You know it's fully charged how? The low pressure switch (LPS) cuts off the
compressor clutch power at 22~25 psi and won't allow power again until the
pressure builds back up to about 45 psi. Constant cycling at short (10 second)
intervals usually indicates low refrigerant, where 20 sec~30 sec intervals are
normal. Check the low side pressure and if it's within the above ranges, the LPS
is suspect. Test the LPs by jumping the LPs connector with a piece of wire.
How do you know the system is fully charged? It sounds a little low. R-134a
on newer vehicles have a smaller capacity and just a few ounces will cause this
symptom. The charge amount is pretty critical. A couple of things to check,
Is the interior fan working properly on all speeds? Is there good airflow out
the vents? Is the blend door (hot-cold control) working and adjusted properly? A
and dirty check is to see if the accumulator is cold and sweating (condensation)
the engine at high idle. If so, it should be cooling pretty well.
To check the refrigerant system correctly you need to know both the high and
side pressures along with the ambient temperature. Also need to know if the lack
cooling happens at idle\low speed, cruising speed or all the time. The low side
from the parts store really don't tell you anything useful, if that's what you
Another often overlooked part is the engine cooling fan clutch. A weak clutch
cause poor cooling at idle and low speed and ocassionally compressor cycling due
high head pressure. At 1500 RPM the fan should pull a LOT of air through the
Check the easy things before you start chasing electrical bugaboos that
arent there. There is no WOT switch, just a high pressure cutout and a low side
cycling switch. They do fail but not very often.
Thanks for the responses everyone. The pressure was checked with one of
those red/green/orange gages from advance auto, the kind attatched to the
can, it read green so I did not charge it. great airflow from the vents,
cold too, for a few seconds. Blend, hot cold working well too. Also sweat
from the accumulator. it seemed to start out as a problem just at cruising,
idle would run comp. always, but now its also cycling at idle too. Fan
clutch is drawing ALOT of air.
I just replaced the original battery with oem battery (9.5 yrs on it). But
this problem was in the works before I replaced it.
Thanks for any help.......... T.J.
how do you know it's at full charge?
how do you know it's not leaking? Did you test it with a sniffer? or
just look for oil traces... not a sure indicator!
You say it cycles every ten seconds... do you mean it's off ten and on
one second or less?
If so... almost surely low on refrig.
But you didnt mention the low side gauge reading during this cycling...
which brings us back to "how do you know..."
There is no WOT switch, that comes from the PCM logic, reference the TPS
and maybe the MAF. If the cycling is at a steady rate, that's ruled out.
To illuminate the other two answers...
It only takes a couple tablespoons of refrigerant to have the pressures
seem normal in the static (not running) state. That's how A/C works!
I disagree with the need for a full set of gauges to remedy the possible
problem... but ONLY if you understand the physics on how your A/C works.
Which, if you are going by the static pressure, you dont.
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