Posted by Chris Severance on May 19, 19100 at 20:24:16: via: n4-p55.modempool.com or 198.109.218.55
In Reply to: Warren - No reliable Venturi Pump Answers posted by Jamie on May 19, 19100 at 18:49:04:
I have the Robinair WW sells and it is sufficient and requires 75psi @ 4.5cfm. My 5HP compressor was just barely able to keep up with this. When I vac'd my system it took over an hour. Just imagine how much power this takes. Occasional DIY is fine but a shop couldn't ever afford the power costs or the replacement compressor parts. Get a fan to help keep your compressor cool or it will start making funny noises. The sound of the compressor pulling money from your pocket and delivering it to the compressor store is unnerving.
At 29.5" the flush started coming out. At 29.6" the water started coming out. The firs 29.0" takes no time at all. The last 0.7" takes a long time. I was working on an 80*F day with a warmed up car. Keep in mind that as the water boils off, the remainder cools and must wait to be warmed up to boil again. This is why vac'n takes so long. The motor vac pump will work at any temp and it can be left running as long as desired.
One bad thing about motor vac pumps is that their oil must be changed pretty often when vac'n dirty systems. Vac pump oil isn't cheap. It's too bad venturi vacs are so inefficient because it would be great to get out most of the grunge out with a venturi and clean up the minor remainder with a clean motor vac.
Venturi and single stage vacs cannot be used in the refrigeration industry because the high pressures and lack of dessicant make zero tolerance a necessity. MVAC works at lower pressures and a dessicant takes out whatever your vac leaves in.
>I am not going to pay another $150 to have my system evacuated again
>this crap it is like $60 an hour and it has to run for at least 2 or 3 hours
For $100 more you can have your own dual stage motor vac from Warren. When you are done send it to me and I'll pay for part. :) I want a motor vac, I just won't pay $289 for it.
It is also possible to rent motor vac pumps but I have yet to find out where. Autozone does NOT have them in my area.
You didn't discuss vac gauges. The pros like a Micron gauge which WW sells pretty cheap. I find that an engine vac/fuel gauge is fine. Just close off the system and run the vac. This shows you the maximum the pump will go. Then, start vac'n until the gauge reaches the same place.