AC gauges, How do you read them?

The readings depend on many factors, most of all ambient temp, so it's hard to give exact values.

Typically on a cycling clutch system I'd expect low side to be in the 30's to mid 40's idling on a moderate day (70F-80F). If the AC system is in good shape it will eventually drop the low side below the cut-off (around 20 PSI) and the compressor cycles off for a bit. The high side will be fairly high with R134a unless you switched to a modern parallel flow condensor. 250-300 PSI is normal. With a parallel flow condensor the high side will be right at 200 PSI. Makes a big difference.

You also want to look at how the low side cycles. If the pressure drops rapidly until the compressor goes off, then pressure comes back up and drops rapidly again, you're under charged. If the pressure is up in the 50's or higher and never comes down, plus the high side is over 300 PSI, you're over charged.

PERFECT! That is exactly what I needed! Many many thanks!

Duder

A good rule of thumb for 134a

With windows open,
Inside fan on high,
selector on max (recirculate)
engine @ 1500 rpm,
evaporator fan on
High side psi should be about 2.5x the ambient outside temp in F degrees.

So at 85° the high side should be around 212psi.

Under no circumstances should the compressor be cold but the compressor suction alum tubing should be cool and/or sweating.

010752 said:

So at 85° the high side should be around 212psi.

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Sounds low for a C3 serpentine condensor. With a parallel flow, I'll buy it.

BTW, I recently swapped out my original condensor for a parallel flow unit and the highest it went after charging it was 190 PSI. With the old condensor it would go close to 300 by the time I put the last can in it.

zwede said:

Sounds low for a C3 serpentine condensor. With a parallel flow, I'll buy it.

BTW, I recently swapped out my original condensor for a parallel flow unit and the highest it went after charging it was 190 PSI. With the old condensor it would go close to 300 by the time I put the last can in it.

Click to expand...

I try to convince people to change the condenser, but there are a lot of "death kit" believers out there. :rolling:
What are your vent, dash pad and ambient temps at that pressure?

Believe it or not, on a flushed clean system, with a TUBE condenser, I've got as little as 240psi at 90+ temps. I'm a firm believer in as much condenser air flow as possible, whenever the a/c is on. It helps a lot.

I charged it on a 70 dgr day and it was blowing 41F out the center vent. I also measured it driving in traffic on a sunny 87F day and it blew 42F after a few minutes. I flipped it back to "AC Norm" as I was getting chilled. . But the big difference is that it cools off much faster after turning it on now.