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Some Help Interpreting Some Line Pressure and Temperature Readings, Please

beady on Thu July 23, 2015 8:45 PM User is offline

Year: 2002
Make: Jaguar
Model: XJR
Engine Size: 4.0
Refrigerant Type: R134a
Ambient Temp: 94
Pressure Low: 55
Pressure High: 300
Country of Origin: United States

Hello all, I’m Mike from Virginia and I’ve got a 2002 Jaguar XJR that my compressor clutch bit the dust on. I replaced the compressor with a brand new Denso unit, new dryer, and new HNBR O-rings at the compressor and dryer joints I broke.

The place that evacuated my system before I did the work said they’d pull a vacuum and recharge it for $40, so I decided to go that route instead of borrowing my friend’s manifold set and vacuum pump and spending a couple hours out in the driveway in the 90’s figuring it out.

I’ll give you the background before I get to the problem:

So, I bring the car back to the shop, the guy pulls a vacuum for about 15 mins, shuts the machine off and checks the vacuum in about another 10-15 mins. It hasn’t dropped, so he goes ahead and starts recharging. Nothing is happening, and he figures out the charge bottle on the machine is empty. Hooks up a new bottle, sets up the machine and starts charging the system. I walk around the shop checking out the other cars and come back to the machine just before the guy does. The machine is showing it added 60 ounces. The charge should be about 25. He curses, then I lose track of exactly what he does. He said something about needing to pull a vacuum again, which the machine does for only a few minutes before he tries charging the system again. This time he sticks around and says the system is happily taking the charge. At this point I’m not sure if he discharged the whole 60 ounces, pulled a vacuum and put in fresh R134a, or just vented some down to get to the “right” charge and then pulled a vacuum for some reason before recharging…..

Anyway, all this was with the engine off, so I asked “does the engine need to be running?” So he says to go ahead and start it as he finishes up the charge. I look at the pressures and they seem pretty high; about 70 psi on the Low side and maybe 350 psi on the High side? I said “those pressures seem a bit high from what I read online about charging the system” and he said they would drop as soon as I started driving. The temperature in the shop was 100F by my car’s outside temp reading. Cool air was blowing from the ducts, but not cold. I drove the few miles home in 95F+ ambient temps, but the air never got cold.

Fast forward to the next day. I had my friend bring his manifold and gauges to work and we hooked them up to the car at lunch.

94F ambient, unshaded parking lot, heatsoaked car.

After letting car idle for 5-10 mins:

Lo side = 55 psig @ 85 F
Hi side = 300 psig @ 156 F cycling to 265 psig @ 153 F

Temps read with Fluke meter and thermocouple held onto refrigerant pipe with a wooden dowel at pressure tap locations.

Center vent on High fan speed, recirc on and windows up, temp bottomed out at 76 F.

I left thermocouple in center vent, fan on High and recirc on during my drive home. Once on the interstate at 60-70 mph and 95F ambient, vent air temperature eventually dropped all the way to 47-48 F. But, once I got off interstate and was on slow side streets and stopped at lights, the vent air temp quickly rose back to about 70 F and stayed there.

The next morning with temps in the upper 70’s or 80, with center fan on low and recirc off and on the interstate, temps stayed in the upper 40’s and car got cold enough I had to raise interior AC temp setting to low 70’s on the lowest fan setting.

So, I’d appreciate some help figuring out the state of my system before I go to a “real” AC place with a good reputation and pay more money. If it just needs a little more charge, I can do that with my friend’s manifold. Or maybe the TXV is stuck partially open which I’d fix myself before having the system recharged, or perhaps the guy left some air in the system….

Thanks for any help,


Edited: Thu July 23, 2015 at 8:46 PM by beady

Dougflas on Fri July 24, 2015 12:45 PM User is offline

If it were in my hands, I'd recover the charge, pull a decent vacuum and recharge by weight the factory amount of refrigerant. Then retest the system and record the readings.

beady on Sat July 25, 2015 11:51 AM User is offline

Dougflas, from my readings and description, and assuming the system was vacuumed correctly prior to charging, what do you think is the issue?

For the price of having the system recharged I can buy a decent manifold and gauge set and do the work myself, plus have the tools for later. I’m loathe to pay someone do what I can. I’ve done everything on all my cars for 15 years now except for alignment and inspection, I’d much rather buy the tools and get the system working myself.



beady on Tue July 28, 2015 6:59 PM User is offline


With full readings of vent, ambient, Hi and Lo line temperature readings, plus Hi and Lo pressure readings, no-one can tell me what this indicates?

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