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Jim Grant's Tech Tips
‘89
Ford Aerostar, A/C Problems
Q: I have an ‘89 Ford Aerostar and the air conditioner takes
a break when it's hot enough to really need it. When the temperature’s
at or below 80, it's ice cold; much above 80 and everything seems to work
except the compressor. By turning it 'OFF' and then back 'ON' (sometimes
6 or more times) it will kick in and cool for a short period. It's been
"looked at" several times and it seems fine. There are no freon leaks,
gas pressure is normal. I have had "wide open throttle " switch replaced
twice, it made no difference. Where's the thermostat ? HELP! I'm going
to be in Florida this summer! This isn't the model year with the catch-fire
wiring, is it ? ....... Jean
A:You
want to ask the person who diagnoses your problem to perform a voltage
drop test from the battery to the A/C compressor’s electric clutch assembly.
Watch their eyes closely when you say this. Why? Either they are going
to look bumfumbled because they don’t know what you’re talking about (which
means get out of that shop), or there will be a look of understanding
mixed with curiosity, wondering how you would know about that test procedure.
One of the problems we’ve seen with A/C systems such as yours has been
a loss of battery voltage available to the A/C compressor clutch. The
condition is not a complete loss, it’s just a drop in voltage available
which is just enough to cause problems. This doesn’t present a problem
until the temperatures climbs. As the A/C system works harder (high air
temperature) the demand for electricity increases. An electrical circuit
just by its nature will make its own heat. This internal heat interferes,
actually creating more internal resistance, reducing the flow of electricity
even more. The end result is an A/C system that will stop working when
you really need it. The fix is identifying the switch or contact that
is resisting the flow of electricity or installation of a relay kit to
provide power to the A/C compressor.
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