Over the weekend, I drove my MIL's PT Cruiser and noticed the engine was having issues with the A/C engaged.
When idling, every ~10-20 seconds the engine would shudder, the tachometer would jump around, and the car felt like it was going to stall. It never actually did stall out. The car never had a particularly smooth idle but it was never this bad. The problem seems to go away with the A/C turned off.
I've done the usual stuff -- new air filter, new plugs & wires, ran a bottle of Techron through the tank.
I wasn't sure what the next step should be.
Idling engine shudders when A/C on
- Thread starter kb01
- Start date
- Status
Try fuel filter, and IAC.
those cars have problems with the electric cooling fan.If the fan doesn't come on when the ac is turned on the ac aystem will build up too much pressure and cause the problem you descdribed.Go look to see if the fan is on when the ac is on.
Take a look at the throttle body, it may need some cleaning.
Originally Posted By: Chris142
those cars have problems with the electric cooling fan.If the fan doesn't come on when the ac is turned on the ac aystem will build up too much pressure and cause the problem you descdribed.Go look to see if the fan is on when the ac is on.
Could it possibly be an idle up valve? I know my car has one - it raises the RPMs a few hundred while idling when the A/C compressor is engaged.
Originally Posted By: KrisZ
Take a look at the throttle body, it may need some cleaning.
Wow, thank you for all of the advice!
So, a reasonable course of action would be to:
1) Start car, run AC and see if radiator fan is turning on. If not, replace the fan.
2) Clean the throttle body.
3) Replace Idle Air Control valve
4) Fuel filter.
According to all those links posted above, issues with the fan seem to be a major problem.
Really stupid design with the Cooling system on these cars. The low pressure cycling switch that cycles the compressor on and off also cycles the Radiator fan on and off at the same time.
This constant on and off burnes up the radiator fans lower speed. High speed still works if the engine gets hot enough.
You may have that wrong if my Chrysler product has the same strategy.
In my car the fans are on anytime the climate control is engaged. But the low speed is HALF voltage. That is not likely to do much at all to a motor rated for 12-14 volts!
Trust me, if the fan is bad at low speed it isn't going to run high speed. Maybe a relay dropped but the motor is either good or bad, period.
Originally Posted By: SteveSRT8
You may have that wrong if my Chrysler product has the same strategy.
In my car the fans are on anytime the climate control is engaged. But the low speed is HALF voltage. That is not likely to do much at all to a motor rated for 12-14 volts!
Trust me, if the fan is bad at low speed it isn't going to run high speed. Maybe a relay dropped but the motor is either good or bad, period.
Originally Posted By: Chris142
The Pt fan motor is actully 2 motors with 2 sets of windings......Trust me when I say that one speed can stop working and the other speed works fine.
I see 2-3 of those cars with the same problem every week.
Could be a TPS if it has one. Symptoms are up and down idle every few seconds. Replace it anyways, not expensive. A dirty IAC V symptom is idle too low when warm. When AC kicks in gets real low because of the compressor load and attempts to recover. Process repeats. Slower than the TPS symptom. An AC compressor that hasn't been charged in a long time could be low on, or have spent PAG oil = hard turning compressor, loads the engine down when the compressor clutch is engaged at idle.
Last edited:
Originally Posted By: kb01
[quote=Chris142]
Can you recommend an aftermarket replacement or do you stick with OEM?
A throttle body cleaning and idle air control motor cleaning are very good maintenance, and need to be right.
Most likely they will solve the problem, but if not, you did a very good thing .
The fan problem may be the key, but that is very vehicle specific.
don't forget relays and wiring faults.
I'd pull that fan motor and test it with some direct 12v
Odds are its indeed the fan- something of a weak spot on the PT. I disagree that the design of the way the fan works with the AC system is to blame, my daughter's 99 Jeep works that way and has its original fan at 140,000 miles. Also I think the PT actually changed the fan logic during the years it was produced- wifey's 2005 doesn't cycle the fan directly in sync with the AC clutch. Its under full computer control- the fan comes on briefly when you start the vehicle regardless of temp, then cycles occasionally as the engine comes up to temp (even with the AC off, presumably to move air through the engine compartment and also over the oil-to-air tranny cooler). With the AC on, it either stays off or runs at either high or low speed as dictated by the condensor high pressure switch.
yes, modern vehicles run the fans for a variety of reasons.
I was quite surprised that the same parameters trigger the PT fans as trigger my LX. On mine, the fans run at low all the time if climate control is on. I get a high speed burst when first started after a heat soak. Then I can get high speed for trans temp, AC high side pressure, or coolant temp.
- Status
Similar threads
