[DML] Was: AC system compressor doesn't cycle, Now: AC pressure switch

["Marty Galbreath" <marty@xxxxxxxxxxxxxxxxx>]

Yes, I know all about the switch, I went through the "adjust it" 
then "don't adjust it" advice on the DML back in 2001 :) I eneded up 
buying a new switch back then. 

I did an interesting (to me anyway) experiment recently. I had my 
new switch and the old original rusty one which I had no idea if it 
had been tampered with in the past. Using some bits of hose and ac 
fittings, I hooked the new switch to my pressure regulator I use for 
HVLP paint spraying. Starting at 0 psi, I slowly increased the air 
pressure until switch closed. You can hear it close, and I used a 
meter to verify. I did this a few times and consistantly the switch 
closed at 40 psi of air. It was easy then to reset the original 
switch to match.   Might be useful if anyone has a bunch of switches 
with misadjusted settings lying around. At $9, just buying a new 
switch is probably the best idea.

Marty
#3765




--- In dmcnews@xxxxxxxxxxxxxxx, "Tom" <tomciodmc@xxxx> wrote:
> From: "David Teitelbaum"
> <SNIP>You could also have a low presure
> switch way out of adjustment. The compressor MUST cycle. Try 
adjusting
> it. It is the screw in between <SNIP>
> 
> NO NO NO, Do not touch the switch!! C'mon David... If the pressure 
is too 
> high on the low side then the switch will not activate. The switch 
doesn't 
> control the pressure, it's the other way around. The switch should 
disengage 
> the compressor when the low side pressure drops to between 29 and 
35. When 
> the pressure stays above 50 the switch will have nothing to do 
with it.
> Dirty or plugged condenser (the thing in front of the radiator) 
will cause 
> the high side pressure to rise. Plugged orifice will cause low 
side to be 
> too low and high side to be too high. Open (broken, missing) 
orifice will 
> cause the low side to read high and high side to read low.
> In this case the high side is a bit high, but without knowing what 
the 
> outside temperature was it's difficult to say... it might be ok. 
The low 
> side is way to high. This to me would indicate a problem with the 
compressor 
> or overcharged system. When there is too much refrigerant in the 
system 
> there is just no place for the compressed freon to go. It is 
forced through 
> the orifice at high pressure and keeps the low side pressure too 
high 
> causing the evaporator to freeze over. 36 ounces of R-12 is 
correct but that 
> applies to factory system in a D. That means that if you have 
shorter hoses, 
> smaller accumulator, bent/damaged condenser, too much oil, etc. 
then it 
> would be too much for the system.
> I would recommend charging the system with less freon. BTW, make 
sure that 
> you are really putting 36 ounces in there. Is your measuring 
system correct? 
> If you are using a scale, is it good? And the main thing is - Are 
you 
> putting 36 ounces by weight or 36 fluid ounces?? It's suppose to 
be a weight 
> measure. Or just switch to the metric system and use 1000 grams of 
R-12 :)
> 
> Good luck!
> 
> Tom Niemczewski
> tomciodmc@xxxx pl -> www.deloreana.com
> VIN 6149 (in Poland!)
> Save the dream so you can live the dream...







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