Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

test for you, skip all of this and try wiring things up so that the aux cooling fan comes on
whenever the compressor comes on. You can fake this by connecting the two wires at the temp
sensor up at the top right corner of the radiator (effectively bypassing the temp switch itself.)
Use a paper clip or something, wrap it with tape, close the hood and drive around and see if this
makes any difference. If this doesn't help I'm out of ideas.
If it does help somewhat (you'll obviously need some temp gauges to measure all this), there's
always the option of grafting the 780 aux cooling fan onto your 740. Volvo has a kit for this,
which I imagine is pretty pricey since it includes a brand new fan etc., but they needed it for
markets such as Arizona, even BEFORE going to 134a! As far as I remember the kit doesn't
include any of the logic suggested above, so I'm not sure it'll do anything unless some sort of A/
C triggering is added as well. [Editor] See Recharge Tips above.
Variable Orifice Valve Addition.
[Lee Fox] I wish I had heard about the variable orifice valve tubes before I converted. It sounds
like a good idea. You can find out about them at http://www.aircondition.com/vov/ This is also a
great site to learn all about automotive air conditioning. You can even take the test online to
become EPA certified to buy R12. In summary, I would recommend the conversion to anyone
who needs to fix an ailing AC. We be chillin'. [Chris Herbst] I've used several VOVs, and they
are worth the money, the time, and opening the system to put them in. The VOV does not
make a great difference on the highway, but in the city, under high transfer load, it does fantastic
work. Sometimes it can lower vent temps five degrees plus. R134 is not the best refrigerant; the
VOV makes the best use out of it. Also I believe that pressure-wise, it's better for the
compressor since there is better oil transfer and the compressor system doesn't get backed up
(too much heat to effectively transfer out between entering the condenser and exiting the
condenser). Opening the A/C system is not a problem. In fact, it won't hurt to purge the
system, add a little oil, recharge (and replace any or ALL available O-rings while you're at it) and
enjoy better cooling especially in the worst conditions. If you are in a very hot climate (like
Arizona or other areas where temps are routinely near 100 or more) get the VOV for high
temperature environments. It has a slightly different operating range for best results in those
conditions.
[Tips from A/C UPDATE: Retrofit Vs. Recharge, Retrofitting Techniques, Improving Cooling
Performance & Alternative Refrigerants, Larry Carley, ImportCar, May 2000 (Excerpts)]:
One way to improve cooling performance when retrofitting an older R-12 system to R-
134a is to install a "variable valve" orifice tube in place of the standard fixed orifice tube.
These aftermarket variable orifice tubes allow the flow rate through the valve to change
for better cooling at idle and low speeds. Such a valve can lower the A/C outlet air
temperature by as much as 5 to 8 degrees, which can make quite a difference if the
vehicle is crawling along in stop-and-go city traffic. Installing a larger or more efficient
condenser can also help compensate for losses in cooling efficiency with R-134a. If the
original condenser or evaporator is being replaced because of a leak, damage or defect,
make sure the replacement unit has the same or better BTU rating. Some aftermarket