MACS Service Reports - 2016 - JUN7

Paul Weissler
Paul Weissler

Figure 14: Close-up shows the two sensors were within 0.2 degree of each
other, very accurate.

most circumstances you hopefully will find are sufficiently
close. (FIG. 13, 14).
We'll close with some strictly anecdotal reports of condenser temperature drops approaching 100 F, and the system producing normal cooling from the A/C registers. If there was
enough sub-cooling, if the ambient was low enough and the
compressor was at 100% displacement, and perhaps even
the IHX factoring into the numbers, well maybe, but just
maybe. But a restricted condenser sounds more likely. ■

Figure 13: Simple check of the clamp-type temperature sensors-- just
clamp them together.

Many shops have the clamp-on contact digital thermometers, which come in a set of two and make a solid connection
to the refrigerant lines, so they're our preferred choice. However, here again you should check the two simultaneously
at the same location to see how they compare, which under

EVERYTHING STARTED OUT WELL
The 1999 Jeep Grand Cherokee with the 4.7-liter V8 came
in with the usual complaint: poor cooling. In fact the shop
could hardly find any cooling effect at all, so it took pressure
readings. Pretty much zero on both sides, and the current
owner hadn't reported any recent service, so the logical conclusion is that maybe it's just normal refrigerant loss from an
old vehicle. A small charge and probing with an electronic
detector didn't show any obvious leakage points, but it's an
old vehicle and it has a variable orifice valve (VOV) system.
Seems like a straightforward situation: recharge the sys-

tem and see how it performs. But first, let's review that VOV
(FIG. 15).

Chrysler's VOV explained

techauthority.com

If you're not familiar with (or more likely don't remember)
this design, it has two orifices that are parallel. One is fixed, one
variable and the VOV is built into the liquid line --you have to
cut open the liquid line for inspection. Yes, it would be possible
to splice in a replacement, and Santech does make a VOV available, but you'd have to also get a splice-in holder for a conven

Figure 15: Cutaway look at the Chrysler Variable Orifice Valve ("VOV"). It has two orifices, one controlled by a bi-metallic valve that responds to refrigerant temperature.

June 2016

7

MACS Service Reports



http://www.techauthority.com

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