Pulling an A/C System Vacuum - PeachParts Mercedes-Benz Forum

Ken300D · #1 06-02-2009, 05:58 PM

I will soon start on my 300SD A/C system work.

I have a good pump.

Will I need some sort of hard line from the pump to the A/C system port? Something that won't collapse under vacuum? Know of a source?

Thanks,
Ken300D

slk230red · #2 06-02-2009, 06:04 PM

Quote:

Originally Posted by Ken300D

I will soon start on my 300SD A/C system work.

I have a good pump.

Will I need some sort of hard line from the pump to the A/C system port? Something that won't collapse under vacuum? Know of a source?

Thanks,
Ken300D

I just connect my vacuum pump to the gauge manifold so I can read the vacuum. After sufficient vacuum time, shut off the valves, disconnect the hose from the vacuum pump, connect the freon, charge the system.

Matt L · #3 06-02-2009, 09:19 PM

Why do you need a hard line? Why not a simple lowly AC service hose?

gmercoleza · #4 06-02-2009, 09:22 PM

Just use the center hose from the manifold gauges, no need for a hard line.

dannym · #5 06-03-2009, 07:58 AM

Quote:

Originally Posted by slk230red

I just connect my vacuum pump to the gauge manifold so I can read the vacuum. After sufficient vacuum time, shut off the valves, disconnect the hose from the vacuum pump, connect the freon, charge the system.

Your allowing air into your system without purging your lines.

I just use a regular hose to the center port of the gauges. Never had any problems with hoses collapsing.

Danny

slk230red · #6 06-03-2009, 09:20 AM

Quote:

Originally Posted by slk230red

I just connect my vacuum pump to the gauge manifold so I can read the vacuum. After sufficient vacuum time, shut off the valves, disconnect the hose from the vacuum pump, connect the freon, charge the system.

Quote:

Originally Posted by dannym

Your allowing air into your system without purging your lines.

I just use a regular hose to the center port of the gauges. Never had any problems with hoses collapsing.

Danny

What? How is that? I connect the center hose of my gauges to my vacuum pump. After I finish vacuuming the system, I shut off the valves while maintaining vacuum, remove the hose from the vacuum pump, attach it to my freon jug, open freon valve, slightly crack the connection at the low side to allow freon to push out air in line.
Charge system, check for leaks, done!

leathermang · #7 06-03-2009, 09:21 AM

They knew those hoses needed to withstand pressure in both directions..

As to purging the lines... that is the proper procedure.... but sometimes hard with the new ( self sealing ) ends mandated on some hoses... I would like to know how to purge them if someone knows... without freezing the end of a finger of course... Do you have to make some jig for this procedure ? I can imagine one.... but hope someone has a better way than having to make one...

TX76513 · #8 06-03-2009, 09:27 AM

Quote:

Originally Posted by leathermang

They knew those hoses needed to withstand pressure in both directions..

As to purging the lines... that is the proper procedure.... but sometimes hard with the new ( self sealing ) ends mandated on some hoses... I would like to know how to purge them if someone knows... without freezing the end of a finger of course... Do you have to make some jig for this procedure ? I can imagine one.... but hope someone has a better way than having to make one...

Push the "Purge Lines Button" on machine

leathermang · #9 06-03-2009, 09:30 AM

Quote:

Originally Posted by slk230red

What? How is that? I connect the center hose of my gauges to my vacuum pump. After I finish vacuuming the system, I shut off the valves while maintaining vacuum, remove the hose from the vacuum pump, attach it to my freon jug, open freon valve, slightly crack the connection at the low side to allow freon to push out air in line.
Charge system, check for leaks, done!

Another recommended procedure .... particularly if you do not have the equipment to recover your freon in case of a leak....

Is to charge the system with nitrogen and four ounces of R22 as allowed by the EPA guides.... that way in case there is a leak you can legally vent that and fix the leak , re vacuum and charge system ,check for leaks again and be done with it... most people do not have an actual recovery tank but might could rent or borrow a bottle of nitrogen...

leathermang · #10 06-03-2009, 09:32 AM

Quote:

Originally Posted by TX76513

Push the "Purge Lines Button" on machine

It seems that I need new glasses...can you describe how to find it by braille ?
Thanks,

Matt L · #11 06-03-2009, 10:36 AM

For purging a line with self-sealing connections, I screw the hose onto an unused fitting until it just cracks. Hold that end up, as air is lighter than refrigerant, and slowly let the air out. It is obvious when you are out of air and into refrigerant, as the tone of the hiss greatly changes.

leathermang · #12 06-03-2009, 10:40 AM

Thanks Matt, where exactly is that ' unused fitting' ? Where did you get it ?

dannym · #13 06-03-2009, 10:52 AM

Quote:

Originally Posted by slk230red

What?.....slightly crack the connection at the low side to allow freon to push out air in line.....

You didn't mention that the first time.

If you pull a vacuum and disconnect the hose you let air in. If you don't purge it out the air enters the system.
Air in system is bad!

Danny

leathermang · #14 06-03-2009, 10:58 AM

I started to post the same objection... but decided that if he actually completely disconnected at the low side, then purged the line to there and reconnected it would be ok... but the more reasonable thing would be since the vacuum is all the way to the gauge to purge at the gauge from the freon tank then connect up tight...and connect to the vacuumed line from the low side to the manifold gauge set....

Matt L · #15 06-03-2009, 11:02 AM

Quote:

Originally Posted by leathermang

Thanks Matt, where exactly is that ' unused fitting' ? Where did you get it ?

I use a 1/4FL to 1/2ACME adapter, usually. I have a couple of those lying about. Of course, if it's a 1/4" fitting, I use a 1/4"M - 1/2F adapter, similarly for a 1/2" fitting. All the big names (Mastercool, Robinair, FJC, etc, etc) sell these adapters for a couple of bucks each.