71 AC question? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

myyamr7 · 07-13-2013, 01:48 PM

I'm working on getting my AC system working again after having the truck apart. I bought it over the winter, so I never bothered to try and turn it on. The system at the time, was complete and had a charge.
Just because it was apart, I replaced all the lines and hoses, compressor, dryer and a few other minor parts.
I have an appointment next week to get it charged, but when I was hooking everything up, the compressor kicked on? There is no charge in the system at all. After a little messing around under the dash, I found it would only kick on when I turn the fan on? I figured it was the AC fan relay, so I replaced that with a new one. Same thing still happens.
I hate to keep tossing parts at it playing the guessing game, does anyone have any idea what could cause this? AC relay itself? Dash Control switches? or does it just need the charge for the system to work correctly all together?

Thanks in advance for any help

TchncnDen · 07-13-2013, 02:08 PM

I'm in process of doing my ac now also. These systems were designed for the compressor to always be on, no cycling. What you're seeing is normal.

myyamr7 · 07-13-2013, 03:52 PM

Even with no charge in the system, the compressor will start?

TchncnDen · 07-13-2013, 04:15 PM

Yep, the compressor is direct wired as being on, it doesn't have any feedback to charge pressures. This one had me stumped for a bit as well. Basically (very basically) there are internal valves that open and close based on pressure. With the valves open it is a freeflowing system. A freeflowing system has no pressure so there is no need to cycle the clutch, the compressor starts any time the air is on.

Daddy'O · 07-13-2013, 04:25 PM

Sounds like your AC compressor switch could be stuck in the on position. This switch is controlled by a cable from your AC/Heater controller. The switch is located behind the diverter box under the dash.

myyamr7 · 07-14-2013, 12:44 PM

Quote:

Originally Posted by Daddy'O

Sounds like your AC compressor switch could be stuck in the on position. This switch is controlled by a cable from your AC/Heater controller. The switch is located behind the diverter box under the dash.

Thanks, I'm going to check that now.
I think there may be other issues as well, for some reason with everything plugged in, the blower fan comes on even if there truck is off, with no key in it. I unplug the 3 wires from the AC relay switch, and the fan works normal again.....won't come on with the key off, but once the key is turned on, it works as it should. It seems like something is getting direct power from somewhere?

07-13-2013, 01:48 PM	#1
myyamr7 Registered User Join Date: Dec 2012 Location: Providence, RI Posts: 211	71 AC question? I'm working on getting my AC system working again after having the truck apart. I bought it over the winter, so I never bothered to try and turn it on. The system at the time, was complete and had a charge. Just because it was apart, I replaced all the lines and hoses, compressor, dryer and a few other minor parts. I have an appointment next week to get it charged, but when I was hooking everything up, the compressor kicked on? There is no charge in the system at all. After a little messing around under the dash, I found it would only kick on when I turn the fan on? I figured it was the AC fan relay, so I replaced that with a new one. Same thing still happens. I hate to keep tossing parts at it playing the guessing game, does anyone have any idea what could cause this? AC relay itself? Dash Control switches? or does it just need the charge for the system to work correctly all together? Thanks in advance for any help __________________ Mark 71 C10 Cheyenne 12 Aprilia RSV4

07-13-2013, 02:08 PM	#2
TchncnDen Registered User Join Date: Apr 2012 Location: Denver, CO Posts: 232	Re: 71 AC question? I'm in process of doing my ac now also. These systems were designed for the compressor to always be on, no cycling. What you're seeing is normal. __________________ Another 71 My truck In tank fuel pump how to LS factory gauges wiring how to-post 18

07-13-2013, 03:52 PM	#3
myyamr7 Registered User Join Date: Dec 2012 Location: Providence, RI Posts: 211	Re: 71 AC question? Even with no charge in the system, the compressor will start? __________________ Mark 71 C10 Cheyenne 12 Aprilia RSV4

07-13-2013, 04:15 PM	#4
TchncnDen Registered User Join Date: Apr 2012 Location: Denver, CO Posts: 232	Re: 71 AC question? Yep, the compressor is direct wired as being on, it doesn't have any feedback to charge pressures. This one had me stumped for a bit as well. Basically (very basically) there are internal valves that open and close based on pressure. With the valves open it is a freeflowing system. A freeflowing system has no pressure so there is no need to cycle the clutch, the compressor starts any time the air is on. __________________ Another 71 My truck In tank fuel pump how to LS factory gauges wiring how to-post 18

07-13-2013, 04:25 PM	#5
Daddy'O Registered User Join Date: Jan 2012 Location: Whitesboro, Texas Posts: 932	Re: 71 AC question? Sounds like your AC compressor switch could be stuck in the on position. This switch is controlled by a cable from your AC/Heater controller. The switch is located behind the diverter box under the dash. __________________ Cheers - Wayne Our Shop Build - http://67-72chevytrucks.com/vboard/s...d.php?t=620966 '55 Wagon Build - http://67-72chevytrucks.com/vboard/s...d.php?t=689157 1971 Cheyenne Super Ochre/White LWB 350 Auto - my son's truck "Nancy" 1972 GMC K2500 Custom 4X4 Olive LWB 400 SB 4-speed -"Greenie" - Restoration to begin after the '55 Nothing sucks more than that moment during an argument when you realize you're wrong.



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