Re: More a/c questions

["Harold McElraft" <hmcelraft@xxxx>]

I don't usually get into the correction business but there is a 
reason the AC compressor is called a compressor.

The theory of refrigeration requires a "compressor" otherwise there 
is no way to attain the liquid to gas process that removes heat from 
the air passing over the evaporator. The orifice tube regulates the 
liquid to gas process at the evaporator. A clogged system with a 
functioning compressor can blow the system apart; that is why there 
is a safety valve and/or a high pressure switch. Too much Freon will 
cause a too high pressure on both the high and low side in an 
unclogged system. The orifice tube creates the differential that 
causes cooling. At the ideal charge, the entire evaporator removes 
heat (feels cool). If the system is undercharged only a portion of 
the evaporator is removing heat and pressures are too low (the quick 
clutch cycling or no engagement of compressor). BTW, if the 
compressor ran with an undercharged system a vacuum can be created 
on the low side. If the system is over charged the pressures are too 
high and the evaporator does not remove heat because there is not 
enough expansion room for the Freon in the evaporator. There are 
other important functions that create the cooling; the fans remove 
heat in the liquid in the condenser (it became a liquid by 
compression), the amount of air crossing over the evaporator, etc., 
etc.

Further, getting the correct charge in a system is a bit of an art 
without the correct equipment. You need experience in reading the 
differentials on the gauges at different outside temperatures and a 
minimum of specialized equipment. Working on the AC system can be 
very dangerous especially if you are still using R-12. A little R-12 
in a running engine intake can create a killer gas. I suspect most 
owners are best off leaving this service to a specialist.

Harold McElraft - 3354




--- In dmcnews@xxxxxxxxxxxxxxx, "content22207" <brobertson@xxxx> 
wrote:
> Don't know R12 static pressure (R134 is 90 - 100 PSI), but tech 
manual
> N:05:01 STARTS at 60 PSI. Would imagine anything less trips low
> pressure switch as soon as cycle starts. Take it back at least to 
60
> PSI then begin diagnosis.
> 
> High and low side pressures are on page N:06:01 (or page N:09:01).
> Remember: A/C can appear backwards -- high side reading too LOW 
means
> system is clogged (most people think opposite simply because it's
> pumping there. Actually no way compressor alone could emulate 
physics
> of refrigeration. In fact, have been told heart of whole operation 
is
> suction, not output). You need a good cycle to get into 200 plus 
PSI
> range. When everything's clear you should see low side drop and 
high
> side climb (hence the names). 
> 
> BTW: This is one reason I do most of my work on low side. Reading 
too
> high -- system is clogged (hot air from vents) or overcharged (cold
> air from vents). Too low -- freon is low (assuming PSI drop has
> occurred). Makes more sense. Plus on a 134 conversion most people 
just
> put quick connect on low side only.
> 
> RE: compressor cycling -- under optimal conditions it is NOT 
supposed
> to cycle. Note on page N:01:01 that cycling is response to frozen
> evaporator (blocked by ice -- remember clogged high side LOWERS
> pressure). If system is clear, freon level correct, and DeLo 
sitting
> in the sun, compressor should run continuously. Cycling compressor
> means something's wrong.
> 
> BTW David T: thought some more about iced up evaporator on my Two 
Tone
> Lincoln last year. Ford's freon metering device ("throttle 
suctioning
> valve") has no compressor shut off feature. Does have an orifice
> bypass line, but that's usually triggered by a stuck expansion 
valve
> (WAY too much freon). My conversions are probably splitting the
> difference -- too much freon into evaporator due to higher R134
> pressures psyching out TSV, but not enough to open bypass circuit.
> Only getting away with it by passive heat radiating from heater 
core
> and continuously melting ice (is only separated by a plastic door).
> Remember: froze up when heater core was bypassed due to leak. 
Hasn't
> frozen since.
> 
> Same principle must apply to my DeLo. If it isn't passive heat from
> heater core (good reason to use "Norm" setting vs "Max"), may be
> because interior absorbs so much sun!
> 
> Bill Robertson
> #5939
> 
> >--- In dmcnews@xxxxxxxxxxxxxxx, "geek123y" <ken@xxxx> wrote:
> > List :Members
> > My car had loss of R12 the compressor stopped and wouldn't come 
on I 
> > added 1 pound of R12 and some die and ran it for a week it was a 
slow 
> > leak at the condesor fitting