was VERY hot to the touch. shut it off and the yellow hose started shaking?? wtf? This is a brand new pump and new oil moved it to my bench and noticed that the oil sight glass was real low. I didnt smell or notice a problem in my garage the a/c window cooler was going so I was comfortable. Hope I didnt suck pump oil into a clean new system.
I've done a/c work off and on for 30 yrs never ran into this. I'm 99% sure I have a vacuum pump issue just thought I'd ask you guy for any advise. thank you for your time to reply.
chuck

 

[chengny]

Got it going again and the vent on the vacuum pump was misting for a minute then stopped. Let it vacuum for about 30 minutes and noticed the pump was VERY hot to the touch. shut it off and the yellow hose started shaking?? wtf? This is a brand new pump and new oil moved it to my bench and noticed that the oil sight glass was real low. I didnt smell or notice a problem in my garage the a/c window cooler was going so I was comfortable. Hope I didnt suck pump oil into a clean new system.

If you didn't notice any oil on the floor (from handle vent or shaft seal), it would be pretty safe to assume that; unfortunately, yes. The volume of oil you lost from the pump is now in the system.

But I wouldn't stress about it. That Mastercool pump only takes 8.5 ounces of oil. The 3 CFM JB Platinum pump that I use takes 28 oz. and a similar sized Robinair pump takes about 16 oz.

Point is - you still had at least some level showing in the glass, so how much could have been sucked out? I've never filled a MC pump, but I would guess that the volume of oil required to bring the level in the glass from a low (but still visible) level to the normal half glass operating level would be maybe...what a 1/2 oz?

Also, those MC pumps have a check valve in the suction line to prevent the backflow of pump oil into the system "in the event of a power failure". Since you didn't mention anything about a power failure...I am putting my money on a valve failure in the pump cartridge. The pump had pulled some degree of vacuum, then a valve got hung up. Now the system had more (or nearly the same) degree of vacuum that the pump was developing. When you saw the hose jumping, it was probably because the vacuum on either side of the check valve was equalizing - and it kept trying to close, but kept getting pulled open again.

Finally (assuming that you were evacuating through the low side service port) if you are really concerned about contaminating the system with the lost pump oil, it should have just dropped to the bottom of the filter/drier/accumulator. Installing a new one should ease your concerns.

 

[Chugalugg]

thank you very much for your time to reply. there was no oil on the outside of the vacuum pump but when i disconnected the yellow line from pump to dryer there was some oil. so, like you said the oil went somewhere and its probably in the dryer. hope it didnt go any further but other than starting from scratch how am I really going to know? Yes I was connected to the low and high side ports and used the proper mineral oil in each component before evacuating. btw, all the oil was in the old system was in the dryer. I didnt measure but left it upside down in my drain pan and there was a bunch of green oil. thanks again, chuck

 

[Chugalugg]

thank you very much for your time to reply. there was no oil on the outside of the vacuum pump but when i disconnected the yellow line from pump to dryer there was some oil. so, like you said the oil went somewhere and its probably in the dryer. hope it didnt go any further but other than starting from scratch how am I really going to know? Yes I was connected to the low and high side ports and used the proper mineral oil in each component before evacuating. btw, all the oil was in the old system was in the dryer. I didnt measure but left it upside down in my drain pan and there was a bunch of green oil. thanks again, chuck

oops, I got my colors wrong, red to high, blue to evap and yellow to vacuum pump to gauge set both valves open to evacuate.