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Username Post: A6 ac compressor        (Topic#376287)
Hwilliams 
Newbie
Posts: 19

Loc: South carolina
Reg: 08-21-21
01-26-25 11:06 AM - Post#2877417    

I have a 1968 impala with factory air conditioning.I’m converting to r134. The previous owner stated that it was working 4 years ago when I purchased it. Rebuild the motor last year, now it’s time for the ac. I vacuumed the system down it holds a vacuum. It took one can and stopped. It still has pressure in the system. For some reason I’m not getting power to the compressor, I traced the green line to the sensor on the box no power. No power from the brown wire coming in. Line runs to firewall. Do anyone know where it gets it power from.



 


Hwilliams 
Newbie
Posts: 19

Loc: South carolina
Reg: 08-21-21
02-01-25 03:06 PM - Post#2877564    
    In response to Hwilliams

No one has any knowledge of ac system



 
toro455 
"9th Year" Gold Supporting Member
Posts: 1517
toro455
Loc: Western NY
Reg: 06-15-02
02-01-25 03:38 PM - Post#2877565    
    In response to Hwilliams

I don't have factory original AC in my car so I didn't think I was the best to reply... That said you wrote that you put one can in and the compressor isn't getting power. Some systems have low pressure cut outs. I guess that your system needs likely around 2.5lbs. It was very good you evacuated it but with only 1 can you are still at what would be considered low charge. I wonder if it's so low that the compressor won't come on.

Does the AC have a separate fuse? When you move the control to AC mode I assume the power triggers a relay. Is there power coming to and from the switch? Can you sense power at the relay for the signal wire coming from the switch? If yes do you hear the relay click on/off when you move the AC switch? Assuming the supply wire is positive, is the higher amperage source wire hot at the relay? I don't know the wire colors but those are some of the things I would check.

Unfortunately it seems there isn't a great FSM for 68 Impala. As I know we are stuck with the Fisher Body manual and the factory assembly manual. I was able to find a seller on eBay with a very nice coloring wiring diagram but I lost it and at this point I suspect it will only appear once I've already purchased a replacement.. Getting something like that may help.

It may as well help if you comment as to whether or not you have the Comfortron automatic system or just the standard AC control head.



 
bobb 
Super Senior Member
Posts: 6921

Loc: paradise
Reg: 09-05-03
02-02-25 09:42 AM - Post#2877575    
    In response to Hwilliams

when i come across an unused system i hot wire the compressor to see if the system even works. that way i know in advance if there are bigger problems lurking.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
aghaga 
"4th Year" Silver Supporting Member
Posts: 2392
aghaga
Age: 70
Loc: Woodlawn, Va.
Reg: 07-05-08
02-03-25 06:25 AM - Post#2877607    
    In response to Hwilliams

Disconnect the wiring from the low pressure switch and attach a jumper between the two connecting points in the wiring. You can make a jumper out of a short scrap piece of wire striped on both ends. This will energize the compressor clutch until enough refrigerant is in the system to satisfy the low pressure switch, usually 2 cans. Remove the jumper then and reconnect the low pressure switch wiring.



 
Hwilliams 
Newbie
Posts: 19

Loc: South carolina
Reg: 08-21-21
02-03-25 02:57 PM - Post#2877616    
    In response to aghaga

Finally had time to troubleshoot. Traced line to firewall then it disappears. I can’t see where it goes due to air box under the dash, I took out the switch, and it’s getting power and sending power out. The compressor get its power from the thermal switch, which gets it power from a diverter door sw per diagram. I haven’t located that yet. I don’t think this system have a low pressure switch because I can’t locate one nor do I see one in the assembly manual. I researched that there was a compressor circuit 2 terminal button switch that activates the ac, on top of heater box under the dash which is depressed when the levels are positioned to activate the compressor for ac. I still have to locate that also. I have the manual ac not comfortron also. The compressor engage if jumped from battery



 


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