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Understanding Static Pressures

MrDiedel on Sun September 15, 2013 2:53 PM User is offline

I've read some posts in this forum about static pressures. I would like to put in my understanding and have all you guys help create a fuller or more complete understanding for me. Please help me fill in the blanks and correct mistakes or add additional information.

*Static pressure should only be measured when the engine compartment (or area) surrounding the A/C system is at ambient temperature (or temperature in your shop) to ensure accuracy. This will prevent engine temperature, a hot sun, cold winds and etc. from changing the readings.

*Static Pressure is useful for determining if the system has other gasses in the A/C system other than the one specified for the system. For example air, nitrogen, or another type of refrigerant.

- If static pressure is too low, this could mean.....(help me fill in the blanks please)

-If static pressure is too high, this could mean you have a non-condense-able gas. (other conditions?)

*Static Pressure does not help you understand the state of charge in an A/C system because a 12oz can of R134a will have the same static pressure as a 30lb container.
(But is this true? If I filled a 2.5lb system with only 12oz, wouldn't the static pressure read low? I was under the impression that when the system had the correct weight of freon, it would also read the correct static pressure. Does a full 12oz can has the same static pressure as a half filled 30lb container?)

This is my current understanding and questions along with blanks. I welcome your additions/comments and or advice. Thanks,
Mr. Diedel

94RX-7 on Sun September 15, 2013 5:59 PM User is offline

Cussboy on Sun September 15, 2013 6:54 PM User is offline

When there is enough refrigerant present that some of it is present as a liquid, then the measured static pressure will be the same, regardless of how much liquid refrigerant is present.

So in general, static pressure is only really useful for determining if there is sufficient pressure to engage the low pressure switch of the AC system.

So the ambient temperature can affect the static pressure a little, thermodynamics laws.

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