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2001 Chevy Venture Trying to kick my butt

GM Tech on Wed May 23, 2012 9:00 PM User is offline

Year: 2001
Make: Chevrolet
Model: venture single system
Engine Size: 3.4
Refrigerant Type: 134a

So here it comes- complaint is doesn't cool all the time-- charge level pulled and weigheded out fine...

Seems I get no a/c request at all- and when I check a/c rquest signal (grn/wht wire) from control head- I get no voltage-- Tech II will energize a/c relay and compressor- when reuested on Tech II relay checker...but this thing was cooling fine when I drove it into my shop...

Okay- plot thickens-- I thought since I was having no luck parked- and that owner says a/c is intermittent- and my test it has been several hours running with no a/c request at all-- that I should take it out and drive it---with volt meter attached to drk grn/wht at PCM--and tech II showing no a/c request- I drop it in reverse and a/c request is suddenly yes and volt meter show +5v---Then back in park and request is no and volt meter is zero....drop it in drive- request comes on , then drops out--RPM related? I can reve it any amount in park and a/c request and volt meter are negative....drop it in any gear, or neutral and request is now intermittent- but mostly on-- just as owner states....WTF I say....older vans 1996 or so had a lead from control head that fed TCClock-up- so that torque converter would lock up with a/c on-- to keep from feeling engine drag and cycling clutch I assume---but do these newer ones 2001+-- the schematic for HVAC shows none--

.I get 5 volts from grn/wht at PCM from control head whenever vehicle is not in Park--and mostly on when in any other gear.....nothing else in control head is amiss- beating on it does nothing. Whwn a/c is on, (not in park and foot on brake), I can turn on/off the 5 volt signal just fine with the a/c button. The 1996 U-van service manual I have clearly states that the a/c request signal goes to PCM and a parallel path the TCC circuit-- I will look up wiring diagram for it to compare to a 2001 U-van.

One of my issues is that I can't seem to get the face plate (facia) removed that covers the radio and control head- there are two 7mm screws beside cup holder- the rest snaps out- but there is evidently a screw or two behind the cupholder- and the cupholder refuses to come loose to remove it--the stop tab is extremely rigid- looks like it should bow down to remove- but it doesn't do it-- gee, I hate to break it loose...anyway, I tested at PCM input which should be just as good as control head output and I get the 5v signal there- just not when vehicle is in park-- which took me two hours to figure out- since no one usually test a/c circuits in anything other than Park.. I called the owner- he said his wife's biggest bitch was that when she'd start the car to cool it down while she was loading it- that it did not cool---since it was in Park- so we've confirmed that- I told him, I was going to test drive it- because I could not get a/c to come on- but it cooled fine when I pulled it in to my shop....there is something terribly amiss here.

Can anyone find a wiring diagram that relates a/c request signal to the park/neutral switch or to TCC circuit? - perhaps I'm getting a short to ground when in Park in a P/N switch. Foot on brake may be a factor as well..but not sure yet.

Anybody out there ever have one like this-- or is this just my lucky day!!!!


-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Wed May 23, 2012 at 9:33 PM by GM Tech

Metal Man on Wed May 23, 2012 9:38 PM User is offline

GM Tech

I'm no help with the ac only working in gear problem but i can tell you how to get the face plate off.

I just got done installing a new control head on a 04 venture that had shorted out. The one i was working on also had a small storage compartment below the cup holder that had to be removed. It has two 7mm screws holding it in. Next the face plate comes off.There are four 7mm screws holding the face plate on with three plastic tabs along the top. The two screws you have found and two more in the bottom. Pull the cup holder out far as you can. Then look up under the bottom. There way back there and hard to see but it has two more screws holding it in.Your basically gonna have to lay in the floor and look up to see them.

GM Tech on Thu May 24, 2012 9:44 AM User is offline

The plot thickens some more-- I decide to isolate the circuit-- cut the a/c request ( dk grn/wht) wire at the PCM-- now monitoring the a/c signal from control head with DVM I get:



In Park-- 0 volts

In Reverse- 12 volts

in overdrive - or 1,2,3,flickers between 12 and 0

so--I also connect a power supply set at 5 volt- to PCM input dk grn/wht - with dk grn/wht still cut away from control head--and a/c works continuously in all shifter positions-- no flaws--

So I have learned that the a/c request signal must be 12v- (as when Isolated and in reverse) and it is being pulled down to 5.4-6.3 volts even when it works in reverse -- looks like power supply could have been set at anywhere between 5 and 12v to enable a/c.....

I still cannot figure out relationship between control head and the Park position.....

The control head somehow knows when vehicle is in gear or park-- this is extremely repeatable- always 12v in reverse--always 0 volt when in Park- I've cycle it 50 times- always repeats- and follows the shifter position.--- there has got to be a relationship perhaps at park/neutral switch 2nd connector- which I haven't found a wiring schematic for...

I will figure this out- I will not replace parts without knowing why that relationship exists-

Almost acts like a bad body ground- can you tell me where control head grounds inside under dash--perhaps left kick panel?

-- but still why the differnce in voltage dependent on shifter location- unless they somehow share a ground and are grounding through each other


-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Dougflas on Thu May 24, 2012 10:04 AM User is offline

I should have a wiring diagram. Will check this eve when I get home. Do you have a fax # if I do have the schematic?

mk378 on Thu May 24, 2012 10:09 AM User is offline

When seemingly unrelated systems interact, it is very often a bad ground. Also you should check the voltage at the battery, and the main grounds under the hood. If the overall system voltage is excessive or not stable, various computers will go haywire. Though I think it may be a safe bet to just replace the control panel at this point.

mk378 on Thu May 24, 2012 10:10 AM User is offline



Edited: Thu May 24, 2012 at 10:10 AM by mk378

GM Tech on Thu May 24, 2012 10:18 AM User is offline

Okay this is new info--- I just unplugged the 4 pin connector on Park/neutral switch--(I left the bigger connector in place so I could start the car) and low and behold, I have 12v at all times and a/c function at all times- not dependent on shifter position!!!! But I notice park, P,N,O,3,2 indicators are inop on instrument cluster now-- so there is a relationship between instrument cluster indicators and HVAC control head-- can you please see if they share a ground and where it is at. ?...thanks-- OH BTW when I plugged connector back in at P/N switch now I have 6 volts in Park and Neutral-- but nothing in O,3,2--- so there is something amiss there- just farting with connector changed a few symptoms...


I lost my Mitchell -on Demand access- so this is why I'm losing it without schematics....

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

GM Tech on Sat May 26, 2012 11:09 AM User is offline

I nailed the MFer---the ground G113- on engine near starter was extremely corroded- the tranny position switch feeds off this ground to the PCM- this is why when the connector at P/N switch was unplugged all was fine..there is another ground wire along with this one that is probably the link to the whole trouble- but I don't have the ability to search it out G113...all I know that is when I pulled both wires off G113 and grounded them with a jumper- that everything was fine- so I cleaned up the entire ground point and now everthing works great- the mystery still remains as to what is the link between G113 and the control head a/c request signal.....I sure am glad I did not replace the control head as was suggested-- the control head ground was good at G200- although I cleaned it anyway.

If anyone wants to solve this- please provide the common link info at ground G113 on engine just above and to left of starter...

Thaanks again for all help provided by this forum.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

newton5 on Sat May 26, 2012 12:16 PM User is offlineView users profile

newton5 on Sat May 26, 2012 12:30 PM User is offlineView users profile

Hmm, lets try that again.

I recall something that might get you closer to solving the puzzle, although not an actual answer.
Many Ford products, starting in the early 90s, had a circuit between the radio and the Neutral Safety section of the Transmission Range Sensor. It was called a Mute circuit, as it muted the radio while cranking.
Often, a short would develop between the Neutral Safety section and Transmission Range input to the PCM. This would cause the radio to act exactly as you describe the AC clutch symptoms. On in Park or Neutral, Off in any gear.

I wonder if the tie-in is to disengage the AC clutch when cranking, or maybe during a manual downshift.

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