I'm having some air conditioning problems on my 1998 3.8L Mustang. When
the car is moving, the A/C blows cold air, but at low speeds (and even
worse when the car isn't moving), the A/C doesn't cool down the air at
I checked the A/C pressure with a gauge while the A/C was on (and set
to max). When the compressor is on, the gauge pressure is between 45
and 65 psi (this area is labeled "Alert"). When the compressor turns
off, the needle moves to the area labeled "Danger". This corresponds to
65 psi or more.
Do you know what the issue might be?
Any feedback is greatly appreciated.
The answer's the same as I posted on the mustang group.
Sorry if you dont like it.. but kudo's for figuring out where it should
have been posted, in the first place.
I assume the rad fan is running and the condenser coil is clean. If not,
fix that first.
See if you can find a hobbyist with a set of full gauges to help you.
There being something wrong, the gauge you are using is only an indicator
not a tool.
The reading you are getting with compressor on indicates either a bad
compressor or a damaged orifice tube (the little 'jet' that restricts
flow so as to produce cooling)
IOW, that pressure is too high, indicating either not enough flow through
the compressor.. or too much through the orifice. A hint as to which
would be the temperature of the vapor line at the compressor. If it's
near ice cold, likely the orifice. Likewise the line OUT of the
compressor to condenser being less than 'too hot to touch' would point to
bad compressor valves.
That last being too hot to touch, along with the pressure you're reading
would possibly indicate someone just 'dumped a can in' to see if it would
fix the problem.
The pressure you're seeing with compressor off means nothing, as
equalized pressure (no flow) relates to ambient temperature and is likely
twice '65' (look up a temp chart for 134a). This is ALSO why you cant
tell if there's too much or too little refrigerant just by reading some
pressure without the system running.
Summary: The gauge you're using assumes fully operational system with
the only variables being the switch-point of the low-pressure cutout and
the amount of refrigerant in system
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
yep, Most likely no fan. I have found all the dirt ends up in the
radiator, not the condenser. I guess it goes through the condensers
larger "holes" and gets stuck in the radiator. A garden hose does the
trick nicely. I have seen Crown Vics with radiators so plugged up you
would think they would overheat in a minute, but they just run a little
hotter than normal. Man I love a clean condenser and radiator! :)
Hi Backyard Mechanic et al and thanks for your feedback. My A/C
problems were indeed caused by a bad radiatior fan, just as you
indicated. I just had the fan replaced for $319 (parts + labor).
The A/C is now blowing cold air again. However, the fan is noisier than
the previous one --when it was working. It emits a humming sound when
it's on, so I'm going to have my mechanic take a look at it. Do you
know if the hum is normal? Will it go away over a few days?
As you can see I'm no car expert (although I'm very willing to learn)
so any input is very much appreciated here.
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