How do I read AC presssure tables

[jwakil]

I'm trying to recharge my R134 converted AC system on my 930, and keep getting confused by inconsistent tables. For example, on the can of R134 it says the low side pressure should be 35-40psi at 70F ambient. But if you look at this table its showing ~72psi at ~70F? FREON REPLACEMENT.
Is the temp in that table the ambient temp or is that the temp of the freon itself? What pressure is it giving?

[VW_NUTT]

What you are looking at is the refrigerant saturation table. In refrigeration we use it to calculate super heat coming out of the evap. With your suction pressure around 35 psig while running The saturation will be 40*F. I'm not in the auto A/C game but I assume the TX valve will be set for around 10*F, so if you were to measure the temperature of the suction line coming out of the evap you will read around 50*F. Your discharge air temp will also be around 50*F. They are just throwing in the 70* ambient so you are not trying to get 35-40 psig while charging the system on a cold day. If its 32*F outside you will never get there no matter how much refrigerant you dump in there.

[wwest]

The 72 PSI might be the 70F pressure one should expect with the high and low side equalized, compressor not having run for an extended period.

[Bob Kontak]

Originally Posted by jwakil

I'm trying to recharge my R134 converted AC system on my 930, and keep getting confused by inconsistent tables.

Lazy man's table.

Low side - around 40 plus or minus a few psi.

High side, twice ambient temp plus 50. 60F day - 120+50 = 170 psi.

Not perfect but within spitting distance of operating properly.

I have seen a stock 89 930 hit 425psi. Was an expansion valve issue. Edit - Not even sure why I said this but if you see 425, you are too high. :-)

[wwest]

Originally Posted by Bob Kontak

Lazy man's table.

Low side - around 40 plus or minus a few psi.

High side, twice ambient temp plus 50. 60F day - 120+50 = 170 psi.

Not perfect but within spitting distance of operating properly.

I have seen a stock 89 930 hit 425psi. Was an expansion valve issue. Edit - Not even sure why I said this but if you see 425, you are too high. :-)

"..expansion valve issue.." Or a few others might cause this...

Sticking thermostatic switch contacts, capillary tube "retracted" to much, loss of capillary tube gas, HOT rear lid condenser post HOT engine shutdown.

[wwest]

Originally Posted by Bob Kontak

Lazy man's table.

Low side - around 40 plus or minus a few psi.

High side, twice ambient temp plus 50. 60F day - 120+50 = 170 psi.

Not perfect but within spitting distance of operating properly.

I have seen a stock 89 930 hit 425psi. Was an expansion valve issue. Edit - Not even sure why I said this but if you see 425, you are too high. :-)

Hmmm.. "rumor" has it that the expansion valve never closes tightly enough to result in overpressures.

[SilberUrS6]

Originally Posted by Bob Kontak

Lazy man's table.

Low side - around 40 plus or minus a few psi.

High side, twice ambient temp plus 50. 60F day - 120+50 = 170 psi.

Not perfect but within spitting distance of operating properly.

I have seen a stock 89 930 hit 425psi. Was an expansion valve issue. Edit - Not even sure why I said this but if you see 425, you are too high. :-)

It appears our friend wwest is back. Is he committing AC disinformation again?