The AC wasn't blowing cold so I took it apart, replaced the drier and put a vacuum on it for an hour and put some refrigerant back in. How much refrigerant? About 38 ounces worth.

Here's my problem...

I can't get the needles on the manifold to switch on and off! It's 86F (30C) outside today. The air blowing is 55F (13C). The low pressure needle eventually pins itself at around 45psi, and the high side is up to 325psi! What am I doing wrong? The window in the drier looks good. Pics attached.

If I hit the gas, the low side pressure does drop and the high side goes higher. Once I take my foot off the gas, it goes back to the 45/325 readings.

The picture with the low side higher than the high side is when the AC is off.

 

You have to check pressures when the AC system is running and you check one side at a time. (Do not check both low and hi sides at the same time!)

85 degrees ambient you should have 45 - 55psi on lower side (which you do) and 225 - 250 psi on the high side (which you don't)

Two things, you could be slightly overcharged or your expansion valve or orfice tube could be blocked. Orfice easy & hope it's not the expansion valve.

55 deg output actually not terrible for 85 degrees ambient. Will probably come down further once you figure out why your high side is "higher than normal".

Again, check pressures while system is running. Pressures with system off will naturally be higher.

Also, what year car and also freon should be added by weight...

 

1996 XJS, I added about 38oz of r134a. No additives. (Well, I did add about 25ml of PAG100 oil) I understand adding by weight, it's just that the readings seemed way high...on the high side. I was expecting numbers in the 225 range.

When you say do not check both low and hi at the same time, I suppose that means only open on valve at any one time? With both valves closed at the manifold, both valves were open at the car's schraeder valves.

A few years ago, I did replace the condenser, as well as the expansion valve. Expansion valve, while a little difficult to get to, not a difficult job.




AC on, car idling.



Drier window looks right...



Direction of drier. Did I somehow reverse this?



What the manifold looks like with the AC off and car idling.

 

Whatever I did wrong seemed to even itself out. I fired up the car this morning, it was already 89F outside and after revving the ending and hosing the condenser down, it was clear everything was low. The high side was at 150psi and the low side was hanging out at 35.

pumped in some more refrigerant until the low side started to click off at 45psi and the high side clicked off at 225psi. Air is coming in at 48F when driving. I think I'm done?

 

Yep, all done! Those pressures are spot on!