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You do not necessarily have to a high port to do anything on your '93 system providing you know a few things about the condition of the system.
First of all I need to say this disclaimer up front.....
I have never seen a '93's under the hood components per say. I only know of my '91 R-12 system of which I believe to be very similar especially in the refrigerant cycle.
Port fittings are probably different due to R-12 versus R-134 and the requirement not to mix them.
When pulling a vacuum it would be better and faster to pull from both sides of a system to remove the most air/moisture quickly from two directions but it is not crucial. The larger diameter factory low side valve allowed quick access to do both. The answer would be yes, the low side is fine.
By having a low side observation port, if there is a restricted orifice or other obstruction the low side pressure will not rise properly. It will always stay low like being under charged.
If the unit is over charged, the low side will always stay higher than normal. The gas will not have a place to go and will become bound up "flow" wise.
In "Either case" cooling efficiency will decrease!
The switch in the accumulator is a controller and frosting preventer. The low side port is for monitoring it too. It is a very important part.
The dryer desiccant is on the low side and the high side is only tubing today. This keep the orifice free of ice inside it. The desiccant screens will also trap particles but is a little late to protect the orifice from compressor particles. (:-(0
This enclosed package, I believe, started out as a GM/Delco design.
I first saw them on about a '75 Corvette. It was up behind and under the right wheel well. You could open them. He'll of a place to put that thing to have change out the desiccant from!
It still used a TXV though!
An ultra sonic sight glass was used to charge them. Almost a must IF it did not have a sight glass or IF you could not see it!
So, Knowing the condition of the system comes down to, if the system was left open/uncapped to the outside elements for any extended length of time. Rule of thumb is longer than a half hour.
In the case of a "wet" system a good long time on the vacuum pump is in order. In those cases I go around with a heat gun and warm up components. This will decrease the boiling off time to suck out excess moisture from tubing and even that "desiccant package" inside the accumulator.
Releasing small bursts or quantities of "gas only" into the system can help stir things up and move out contaminants too!
After cleaning and holding a vacuum ( pump off) for at least thirty minutes the unit can then be charged. A good indication that there is no vacuum leakage, except at the ports seals which are open and things have boiled out while under the vacuum. Ports can have bad pressure sealing. The back up reason for caps!
With a complete vacuum the entire weighed charge should go in. It will equalize over a few minutes as the orifice is large enough to pass gas easily, as it designed to throttle liquid.
The orifice is basically a shortened length version of a capillary tube type of operating pressure reducing device. It is a reason for the term, critical weight charging! This is a balanced quantity system.
Any knowledge needed for high side pressures readings has already been calculated into the weight. This saved them the cost of having that port.
Orifices are far cheaper to make than TXV's but there are critical rules to follow and one is weight charging!
A minor note about, an orifice tube device. It will provide a wider temperature range of operation and higher capacity over a capillary tube system. So they still can ship them "more or less" world wide with minor charging adjustment if any at all.
FYI,
Where as, you take the older capillary tube refrigerators are charged more to the climate they are shipped to.
Do not try to take a North American refrigerator to the tropics or vice versa, you may be very disappointed!
If you read the manuals of the new high efficiency refrigerators they are very big on telling you about not using it in a very hot or cold garage! A Very tight band of range now or kiss it good bye working correctly and with cheapness! Better insulation, Smaller motors and calculated to a Nat's butt!
Anyhow, enough with spilling thoughts.
Wish you happy cooling soon!
Phil
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