OK guys, on my 1991 Olds Toronado, I rebuilt almost the entire a/c system. new compressor, condenser, accumulator, orifice tube, new o-rings and seals. I took all the lines and hoses off the car and separately flushed each one. also flushed the evaporator core.
I got a new low side pressure switch but couldn't find any temp sensors, there is one for low side and one for high side. so I left the old ones in.
my problem is I can't get it to charge.
here'* what it does. gauges hooked up, freon connected to low side. low side gauge says 70psi. start car.
comp on, low side drops to 10psi
hi side goes up to 100
comp cycles off
low up to 80
hi side stays 100
comp on
low drops to 10psi
hi up to 125
comp off
low up to 80
hi 125
comp on
low up to 70
hi up to 150
then the comp won't come back on and dash says "refrigerant very low".
put car into diagnostic mode and compressor ran continuously for about 3 or 4 min and got more freon into system (can emptied) . low side wouldn't get below 50 but hi side got up to 150 but no higher. got cold air out of vents but shut car off, think I might be freezing up evaporator.
outside air was 80F so low side should be about 40 to 45psi and hi should be about 210psi.
any thoughts?

Just checking: You evacuated the entire system until complete vacuum, right?

You need to keep a solid vacuum on that system for at least 2 hours before filling.

evacuated it and it went down to negative 25 pretty fast and stayed there. left pump on for 45 min. still at -25
turned pump off and it held vacuum. after 45 min the gauge was still at -25 so I charged it.

You need to vacuum it longer to be sure you have zero atmosphere or it will not like it. 2 hours is minimum when I did them. Some larger capacity systems would be 3 hours or even 4.

My god. No wonder why nobody likes you.

Just googled the snot out of it. The average time is 5-45 minutes.

pretty sure it was evacuated enough, and that I don't have a leak, but I'm going to check the pressures again tonight or tomorrow. to see if it held.
It took about 24oz of R134A already. maybe a little less than that and the system holds about 30 to 36 oz. I'll have to check to be positive.
not sure where to go from here. The compressor sounds good, nice and quiet. I may have a crimped or rolled o-ring on the orifice tube. either that or a bad compressor would cause symptoms like this. it'* just weird that the car shuts off the compressor and tells me I'm very low on refrigerant when there is way more than 10psi of pressure in it.

You should charge it with the minimum for the system.

I just lost a bunch of text I had typed so I tried to attach it.

<<<CathedralCub added attached text to post'* message body>>>

the manual says the system holds 2.375 lbs. which is 38 oz. correct me if I'm wrong.
no minimum mentioned. it doesn't matter. something is wrong. it should have pumped up the hi side consistently with the low side slowly going up and down with the on and off of the compressor; comp on, low drops slowly hi goes up slowly, comp off low goes up hi stays steady.
my hi is not rising much at all and much too slow and the low side drops like crazy when the comp kicks on.
unless someone has a better idea, i think it'* a bad o-ring at the orifice tube not holding back pressure so the evap core is getting flooded with liquid refrigerant OR I have a bad compressor which won't pump up and hold the pressure on the hi side.

just checked it again.
put it in diagnostic mode so compressor cycles normal. (won't shut off because of low refrigerant signal from sensor)
low side stayed at 70 psi and hi wouldn't go above 125.
The line going into the evap core is very cold but coming out is not cold at all.
also, when I shut the valve off on the freon can the pressure on the low side drops to 0 !!
I may take the orifice tube out and look at it and make sure the o-rings are ok.
I'll let you all know what I find.
I'm screwed if the compressor is bad. I bought it last year from rock auto and didn't get around to putting it in until now because I've had the front end all apart restoring stuff. It'* a 4 seasons compressor. I'm going to call them but I'm not optimistic they will do anything if the comp is bad. $450 in parts and $60 in R134A and no a/c. Damn!
100 degrees here Tue thru end of the week.