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Trying to understand manifold gauges

befuddled on Tue July 15, 2008 6:01 PM User is offline

I was not so befuddled before I started looking at A/C manifold gauges. Maybe somebody can help me with some information on them.

Why can't any set of gauges be used with any refrigerant, assuming you have adaptors?

Why do some gauges have extra ports (5 as opposed to 3) on the ends? What are they used for?

Why do some gauges say not suitable for this or that particular refrigerant?

Why do some gauges advertised as R12/R134 have an extra set of hoses, and some don't?

Can a typical automotive set of gauges be used on a home air conditioner?

Thank you for your thoughts.

bearing01 on Tue July 15, 2008 6:22 PM User is offline

3 hoses
red-high side (compressor outlet) pressure
blue-low side (compressor inlet) pressure
yellow- charging or vacuuming.

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A pressure gauge is a pressure gauge. These gauges have two scales on them... one shows pressures and the other shows the temperature of the heat-saturated liquid in the system where the pressure is measured. If a gauge is for R12 then the temperature scale will be that of the R12 at the measured pressure. If R134a then a similar pressure reading will give a different temperature reading. Pressure is pressure, but the temperature scales are different for both gauges.

R12 gauges and R134a gauges have different standard types of hoses. R134a hoses have a black line running down its length.

You should have a gauge set dedicated to one type of refrigerant if you are frequently measuring different types of refrigerant. This is just to not cross-contaminate your refrigerant bottle or the system you are servicing. It doesn't take much R12 in an R134a system (or vice-versa) to make the system behave incorrectly. It also only requires a bit more than 2% one in the other to be considered contaminated.

Some gauges have a 3rd gauge. I haven't used one. I believe the 3rd gauge is for simultaneously measuring the evaporator pressure of a STV-POA type system while also simultaneously looking at compressor suction pressure.

Edited: Tue July 15, 2008 at 6:25 PM by bearing01

iceman2555 on Tue July 15, 2008 6:34 PM User is offlineView users profile

The two 'extra' ports on the end of the gauges are not ports...they are there to allow a location for attaching the service fittings to aid in their protection.

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