A/C Charging - convert 3-port manifold to 4-port

[mthomas58]

While doing research on proper charging procedures, I ran across an interesting post on an A/C forum showing an easy DIY conversion of a std 3-port manifold to 4 using a small Grainger mini ball valve fitting (p/n#6GD44). The benefit is being able to completely purge the lines and manifold using a vacuum line while the refrigerant line is attached and ready to go. Purging the line itself by releasing a small amount of freon at the manifold connection may actually leave some residual air in the manifold itself.

As I understand things, the objective is to avoid introducing any air/moisture during the charging process and with the use of small cans, the risk of introducing air during charging is increased. I may give this a try unless the experts here state this is a waste of time. Total cost is a few bucks for the valve and hardware store fittings and $20 for an addl hose.

Stay tuned, my next innovation will be a DIY flush system using some misc HD plumbing dept items and a shop compressor. Tried flushing using a garden sprayer and could not get enough pressure to get a good stream of liquid through the unit.

[LM3929]

sub

[emac]

Mark

If you leave the line connected to the manifold and purge it as you connect you will not introduce any ambient air into the system. I must admit your set up it a great thought.

[3.2 CAB]

The additional line would need to be purged just like having the single source line would need purging. My method may appear to be too simple, but after I evacuate the system, I check to make sure that it holds the - pressures. Then before charging, after the tap is installed on the refrigerant source, I crack open the yellow source line then open the tap to purge whatever air might have been trapped in the hose, then I tighten the fitting and proceed with the charging. I know that the way that I have done, has worked on a/c systems since the very early 70's. I would think that the extra "new" line would still have to be purged at some point. But, it is still an interesting, in-expensive mod on the charge set.

[mthomas58]

Originally Posted by 3.2 CAB

The additional line would need to be purged just like having the single source line would need purging. My method may appear to be too simple, but after I evacuate the system, I check to make sure that it holds the - pressures. Then before charging, after the tap is installed on the refrigerant source, I crack open the yellow source line then open the tap to purge whatever air might have been trapped in the hose, then I tighten the fitting and proceed with the charging. I know that the way that I have done, has worked on a/c systems since the very early 70's. I would think that the extra "new" line would still have to be purged at some point. But, it is still an interesting, in-expensive mod on the charge set.

This is the point. In your method, you are not purging the air beyond the connection at the manifold. In this method, opening the refrigerant into a vacuumed line and manifold - there is no residual air - it's all refrigerant.

[mthomas58]

Mr Sims?

[tsuter]

How much residual air is left in the casting of the manifold? And how much moisture gets introduced by not being able to purge the actual casting when the yellow line is full of refrigerant and the other red and blue are still in vacuum?

I guess that's why someone designed 4-port manifolds????

[mthomas58]

Well, I was just out on ebay looking for an addl hose and found this with a built in shut off valve (eliminating the need for the Grainger valve) for $12.99

Better hurry, seller only has 16 left

[Jim Sims]

The EPA has been mandating the use of these types of hose rigs (which is why you found a ready made one). If fact, I believe the EPA only wants a few inches of refrigerant filled line vented ever. Professional/commercial shops can be inspected to ensure they are in compliance. Be aware that there are check valves to minimize venting of refrigerants to the air and to help prevent exposing the refrigerant cans/ cannisters to high side pressures if someone opens the manifold high pressure valve while connected to a system. These arrangements of check valves in some of the hose assemblies and in some of the can tap valves may trap minor pockets of air. The only way to completely avoid this is to open the can tap and vent some of the refrigerant out through a running vacuum pump. I don't think it is worth doing this for the minor amount of air purged. Another advantage of these hose rigs is they allow one to keep a partially used small can of refrigerant better sealed after opening (the can tap puncture needles don't always made a long term, tight seal) thereby conserving it.

[mthomas58]

Valved hose is in. Now I just need to pick up a one-in, two-out fitting to connect to the manifold.

Here are the instructions:

To use:
1)The valved center hose is connected to a vacuum pump.
2)The open port is connected to the refrigerant source (30-lb tank or can
tap set up on a can.)
3)The system is evacuated with both high and low side valves open.
4)Once vacuum is established for an appropriate length of time, the high
side is closed off, the vacuum valve is switched off and refrigerant added
to the system by opening the source (can or canister) valve.
5)Once the system is full, the source is shut off, and the low side valve is
closed.

If using cans, more than one can is usually needed. To switch cans use the
following:
1) The low side is valve is closed,
2)The can is switched, the new can is set up ready to go with tap valve
closed.
3)Vacuum the center section of the manifold by opening the vacuum valve with
with the vacuum pump running, wait for vacuum to be established.
4)Close the vacuum valve.
5)Open the can tap valve to pressurize lines.
6)Open the low-side valve to continue adding refrigerant.

[mthomas58]

Lucky me (for a change)! My Robinair guage set came with at T fitting allowing for two yellow hose connections without any further fitting modifications!