AC system pressure

[MadDog]

I have looked around and while I can find a fair amount of info on the AC system, I am still looking for one piece of info:

What is the nominal steady-state low-side pressure supposed to be (assuming the freon is fully charged, Max AC is on all the way, 75 F outside temp) ?

thanks,

Mad Dog

 

[amc49]

A worthless number. For one, low side does NOT stay steady state, it cycles from 25 to around 50 psi. For two, it will do that through a whole range of highside pressures, which are what you charge to. Highside ranges from 200 psi to 300+, the lowside will be close to the same all through that wide range, why it's useless unless tied to a highside number. Why you cannot competently charge correctly using the lowside only. Of course they don't tell you that on the quickie charging kits.

You ALWAYS use the highside number to know when to quit charging, why the kits mess up so many cars.

 

[BrApple]

IIRC all of the 6 or so graphs that are used to determine if the AC system is correctly charged from the 95 Ford Shop Manual at 75 degrees the compressor will cycle and the low side pressure will not be constant. Its all dependent on a number of factors.

 

[MadDog]

I have the 2000 Service Repair Manual (same as Shop Manual ?) , and I have yet to find the AC graphs. I will keep looking.

So, if I understand correctly the high side pressure is mostly dependent on the charge, and not the operations ?

thanks,

Mad Dog

 

[BrApple]

My understanding is that all of the pressures depend on the charge.


So the pressure, ambient temperature and clutch cycle time all have to be taken into account to determine if the system is filled correctly .... of course this is after its taken to a vacuum and doesn't leak.