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Rough idle when AC is on

 
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  #1 (permalink)  
Old 01 May 2015, 12:46 pm
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Default Rough idle when AC is on

Edit: 2006 Pt Cruiser 140k miles

So I have this problem where if the AC is on when idling (sitting at a light for example) the engine bogs down a lot. It has stalled out once, but with it getting hotter I'm sure it will get worse.

I took it to a shop I trust and they said the AC was getting to over 450 psi (or whatever) and the engine would start to bog down. The cooling fan needed replaced. I'm paraphrasing here of course, so not sure if that makes sense.

I started to do my own experiments and sure enough if the AC is on at idle the fan will NOT turn on until it gets just over the half way mark on the temperature gauge. When the fan turns out it blow out cold air and the idling turns back to normal. A minute later the fan will cut off and back to getting bogged down after 15 seconds and just keeping at it every 15 seconds or so. Two minutes later when the temp gauge gets back to just over half the fan will turn back on and it repeats this process indefinitely.

The fans don't cost too much ($100 or there abouts), I just want to make sure this is the cause. I mean the fan is working. It turns on. At "low" or "high" speed I have no idea.

It just seems like the fan works but only when it hits half way mark on the temp gauge. Then cools the engine then goes back off then the AC starts to bog down the engine. So is it the fan? It seems to be working correctly, but it would make sense if it worked all the time not just at the half way point on the gauge and everything would be perfect.
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Old 01 May 2015, 12:51 pm
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Default Re: Rough idle when AC is on

Check that the fan is running when the AC is on. If not that's your problem. Also air idle control valve.
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Old 01 May 2015, 01:03 pm
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Default Re: Rough idle when AC is on

Quote:
Originally Posted by Busted_PT View Post
Check that the fan is running when the AC is on. If not that's your problem. Also air idle control valve.

It only runs when the temp gauge needle goes a bit above half way point. Then for a minute it runs fine then it (the fan) turns off then bogs down excessively.
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Old 01 May 2015, 01:56 pm
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Default Re: Rough idle when AC is on

Quote:
Originally Posted by packer43064 View Post
It only runs when the temp gauge needle goes a bit above half way point. Then for a minute it runs fine then it (the fan) turns off then bogs down excessively.
When the ac is on it should run all the time. There are two sides to the fan. Low and high. Your high is working. But to be sure it's the fan you can run a jumper to both sides of the fan to see if one still not working. That will rule out othe possible causes. The ground pin is the middle one. If one side doesn't run. Buy you a fan. I wouldn't run the ac until you get this fixed.
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Old 01 May 2015, 08:22 pm
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Default Re: Rough idle when AC is on

Quote:
Originally Posted by Busted_PT View Post
When the ac is on it should run all the time. There are two sides to the fan. Low and high. Your high is working. But to be sure it's the fan you can run a jumper to both sides of the fan to see if one still not working. That will rule out othe possible causes. The ground pin is the middle one. If one side doesn't run. Buy you a fan. I wouldn't run the ac until you get this fixed.
Thank you. Would some alligator clips clipped to the battery work or would I need some kind of multimeter? Does the car have to be on if I use the actual battery to test the fan?
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Old 01 May 2015, 09:36 pm
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Default Re: Rough idle when AC is on

I would suggest getting a new radiator fan. The radiator fan are one of the most common parts on the PT Cruiser that needs replacing. On my PT Cruisers I replaced the first one at 70,000 miles. With your PT Cruiser at 140,000 miles its a good chance you are due for the third new radiator fan. Its a peace of mind having a new radiator fan in your PT Cruiser only costing $84.00 knowing that you have a better chance of not overheating the engine. I even have a brand new one in the garage in case one of my radiator fans start to give me a hint of going out.
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Old 03 May 2015, 03:49 pm
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Default Re: Rough idle when AC is on

Thanks for the help guys. I just bought a new fan for $95 with shipping. Affordable IMO.
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Old 03 May 2015, 05:03 pm
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Default Re: Rough idle when AC is on

Quote:
Originally Posted by packer43064 View Post
It only runs when the temp gauge needle goes a bit above half way point. Then for a minute it runs fine then it (the fan) turns off then bogs down excessively.
As Danny stated... Fan should run all the time when wheels are not turning. Check your speed sensor.
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Old 03 May 2015, 08:48 pm
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Default Re: Rough idle when AC is on

Radiator fan operation is controlled by the Powertrain Control Module (PCM) 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.

P0480 - Low Speed Fan Relay Control Circuit

Ground Circuit
Low Speed Rad Fan Control Circuit Shorted To Battery Voltage
Low Speed Rad Fan Control Circuit Open
Low Rad Fan Control Circuit Shorted To Ground
Radiator Cooling Fan Module
Totally Integrated Power Module


P0481 - High Speed Fan Relay Control Circuit - An open or shorted condition detected in the high speed radiator fan relay control circuit.

Possible causes on the 2006 model year and later include:

Fused (B+) Circuits
Ground Circuit
High Speed Rad Fan Control Circuit Shorted To Battery Voltage
High Speed Rad Fan Control Circuit Open
High Speed Rad Fan Control Circuit Shorted To Ground
Radiator Cooling Fan Module
Totally Integrated Power Module

Last edited by ptcruisersteve; 03 May 2015 at 09:14 pm.
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Old 03 May 2015, 08:53 pm
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Default Re: Rough idle when AC is on

Quote:
Originally Posted by 767skyking View Post
As Danny stated... Fan should run all the time when wheels are not turning. Check your speed sensor.
767skyking,
Excellent point. If the speed sensor was bad wouldn't it also be effecting the
speedometer and transmission?
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