A/C Sight Glass?

Do modern vehicles have sight glasses on the receiver/dryer or at least the liquid line? My 1996 Toyota still does.

no, most do not. They expect you to use a gauge for accuracy. This said, manifold gauge sets do have a sight glass.

I might add that some current construction equipment still uses a sight glass

I see less and less of them. They’re not quite as useful on cars made since the mid 90’s.

My 2003 Camry has one. Just used it the other day as a point of verification in addition to the gauge reading…

I have seen those sight glasses in the gauge set. It looks like it visualizes the flow quality of the CHARGE line. How could you get the sight glass to visualize the liquid line flow? You would have to get the flow going from the high side hose to the low side hose i.e. in series with the liquid line.

In my research I have come to realize that the receiver dryer is being dropped: the charge amounts are dropping significantly;; and that slugging of the compressor is more of risk. If the system runs low on refrigerant the oil collects in the evaporator. If the system is overfilled with refrigerant or oil, the compressor is at risk for slugging.

Gone are the days of throwing a can of refrigerant and a can of oil into a system and calling it good.

Easy, when it’s low on refrigerant, there are entrained bubbles that are easily visible through the sight glass.
The sight glass I am referring to is part of the vehicle’s AC system.
I watch both the gauge on the diagnostic set and the sight glass. The pressure reaching acceptable range on the gauge coincides with elimination of bubbles seen in the sight glass…

you do not want to open both valves, high and low side, at the same time when charging your a/c. Only the low side should be opened and the high side closed. As a matter of fact I do not even connect the high side to avoid accidentally having both sides open. The bubbles you see in the sigh glass are produced by the flow of refrigerants through the gauge set, sight glass, and then to the a/c system through the low side connection.

Frankly, as a DYIer and to only top off the a/c with refrigerants, a can with a gauge will do just fine.

So this only works while filling, right? So it’s not a substitute for a sight glass in the system.

the sigh glass in your car, if it has one, servers the same purpose as a sight glass in a manifold gauge set. No difference whatsoever.

The sight glass is to view the liquid line and when operating properly fully charged there should only be liquid, i.e. no bubbles of vapor visible. Also, if air is left in the system it will appear as bubbles regardless of the pressure and level of charge.

The sight glass on a charging manifold will rarely run clear and then only when charging liquid.

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It would seem to me that one will always see bubbles as the liquid propellant turns into gasses as it is introduced into the system. That’s why it goes into the low side.

And that’s why the sight glass on the gauge will be different than the sight glass on the car.

I am not following, texases, why different? The car’s sight glass is on the low side.

No, the car’s sight glass is on the liquid line which is the high side between the condensor and the expansion valve.

It’s generally recommended that a few bubbles remain in the sight glass if that is being used to charge the system.
That will allow for a bit of heat related refrigerant expansion.

And to reiterate about what was mentioned earlier; never, ever open the high side of the gauge set when a can of refrigerant is tapped and open.
I’ve seen a few blow up and it’s not pretty along with being very dangerous.

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The car’s sight glass is never on the low side. It’s always on the liquid leg of the high side.

The sight glass on the gauge set you hook up to a car is useless for determining charge. There’s no refrigerant flowing through it when the system is running.


I stand corrected, thanks. You are, of course, correct.

I don’t use tiny cans of refrigerant but all the cans today come with a check valve. Back in the day if you had a can with a black valve there wasn’t a check valve so you could shoot some refrigerant back into the can. No, you shouldn’t do that, but as long as you have a small piece of brain intact you should be ok. Christ, now a days they have warnings on shampoo saying don’t eat it. I’m afraid of what this world will be like in another 50 years.

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Remember the movie “Idiocracy”? Originally made as a comedy, it is rapidly becoming a documentary of what we will be like in the not-too-distant future.