Automotive Air Conditioning Information Forum (Archives)

URDRWHO on Thu June 14, 2012 6:19 PM

Year: 1990
Make: Jaguar
Model: XJ6
Engine Size: 4.0
Refrigerant Type: 134a
Ambient Temp: 80
Pressure Low: 41 > 43
Pressure High: 190
Country of Origin: United States

I have always been under the impression that you should take ambient temperature readings at about 2 inches from the condenser. Someone told me today that it should be ambient surrounding the car. Who is correct?

Cussboy on Fri June 15, 2012 9:30 AM

I'd say that if your goal was to understand the operating pressures (or static pressure), then in front of the condenser would be appropriate.

But if you're trying to understand the temperature of the flow out the dash vents, then the air inside the vehicle (recirculate mode) or outside (vent mode) can both be involved.
For example, if the interior air (seats, dash, etc.) is 150F (Arizona, sitting in the sun), the air out the dash will absolutely NOT be as cool as it would be if the vehicle had been parked in the shade and the inside air is "only" 105F. The AC has to remove the heat from the air, ehich is getting heated up from the very hot interior, until equilibrium is reached.

URDRWHO on Fri June 15, 2012 10:51 AM

Operating pressures is what it was about and not inside the cabin temps.

I am always trying to get my inside cabin temps to the most efficient point possible. Years ago I changed from 12 to 134a and have never gotten it to the point of 12 and probably won't get there. Plus on the year of my 90 Jag and the 92 model, the engineers screwed things up. For some reason and who can ever guess why, the engineers didn't include a coolant cut off valve into the heater hose. So what happens is on a 95 degree day, with the AC on max, there will always be 180F coolant moving through the heater matrix. Ok, maybe on a bran new car with all vent flaps in perfect condition, it may work. But having that hot coolant under the dash will always want to weep out into the cabin.

The second problem is that these cars didn't have a fan that energizes when the AC is turned on. There is an extra fan that energizes at high temps but that is dependent on coolant temp.

Some people have added a coolant shut off (like my older Jag had) and they add a diode in an added circuit that will turn on the auxiliary fan when the AC is turned on.

It is 70 degrees outside. Cruising down to get a cup of coffee (35 mph two mile trip) my center vent blows 39>40. Get on the highway and it pulls down even more. With the same refrig in the car, when temps hit 90 outside, heading for coffee the center vent will blow about 50 ....maybe a bit higher and at idle it will be 60.

Yep pressures are what I was addressing.


Edited: Fri June 15, 2012 at 11:12 AM by URDRWHO

Cussboy on Fri June 15, 2012 2:15 PM

NAPA has a coolant shut-off valve. Or can you just bypass the heater core with the hoses for the summer?

Edit: converting to R134a is not always a slam dunk, and certain vehicles don't seem to convert well, from what I've read. I've never done a conversion myself, my import 1988 truck is still R-12.

Edited: Fri June 15, 2012 at 2:17 PM by Cussboy

URDRWHO on Fri June 15, 2012 9:18 PM

I was always sorry I switched to 12. I'm going to get certified so that I can buy 12. It is an easy verification test, a bit of study and ya got it.

I'll check out the NAPA thing. Thanks.