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Old 04-14-2012, 11:28 AM   #1
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Default Radiator Fan question

Again, sorry of this is in the wrong base, I don't seem to have access to post new threats in the tech bases. (Ya, I'm the new guy--forgive me!)

Simple question, on a Chevy Venture Van 2001, even when its "cold" should the radiator fan'* spin in low mode when you turn on the AC?

I'm having some intermittent issues with my AC not working---but when it dose work, it works great. When it fails, I can still see the compressor clutch engaged, and but the radiator fans sometimes don't spin. I have swapped relays, and willgled wires, and that sort of thing, but I cant seem to pinpoint the cause of the trouble.
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Old 04-14-2012, 12:48 PM   #2
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No trouble at all. Your HVAC system controls the fans depending on engine temp and A/C request.

When the A/C is turned on, the fans may or may not turn on based on the sensor readings inline with your A/C hoses. It'* all based on the pressure of the system. Sometimes they turn on low, sometimes they goto high speed. What you are seeing is perfectly normal.
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Old 04-14-2012, 02:27 PM   #3
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yeah, completely normal.

the fans kick on and off for A/C usage based on the high-side pressure. goes above a certain pressure, fan(*) come on, if it keeps rising, the PCM will either disable the compressor or turn on another fan/switch to a higher speed(depending on how high it gets).

sounds like you have intermittent low pressure if the fans sometimes don't come on and cooling ability is bad.
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Old 04-19-2012, 07:38 PM   #4
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Here is what I have observed...

Cold start (motor is cold)....

AC engage.
System blows nice cold air right from the get go.
Seems to work just fine till about the time I hit my first stop on the drive home from work. (less then 2 blocks). At that stop light, the air temp seems to rise sharply, and I can feel the humidity of the cabin rise sharply too. I'm not 100% sure, but I think the compressor is still engaged even tho the AC starts to suck at this point.

Driving for the next mile or, while the motor temp is reaching normal...the ac seems to cut in and out. Appears to work better in motion then at stops, not its almost like its kicking on and off at random.


Then once motor temp is normal, the AC starts to work consistent for the rest of the 8 mile drive home, no problems at all, icy cold.

As a troubshooting measure, I removed 1 radiator fan rely, and shorted it to make 1 fan run at full speed all the time. Service Engine light came on when I did this---but the AC seems to work perfect from cold to hot, to end of trip.

I figured maybe that relay was bad, so I swapped them all around (with other exact relays), but I still have this problem.

Service engine light is off when all realys are installed and shorts removed.

Maybe a bad pressure sensor?
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Old 04-19-2012, 07:41 PM   #5
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Also, I never get over-temp, stays well within range and out of the red.
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Old 04-19-2012, 09:46 PM   #6
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When stopped and A/C running, the compressor isn't moving much refrigerant throught the system. Same with the air moving through the radiator. It'* normal for the engine temp to increase and the temp of the air coming out be a tad warmer. Once the car is moving, the RPM'* are higher, thus making the A/C compressor move refrigerant more which equals colder A/C and a cooler engine. When the HVAC is commanding A/C, the PCM controls the fans based on engine temperature and the pressure of the A/C system.
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Old 04-19-2012, 09:55 PM   #7
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Ya, my vent temp goes from 40 to about 90 during that first couple of stops, but then after the motor is warm, it goes from 45 to may 49 during stops.

I think there are various fan speeds....off, low, medium, high? I think Im missing low???
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Old 04-20-2012, 06:19 AM   #8
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Are you talking about the blower motor fan speeds? You should have off, low, med, high. If I remember my 95 B-ville, low was so slow, you didn't even feel it coming out. But it did work.
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Old 04-20-2012, 03:19 PM   #9
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No, radiator fan speeds is what I'm referring too. I think the computer is calling for them, and most of them work, but maybe one speed request (low, or medium) is resulting in no radiator fan at all. Pretty sure when that happens, the AC system dosent 'stop working' its just that without a radiator fan spining, there is no exit for the heat.

Is there a "cheep way" to hook up a 'code sender' to this van? I know with that you can tell the computer to engage the radiator fans for troubeshooting. A code reader is not good enough. And trying to do it live is just too hard while driving, pulling over, getting out, looking, and by then the temp/pressure has changed and engages some other speed of the fan.
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Old 04-20-2012, 08:26 PM   #10
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I don't know of any code readers that has bi-directional control other than HPTuners, EFILive, and some high end Snap-On/Tech2 diagnostic equipment. Which run a couple grand.
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