The advantage of having a 4-port manifold is to be able to utilize a vacuum
pump to remove non-condensible gases from the refrigeration system AND the
manifold lines before and during the system charging process, instead of
relying on manifold line purging. Line purging is incomplete at best due to
gases trapped in the manifold itself.
This article is for those who already have a three port manifold who want to
inexpensively upgrade to a 4-port system. This conversion is pretty simple.
It does not have quite the flexibility (or performance) of a commercial
4-port manifold, but it ain't bad either.
A picture (included) is probably worth a thousand words, but basically by
teeing in an additional, valved port in the vacuum/fill line you can achieve
the benefits of a 4-port manifold. I used a small ball valve available from
Grainger (part 6GD44 for $3.46,) some 1/8 inch pipe fittings from Ace
Hardware, and an additional flexible refrigeration hose. So, for about $20
I have converted my refrigerant manifold to a 4-port system. The valve I
have used is particularly good for this application, having good open flow
characteristics as well as very low leakage when shut off.
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
If using cans, more than one can is usually needed. To switch cans use the
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
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.
Summary: I like my 4-port commercial R134a manifold better. It has better
flow at high vacuum with an oversize manifold body and a 3/16 vacuum line.
But for my money, I'm plenty happy with this setup for my R12 and R22
systems. It would be possible to add a second valve for the refrigerant
source line like a commercial manifold would have, but by following the
above procedure it is unnecessary.
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