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Car Overheats slightly and car shakes when A/C is on??

 
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Old 04 Jun 2012, 07:48 pm
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Question Car Overheats slightly and car shakes when A/C is on??

Hey Fellow Pt Owners,

I own a 2002 Non-Turbo Pt Cruiser with 150,000 miles and live in San Antonio, TX. Weather here has just reached the high 90's within the past 2 to 3 weeks or so.

Well I've certainly had some fun times with my car, but trying to narrow down the possibilities on my latest problem. About 1 1/2 years ago i had my car engine and radiator replaced: Process summed up was cracked radiator, lead to overheating, tried to replace radiator myself and did it incorrectly, waters spout/stems on bottom of radiator snapped off on highway, lead to cracked header. Now new radiator, thermostat, hoses, water pump, coolant, timing belt, and battery. Car has been running great ever since, until two months ago, the car was shaking during idle (narrowed it down to when the A/C was on). Made sure engine mounts were still good, because i've had that problem in the past an i wanted to make sure that wasn't an issue. Couldn't figure out why so i thought it was related to the A/C at first, then about 3 to 4 weeks ago i noticed that it started to overheat slightly only on idle when i had the A/C on, but would go back to normal when i turned it off. As the temperature has been getting hotter it is beginning to overheat easier, unless i am on the highway. It will not overheat though when the A/C is off. Checked the fan and it is moving, speeds up more when it warms up and A/C is on. I noticed though occassionally the A/C would stutter at first to kick on the compressor for a few minutes. In other words just blowing warm air and i could feel the car move a bit, like the compressor was trying to kick on, then the cool air would start flowing.

Now my theory: The crack during my first heating problem could have been caused by the same problem i am currently having. In other words the fan is moving, but not fast enough when the A/C is on. Some people have told me a fuse, relay, or control module (hi or Low on the fuses & relays). So i'm thinking it has to be something around this area.

Question: Am i missing something, can someone explain the operation of this part of the fan cooling system? (Switching from low to high speed and how it relates to the A/C compressor) Any help is greatly appreciated, since this can be a real pain in Texas heat and i don't want a cracked or warp head again for a simple fix.
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Old 04 Jun 2012, 08:03 pm
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Location: Detroit, MI
Posts: 103
Default Re: Car Overheats slightly and car shakes when A/C is on??

The fan has 2 speeds, one that comes on when the A/C is turned on, and one that comes on when the temp gauge reaches half way.

When the car is cool, start it up and turn on the A/C. If the fan doesn't immediately kick on, one of the speeds has gone bad, which is quite common. The fan could still come on later when the engine warms up, but the fan not running when the A/C gets turned on will cause the engine to shake at idle and the air to blow warm.

Based on your cars mileage, you fan is well overdue to fail, if it hasn't been replaced already.
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Old 04 Jun 2012, 08:18 pm
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Default Re: Car Overheats slightly and car shakes when A/C is on??

The fan was replaced, i'd say maybe 2 to 3 years ago. A newer model from the chrysler dealership parts store. I knew about the two speeds, i just always though it was a low speed when you turn on the car (whether a/c was on or not), then a high speed when it reached the halfway point, which it reached that point faster with the A/C turned on.

So is the correction, then fan should be off when it is cold and the car is on with no a/c and below halfway point Temp. Then on low speed when the A/C is on regardless of whether it is warm or cold, and high speed when it reaches the halfways point regardless of whether the A/C is on or not. As always any additional information is appreciated.

Thanks,

Anthony
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Old 04 Jun 2012, 08:38 pm
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Question Re: Car Overheats slightly and car shakes when A/C is on??

Ok, I went outside to check the fan. Car was still warm, but below half on the temp gauge. Turned the car on w/o A/C and the fan was not on at all, touched and moved it with my fingers. Went to the car and turned on the A/C, fan was on and the car was still below the halfway mark. Put the A/C on full blast to warm it up. Temp climbed to normal while i was in the front of it, with one hand by the fan and another in front of the radiator to see if there was a change. Also checked upper hose for heat and firmness so i could know when it reached the midway point. Temp climbed to normal and stayed there, upper radiator hose was firm and red Hott, but i could not see a significant change in fan speed or air pull from the radiator side. Not sure what to make of it, car was rough (noticable change, not severe) as soon as A/C was on. Any suggestions?
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Old 04 Jun 2012, 10:06 pm
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Location: San Antonio, Texas
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Default Re: Car Overheats slightly and car shakes when A/C is on??

Sounds like the head pressure on the compressor is getting to high. That's probably what is causing the stumbling or rough idle. Most likely cause is the radiator fan not blowing correctly. I have seen them work on the low speed but not the high. It can be hard to pinpoint because the a/c will work sometimes at idle and then sometimes it won't. You said you had the fan motor replaced 2-3 years ago. It's probably time for another one. As much as I hate to speak ill of Mother Mopar the fans on the PT's are crap. If you want me to take a look at it then drop me a line at slartyblarfast@aol.com subject PT fan. I'm no longer working on Mopars but still have my 06 gt and stilkl love'em!
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Old 05 Jun 2012, 10:05 am
quicksilverdon's Avatar
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Default Re: Car Overheats slightly and car shakes when A/C is on??

Sounds as if high speed on fan is gone - when High comes on with hood open, you notice it - the noise level goes up a LOT.
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Old 05 Jun 2012, 08:32 pm
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Default Re: Car Overheats slightly and car shakes when A/C is on??

It's the fan. Classic symptoms. Sometimes our fans "sorta" work--but not enough to cool the "high side" pressure, via the A/C condenser. The high-side pressure builds up, putting a lot of excessive load on your engine (at idle when the A/C is on)--and it sputters and shakes.

Test the fan--both speeds--using the battery-jumper-cable trick.

When my fan was going out, I could actually turn the fan blades a bit with a screwdriver and the fan started spinning ... but then it stopped a short while later. My new fan is OEM (dealer installed), but when (not if) my engine starts that same crap at idle with the A/C on, then I'm just going to put in another fan. But I've gotten 30,000 miles from the replacement fan with no problems thus far.

Tim
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Old 09 Jun 2012, 01:28 am
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Default Re: Car Overheats slightly and car shakes when A/C is on??

Well i replaced the fan yesterday, and ran it for about a half hour with the A/C full blast after it was already warmed up. So far it hasn't even hit the midway point, stayed underneath it pretty consistently. I'll let you know in a few more days if everything stays the same. Now i have to check my timing belt area, pretty sure i have a oil leak from the camshaft seals or crankshaft seals.
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Old 09 Jun 2012, 10:06 am
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Default Re: Car Overheats slightly and car shakes when A/C is on??

it's amazing how many PT owners problems are solved by changing the rad fan...
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Old 09 Jun 2012, 05:13 pm
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Default Re: Car Overheats slightly and car shakes when A/C is on??

Harry, just keepin it cool ....

Tim
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a/c, air condition, fan control module, fan relay, overheating


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