Got the all the ac stuff back together & everything seems to be working fine. It seems some ac tech's use a scale and some go by the ac gauge's when filling the refrigerant. I went by the gauges. The specks call for 38.50oz. I have 36oz in there now, maybe a tad less. My center vent temp is 40F and low gauge swings from 40 to 20 and the high gauge goes up to about 150. The outside temp is around 68F. I figure I'll wait until it gets in the 80F's outside, see what the high side reads.
Anyway, my point/question is, using UNDER the speck 38.50oz OK ? Since everything (the gauges & center vent numbers) seems to be cooling using less frig

 

Don't know about Jaguar. In the case of my Alfa 164, my mechanic's advice is that, for older cars, avoid full fill-up as it might strain the system especially the ac condenser whose effectiveness might have diminished due to aging.

 

In the mid 90's, Ford's charge-labels were habitually about 2-2.5 oz above the "ideal system charge" as seen on the graph from the charge determination test. This gave a bit of cushion against intermittent small leaks, as the "Springloc valves...er "fittings"" they were using at the time were prone to exhibit.
Whether that methodology had made it over to Jaguar or not at that point in their ownership, I couldn't say. In any event, there is a fairly generous range above the ideal charge point before anything untoward happens, somewhat less so below the charge point. Personally, I would always fudge a bit to the high-side for that reason.

However, your numbers look good, so I imagine you are fine. I am dubious that one ever gets the full 12 oz from a can into the system, so beware you may really have 34.5-35 oz in there. I am a bit concerned about suction pressure of 20 psi. A rule of thumb is that evap temp (in deg F) is roughly equal to suction pressure (in psi) so you may have the beginnings of coil frosting/freezing which is indicative of a level of undercharging just below spec but above that which would cause rapid compressor clutch cycling. 80+ ambient and some high-humidity will reveal that soon enough, if it is, in fact the case.

Qvhk, your mechanic has me puzzled. Condenser effectiveness is solely a function of the cleanliness and condition of the tube-n-fin pack. That is, of course, assuming you've not had a compressor grenade in the system nor a dessicant bag let loose and clog things up. No moving parts, a sealing system at the inlet and outlet. Vibration-induced fatigue may have weakened a spot or two on it, which increased head pressure may exploit, I suppose...but in that case, you are on borrowed time anyway....like the automatic transmission that is working fine on all the sludge fluid but goes to pot when refreshed with new. Even so, R134a systems have a high-pressure switch to disengage the compressor somewhere above 350-450 psi, a pressure relief valve on the compressor set something above that value, and the condensers, when new, will sustain 3x-4x that or more before rupturing, so I'm dubious of his concern for the condenser.

 

I left out the info: It's a 95, 4.0, VDP with 134a refrig. I replaced with new Denso compressor (7.50oz total oil in system) condenser & rubber mounts, dryer, hoses and o rings. Vacuumed over an hour so the system held -28lbs low gauge -0 high gauge for over an hour, charged with 36oz of 134a, no leaks. Reason for replacing everything was compressor oil leak and age. Sorry, this info should have started the above thread.

 

Maybe it is just the old Alfa tricks. I had moments of the ac getting too cold leading to the system automatically cutting out to prevent freezing - the effect is loss of cold air momentarily before the system resumes producing ice cold air. The Alfa 164 factory original condenser is very small, and we can have dead slow traffic in the summer heat that may last till late November, so the mechanic's wisdom is not to over-stretch the ac system. Another local Alfa specialist told me the same. The efficiency of the Alfa ac system largely depends on heat dissipation through the condenser.

 

Wouldn't output air temp at the center vent approaching 32F freeze up your evaporator so depending on the accuracy of your thermometer 40F in my opinion be approaching the optimum .

 

If you are checking it when it is 68 degrees out the high side will shoot up when the outside temperature does,normally when it is hot out the a/c will work at 20 degrees cooler then outside temps.

If you put the premeasured amount in without totally flushing the system you may still have had refrigerant still in its oil form sitting inside which will then be converted to the gas form.

The premesured amount is for a totally empty system,so it is better to start out a bit shy,also if the car is hot while adding freon then the high side will increase and pressures will drop when driving as the airflow pulls more heat out.

Strangly enough on my 97 when the freon gets low and testing at the center vent the left grill or drivers side will blow colder then the passenger side.

I would keep the pressures a bit shy and recheck when the outside temps rise and the system is really having to work,that is when it will reach max pressures.