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AC blow hot at Idle, cold when moving

Old 07-20-2016, 03:26 PM
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Default AC blow hot at Idle, cold when moving


*Need some help? I have a 03 Saturn Vue 2.2L. I have only one fan for both the radiator and condenser. First, (after talking to a GM guy) should the Fan turn on as soon as I turn on the A/C switch? The problem I have is that at an Idle the car blows hot air. The compressor is on and reading good pressure, the fuses and relays are all good , replaced the whole fan assembly with a new one and the wiring to the fan is good. However when I turn on the A/C the fan does not turn on. When the car reaches about 230 the fan kicks on and cools down the car to normal operating temp. So the fan works for the engine Temp sensors. While driving down the road the A/C blows Ice cold (my though is because now it has air flow over the condenser) however when I am stopped the air goes back to hot. Ideas???
Old 07-20-2016, 09:08 PM
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I have replaced all fuses and relays concerning the A/C system minus the ac diode
Old 07-20-2016, 09:37 PM
derf's Avatar
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This is a guess based on my limited knowledge of ECU functionality.
I do not claim to be an expert nor do I claim the following to be correct.

But it is my guess, given that the components of the system all seem to function, just not necessarily at the correct time.

The A/C relay is good as it receives the ECU's signal (is energized by supplied Voltage) to engage the AC compressor clutch.

The fan relay is good as it receives the ECU's signal (is energized by supplied voltage) to engage the fan based on the ECTS reading.

What appears not to be good is the ECU's signal to the FAN Relay when the AC is engaged.

I believe there should be an AC request and a FAN request sent to the ECU on separate pins. It may be that the FAN request that SHOULD be generated by the AC head unit is either no longer being generated OR there is a wiring problem between the AC head unit and the ECU FAN request pins. Or just a bad ECU.
Old 07-21-2016, 09:46 AM
02 LW300's Avatar
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You need to get the car on a scanner with data and see if the a/c request is present or not. Diagnose from there. I have been working on Fords for the last 12 years and their pinpoint tests are very good. I am sure the Saturn factory diagnostic manuals have a similar set of step by step instructions.
Old 07-25-2016, 07:15 PM
Join Date: Jun 2016
Posts: 44

I would also check to see that your a/c is properly charged. I have a Mitsubishi that acted similar, turns out it just wasn't fully charged. Bought a kit from walmart and charged it up and it worked just fine after that.
Old 08-02-2016, 05:54 PM
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Join Date: Jun 2013
Location: Central Kentucky
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If the compressor is short cycling at idle, that could be an indication of low charge. If it is short cycling, take it to someone who has a set of gauges for HVAC and see what the pressures are. The suction and discharge pressures will tell if it is low or not.
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