air conditioning related overheating

[Andrew <aos+yahoo@xxxx>]

Hi group. I've recently developed a sporadic overheating problem. It may 
have been around longer, but since it appears to be related to the only 
recently fixed air conditioning, it's only recently popped up.

Most of the time, I'm just fine. If the AC is off, my temperature gauge 
is solid on the first line above the bottom and does not fluctuate at all. 
If I turn on the AC, it'll move up above that line just a little, but no 
more than I would expect with the additional load and heat dissipation.

But every now and then, particularly if I've been sitting still, I'll look 
down and find the gauge has creeped up into the red zone. Here's the 
funny part, though. If I turn off the AC, the gauge will drop back to 
normal within seconds. If I turn the AC back on at that point, I'm 
usually fine again, although after a while (and a few more stops), it may 
start to creep up again.

This car has persistent low voltage at idle problems, but I don't think 
bad enough to cause enough slowdown of the cooling fans to cause this kind 
of a problem. I am fairly certain the cooling fans are running when they 
should be, although since this problem only pops up when the AC is 
running, I can't easily hear them. I have checked the breaker to make 
sure it's the upgraded 40 A.

I'm going to be replacing my steering rack this weekend, and will check 
all the usual suspects for cooling problems... thermostat, otterstat, air 
in the system, etc., but I'd like to know if anyone has any specific 
ideas, given the apparent relationship to my air conditioning (which is 
filled with R134a, FWIW).

As a side note, #4115 just rolled over 50,000 miles the other day. It 
actually went over 50K at least a couple of thousand miles ago, because I 
know the angle drive was broken for its trip here from California, and who 
knows how much more of its former life, but we'll pretend those miles 
don't exist.

Thanks.

-andrew
#4115
Houston TX