My 2001 PT has just started a strange thing a week or so ago. When I
start the car and it is at idle and turn on the A/C the system seems
to cycle the compressor on for a few seconds. No more than ten. Then
it is off for about 30 seconds and cycles on for several seconds and
then off again.
The air is obviously not cool. Now, when I start to drive off the
system works perfectly. Not only that, but it will cycle and cool
correctly while at idle and also work perfectly if turned off for an
hour or two and when started and at idle it will cycle and cool
This is a problem because when I transport my mother who is partially
paralyzed from a stroke, I need to set her in the car and then either
place her regular wheelchair in the back or if she uses her power
chair I have to pull the ramp out and load the chair in the back and
restow the ramp. Living in Florida necessitates having the A/C
running for her while waiting.
Stepping on the accelerator and racing the engine has no effect. The
Freon level is fine and the wiring is fine. There are no fault codes
and I and the repair shop are at a loss. I can't leave the vehicle
there overnight so they can see the problem. I am disabled myself and
with the dealership so far away, I can't ride with just the windows
open in 97 degree weather with sporadic rainfall and high humidity.
Sorry for the long story, but I wanted to explain reasons for not
letting the situation start where the repair shop or dealer can see it
for themselves. The car is a limited edition with 43000 miles on it.
I know we don't drive many miles. This problem seems to occur after
sitting overnight. Last week it was driven three days in a row and
each morning it was the same problem.
Of all the things I've lost I miss my mind the most.
You need to see what the pressures are when the a/c is on. The first thing
to check is the A/C fan assembly. When the A/C turns on the outside
radiator fan has to turn on, if it doesnt the system will go into a high
pressure on the high side and cut the compressor off. This will cause your
lack of cooling at idle. Driving down the road the A/C should work ok due
to forced air across the condensor by driving. You may also be
experiencing a higher then normal engine temp at idle.
Glenn - I have a question... First, thanks for your response. I am
running into a similar problem with my PT Cruiser. If you turn on
the air conditioner - what triggers the radiator fan to turn on?
Should the radiator fan be running whenever the AC switch is
Here is the path I've been down. Might be conspiracy theory - but -
maybe you can tell me if I'm nuts...
We initially fixed a pressure problem on the low side by replacing the
receiver-drier assembly. Recharged the system to find out the high
side pressure was off the scale. Radiator fan wasn't turning when the
AC switch was turned on. The non-dealership tech tracked down a
wiring diagram for the fan/PCM assembly, checked both relays, and
found that the PCM wasn't supplying a ground to the fan when AC is
switched on. He could artificially ground the fan -- and the AC
would work. This led to non-dealership tech telling me that PCM
needed to be replaced.... Initial thought was that he was nuts and I
went to a dealership to get it checked.
Dealership came back and definitively told me it was the radiator fan
-- even though the fan was operational on engine temperature control
relay. Replaced the fan -- AC worked for a about 2 days, cool
weather. I'm now back in the same situation. Went out to check the
car before returning to the dealership to find the fan not spinning.
If I turn on the AC, the fan does not engage. Service Rep is telling
me this is due to the lack of freon in the system -- which they
believe is due to a bad high pressure vent on the compressor. The
PCM is still able to engage the fan for engine cooling, and I'm not
seeing any temperature/overheat issues.
Question is... Am I a victim of Chicken / Egg theory? or is the fan
not getting a signal to turn on from the PCM and causing the freon to
The fan dual speed electric fan. It will always turn on when the a/c is on
unless the system is out of R134. The pressures will go extremely high if
the fan does not turn on and possibly blow the R134 out of the system
causing a low charge. The first thing to do is check for proper charge. This
may require a recover/weight and recharge procedure Your PT has 2 a/c ports
at the top near the passenger side and one at the bottom near the a/c
compressor. DO NOT USE THE HIGH SIDE PORT AT THE TOP< USE THE HIGH SIDE PORT
AT THE COMPRESSOR. If you use the high side port at the top it will not give
you an actual reading and will cause a problem due to false high side
readings. (High side pressure will show low at all times on this port). The
radiator fan operation is control by the Powertrain Control Module with
inputs from the temperature of the coolant, which is sensed by the coolant
temperature sensor, and vehicle speed which is measured by the vehicle speed
sensor. The PCM turns on the fan through either the high or low speed fan
relay. The PCM provides a ground to the relay's control circuit. The PCM
grounds the fan motor to engage it. If the motor is open circuit it will not
On Mon, 11 Jun 2007 05:36:11 -0400, "damnnickname"
Pressures are normal. Fan runs when A/C is turned on. Fan runs in
low and high speeds as needed. Forgot to state those facts. As when
I stated before (including this new information) all things except the
cycling run fine. Car never overheats. That surprises me since there
is no room in the engine bay for a cockroach to pass through sideways
with it's stomach sucked in! LOL.
The only work done on this car besides the normal maintenance, recalls
and regular manual listed mileage service is there was a leak in the
tranny vacuum modulator assembly at the tranny. Had that replaced,
new trans filter/fluid/flush/gasket et al. Found thermostat was stuck
open and replaced it. A small leak in the radiator and had that
replaced. Thank God for aftermarket extended warrenties !!!
My regular TRUSTED repair center and the dealership have no clue. They
cannot repeat the problem and find no fault codes. They state the
pressures are fine.
OK one more time, Are you having the A/C pressure checked at both ports near
the passenger side strut tower? If so you are NOT reading the high side
pressure. It has to be checked down at the A/C compressor discharge port or
the reading will be false. If you are experiencing a high pressure the
compressor will cut on and off and not cool at all. IF the system is working
when the tests are being performed it would be hard to say what the problem
is. Have you taken the vehicle in when the problem is happening?
I, myself, am not checking the pressures on the A/C. I am assuming
that either the Chrysler dealer or the <mechanic shop I take it to for
repairs has one person who knows where to check the pressures. But I
will take it back and mention this information. After all, to assume
makes an ass out of U and ME. LOL
Taking the car in results in the problem not occurring. Once the
vehicle is driven the compressor cycles correctly. It is just after
sitting for at the very least, overnight and starting it the following
day where it will not cycle correctly when initially started and not
driven off. The cycling is a short on period and the air coming out
is cool, just that with the short on and longer off cycle the air
isn't cool enough. Once, the car is driven any distance, even a
block, at even a slow speed, the compressor cycle is normal and will
remain so until the vehicle sits overnight.
I can leave the car idling after it is driven and the A/C will be cold
and the car not overheat in this hot humid weather. And leave it idle
for 15-20 minutes with only a slight reduction in the output
temperature which I attribute to idling and the compressor not
spinning fast enough. But it is still cold.
Not making an ass out of me!! LOL
Once again, it is a dual speed motor and when the A/C is turned on the
radiator fan must turn on also or it will develope problems. It does not
turn on from a high pressure switch. It turns on when the request for the
compressor is seen.
If I may add to the previous AC questions asked above; I also have a
2001 PT Cruiser that had air conditioning last year, but didn't work
starting this summer. I have taken it to my mechanic and had the
compressor replaced (because everything else checked out ok) and still
the compressor will not engage. I am told that the R134 is at the
proper pressure and that the compressor can be jumped. Even when the
compressor is jumped, there is not any cold air, because the fan does
not come on.
The fan does come on when the radiator temperature tells it to cool,
but from what I have read above, this should come on when I turn on
the air conditioner.
My mechanic says that there is an electrical problem, but has not
gotten around to tracing it. The temperature is starting to get real
hot, and I would love to have my air back. Is there anything I can
tell my mechanic to try before cutting open the wire harness?
Thanks in advance,
It sounds to me like the technician isn't familiar with the vehicle. The Fan
MUST come on when the A/C is requested. If the technician that is working on
the vehicle is using the A/C ports at the passenger side shock tower he is
not getting the proper reading. The high side MUST be checked at the high
side fitting down by the A/C compressor to get the correct reading. I would
be willing to bet that the compressor is kicking out because the high side
cut out switch is turning the compressor off and the reason it is going high
is because the fan assembly is bad.\
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