[DML] Re: A/C Question

["Harold McElraft" <hmcelraft@xxxxxxx>]

First of all, working on the AC system can be dangerous. Based on 
what you have accomplished thus far you seem quite knowledgeable - 
but, I don't know your level of knowledge in refrigeration.

The pressures would appear to indicate a full system if the RPM is 
near 2000. At idle, those pressures indicate an undercharged system. 
But, we know the system is undercharged because you could not get 
all the charge into the system. Any pressure above 30 psi on the low 
side will keep the compressor on. High side should be closer to 200 -
 235 psi. So, I'm guessing you are low on charge and at idle.

If you have the RPM's at 2000 then you probably have air in the 
system but I am doubting this as the high side would be really high. 
If at idle, then going to 2000 RPM will probably cause the system to 
start cycling - too much - it will also allow you to put in the rest 
of the charge by adding refrigerant to the low side of the system as 
the pressure drops.

At 1,034 feet elevation in New Stanton you need closer to 29 inches 
of vacuum to boil all the moisture and air out of the system at 75 
degrees. One way to do that if you can only get 28 In.Hg. from your 
pump is up the temp in major components by using a hair-dryer or hot 
air gun. Are you using R12 or R134? I assume 134 based on the charge 
you mention. 36 oz is correct for 134 - 40 oz for R12 - although it 
depends on what bulletin you are reading. I prefer the 40oz level 
for R12. The R134 conversion rule is 90 percent of the R12 charge.

A full R12 system will cycle at 75 degrees (2000 RPM). Using 134 you 
should expect a little less cycling because the pressures are 
typically a bit higher. Heat the cans of refrigerant with a hair 
dryer to get all the gas in the system - don't invert them, let gas 
only into the system. Did you use the correct oil? Amount and type? -
 PAG (polyalkaline glycol) oil, specifically PAG/100 oil for the D 
compressor, is compatible with all common refrigerants including R-
12 and R-134a - however, the mineral oil in a stock D (mineral/500) 
is not recommended with 134. Flushing out the old oil is necessary 
when using 134.

Harold McElraft - 3354


--- In dmcnews@xxxxxxxxxxxxxxx, "Dave Stragand" <dave.stragand@xxxx> 
wrote:
> Hi All,
>  
> I hooked up the A/C on Project Vixen today, evacuated it, and 
charged it up.
>  
> I evac'ed the system for about 90 minutes, at 28" Hg, then charged 
it up.
> The low side pressure is at 32, the high side at about 170-175, 
and the temp
> today was about 75 F.
>  
> The system is blowing pretty cold (though not sure how cold, as I 
cannot
> find my A/C thermometer anywhere) but the compressor isn't 
cycling -- it
> just runs continuously.
>  
> Following the checklist in the workshop manual, it says to check 
for missing
> expansion tube (it's in there, and it's new), or that the system is
> overcharged.  Considering it only would take in about 28 ounces of 
R12, and
> the service bulletin calls for 36 oz, I don't think it's 
overcharged.
>  
> (I do have one known small leak, on the Schrader valve on the low 
side hose
> at the compressor.  I'm going to see if I can track down that 
nifty little
> tool that allows you to change it without evacuating the A/C.  For 
now, I
> have a plastic o-ringed sealing plug on it to help slow/stop the 
leak.)
>  
> I did have a problem where the back of the high-pressure cutoff 
switch came
> off while I was mounting the high side hose, but it snapped back 
on without
> a problem.  The compressor, accumulator, expansion tube and low-
pressure
> switch are all new.  Does anyone have any other suggestions as to 
why the
> compressor will not shut off?  
>  
> -Dave Stragand
> VIN #05927
> http://www.projectvixen.com
>  
> 
> 
> [Non-text portions of this message have been removed]




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