If your AC is blowing hot air because of a defective heater control valve just disconnect the auxiliary water pump on the V8 and problem solved. My Jag was blowing hot air and when I disconnected the electrical plug to the auxiliary water pump my vent temp was 62 to 65F with the outside temp of 87F

 

Risks of engine overheat...

 

+1 on that!

The AC duct temperature you posted is pretty dismal. You should have a nice practically limitless supply of 38F air feeding into the cabin. With a properly operating system, if you were a penguin smuggler, and could understand their unique language, they'd be complaining because they're cold. All you've done is make the AC performance slightly less bad.

Disabling the V8 aux coolant pump is not a good idea, especially in hot weather. This excerpt from the training manual explains when it operates:



In a nutshell, in addition to improving heater performance at low engine RPM, the pump also kicks in automatically under certain conditions if the coolant temp is too high. I'd STRONGLY suggest reconnecting the plug and fixing the climate control system. You would once again have engine overheat protection and frosty AC performance. Troubleshooting guide here:

https://www.jaguarforums.com/forum/s...ol-how-185002/


Also, I'm not entirely convinced that disabling the pump would drop the AC duct temperature all that much. Per the training manual excerpt shown above, the pump is already switched off when a low cabin temperature is requested. For normal operation, this pump only runs when heat is requested.

 

Hello Karl,
The repair manual for my 2002 Corvette specs a vent temp of 50 to 52F at an outside temp of 86F (see chart below) so I though my Jag vent temp of 65F was not too bad for a quick fix. I do not have the specs for the Jag ac vent temp but you said it should be 38F. Where did you get this data from?
Howard

 

Wow, those Corvette specs strike me as somewhat pathetic. Seems to have a poorly designed system. Are those numbers specified with the vehicle not in motion, and thus minimum airflow (fan only) through the condenser? I would certainly hope any car could do better than that at freeway speeds, but if that's what Chevrolet says was good...

As far as Jaguar, I don't have any actual specs. In fact, I've never really looked but I'm sure they are out there. The 38F value I gave was based solely on my experience with my S-Type and other vehicles. That seems to be the value the designers aim for, to keep the evaporator from icing up. 38F seems to be the ideal margin above freezing for best AC performance, but without ice accumulation. This 38F setting isn't adjustable on our cars. My old pickup (1984 Ford, converted to R134a) is another story, and it uses an adjustable pressure switch to control evaporator temperature. I've experimented with that and if I get the duct temperature below 38F, the evaporator will slowly ice up and cooling output decreases. When the switch is adjusted to maintain 38F output, the cabin gets colder than Nancy Pelosi's heart.

I've done nothing special with the AC system in my S-Type, and it will freeze you out of the cabin even on the hottest days. I sure wouldn't settle for 65F.

I should also mention I keep that little pocket thermometer in the vent at all times. This helps me keep an eye on AC performance. When I see the needle down around 40F, I know all is good. If it creeps up, then I know the system may need some love. If the vent temperature was up around 50F (when commanded cooler), it would still feel cold and so I might miss this early warning. I might not be able to discern that difference, but the thermometer sure can.