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#1 |
Registered User
Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Factory A/C question, '72 GMC
Good morning--
I am wondering if anybody can tell me if my '72 with factory air has a low pressure switch that would keep the compressor from kicking on. The compressor kicks on fine but I don't want to run it too long if it is low on R-12. Which brings me to my next question... I found one A/C port on the '72 last night but could not find the second. I believe I found the low side port. If anybody could tell me where the second port is, I would appreciate it. The truck is stored at a friend's house and we didn't have good light to look under the hood so it may have been right under our noses. Anything different about charging these systems compared to other vehicles? I've charged both R-12 and R134A systems in the past. Pretty straight-forward. Thanks, Mark
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#2 | |
Registered User
Join Date: Feb 2000
Location: Center City, MN, USA
Posts: 3,254
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Re: Factory A/C question, '72 GMC
Quote:
My 1971 Chevelle with the same factory AC does NOT have a thermal limiter. When I added factory air to my truck I did NOT add a thermal limiter but on my list of things to do is to find a wiring harness with that in the AC circuit. To find if you have a thermal limiter in your truck, follow the green wire on the compressor. If it simply goes back through the firewall you don't have one. I'm guessing you don't.
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'70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN |
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#3 |
Registered User
Join Date: Aug 2004
Location: Oakville, MO
Posts: 1,018
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Re: Factory A/C question, '72 GMC
There should not be a thermal limiter on these trucks. Compressor runs constant whe the system is turned on, POA valve controls refrigerant flow.
Low side port is on suction line just before the POA valve (sort of above the evap coil box on firewall) High side port is on liquid line muffler over the top of compressor. I would not convert this system to 134a, but that is just me. |
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#4 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Thanks Tim. I'll check it out. I have no plans to convert from R-12. My '93 Toyota Land Cruiser is R-12 and I chose to leave it alone. R-12 is expensive but can be found fairly easily. Blows very cold too.
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#5 |
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Re: Factory A/C question, '72 GMC
if you have no leaks and no need to replace expensive components i would stay with r-12. it is expensive, but easy to find as stated, and it will freeze you out of the cab on the hottest day. the clutch bearing is finally starting to give out on my a-6 compressor and i am going to replace/upgrade with a pro6ten compressor from old air products, and staying with r-12.
Posted via Mobile Device
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1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man |
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#6 |
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![]() Join Date: Jul 2009
Location: Tucson, AZ
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Re: Factory A/C question, '72 GMC
Mark, I also have a '72 GMC with factory air and absolutely do not have a high pressure port. If there was one on it originally, then a PO must have replaced it with something non-stock. I just watch for the flow of bubbles to stop in the window of the dryer to determine when to stop adding refrigerant. Seems to work fine.
Mike Mileski Tucson, AZ |
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#7 |
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Join Date: Aug 2010
Location: Edwards, CA
Posts: 7,503
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Re: Factory A/C question, '72 GMC
Mark,
It looks like you are going to be putting a factory service manual to good use!
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Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID ** Blazer SPID ** Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders ** Do you have a 1972 Plaid Pickup? ** Plaid Blazer ** Plaid Suburban |
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#8 |
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Join Date: Aug 2010
Location: Edwards, CA
Posts: 7,503
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Re: Factory A/C question, '72 GMC
Mark,
It looks like you are going to be putting a factory service manual to good use!
__________________
Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID ** Blazer SPID ** Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders ** Do you have a 1972 Plaid Pickup? ** Plaid Blazer ** Plaid Suburban |
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#9 | |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
Quote:
--Mark
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#10 |
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Location: Anton, Texas
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Re: Factory A/C question, '72 GMC
harrydunn: the compressor on your truck should have an oil sump, it was called the a6 i believe , the newer ones dont have this, and have to have oil and freon going through the system , you could run it and check the freon level without worry of hurting the compressor , also if its out of freon you can check and add oil to the sump, before charging, the bottom of the compressor will have a bolt you can remove and use a oil can with the right compressor oil and fill it up...hope this helps...
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#11 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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**UPDATE** Re: Factory A/C question, '72 GMC
A few questions.
1) Loosened the compressor sump plug and there was pressure inside. Normal? I tighened it back up without checking so I could post on here first without opening it all the way up. 2) Compressor is engaging so added a can of R-12 I had laying around. A/C line running into the firewall box was ice cold as I would expect but I never got any cooler air out of the cab vents. I'm all ears!
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#12 |
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Location: Anton, Texas
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Re: Factory A/C question, '72 GMC
harrydunn: can you take a lot of pic's of all the a/c under the hood, all hoses, black box, compressor, every thing....maybe we can locate a high side hose connection and get some pressure reading on your system, that would tell us alot of what is going on in the system...also pics of the the condenser and rad. area....are both heater hoses very hot.....if so for right now plug them off.....and see if it gets colder inside....its to dang hot not to have an a/c not blowing cold air....
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#13 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
Took some photos but here is a video first. Let me know if you think some photos would help and I can post those too. Please note that the compressor is off for the first part of the video. It had been engaged but I turned it off right before I started shooting the video.
Thanks.
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport Last edited by harrydunn; 07-01-2012 at 11:06 PM. |
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#14 | |
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Join Date: Feb 2000
Location: Center City, MN, USA
Posts: 3,254
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Re: **UPDATE** Re: Factory A/C question, '72 GMC
Quote:
If "A/C line running into the firewall box was ice cold as I would expect" is true, your AC is working, you just need to figure out how to get that cold air in the cab. It could be the heater is on and/or 40 years of mouse druff is blocking efficient exchange of air in the system. FWIW, my system is a cobbled together stock system. I didn't bother to get a heater control valve thinking I would wait until I knew it was all working. I simply plumbed a ball valve into one of the heater hoses. Valve is closed now. I'll open it this fall for winter. If you aren't sure if the shut off is working or not, you could put in a temporary manual valve and shut it off. I would do that before I started drilling holes.
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'70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN |
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#15 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
Good stuff here. Will definitely check it out.
Tim-- The evap boxes on these are a split design. Would you not be able to undo the bolts holding each half together and crack it open?
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#16 |
Registered User
Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
Good stuff here. Will definitely check it out.
Tim-- The evap boxes on these are a split design. Can you unscrew the bolts holding each half together and crack it open? ![]()
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#17 |
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Location: Anton, Texas
Posts: 2,364
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Re: Factory A/C question, '72 GMC
man...i cant see that fast.....slow way down....lol what i could see ..it looks like you have a new hose on the back of the compressor , like a made up one , not factory that may be where your valve went, they made a hose with out the valve. if you can take some still pic's of it and post....
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#18 |
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Join Date: Jan 2010
Location: Here
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Re: Factory A/C question, '72 GMC
not to hijak but i added this switch to my 67 when i went thru the a/c. is this some kind of thermal limiter? it shuts the compressor off below 28 and above 380 psi. just had to wire it into the green wire that goes to the compressor. Rod.
http://www.ebay.com/itm/400288128124...84.m1423.l2649 |
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#19 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
Some photos I took this afternoon. I'll have to get some photos of the back of the compressor tomorrow...
http://s1065.photobucket.com/albums/u395/darryhunn/
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#20 |
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Location: Anton, Texas
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Re: Factory A/C question, '72 GMC
in pic # 6 is that not a valve cap in the line at the back of the compressor?
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#21 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
I've seen that before and it is definitely a cap to the system but it does not seem to be the correct size to screw an A/C hose to it. What does the fact that the hose downstream of the orifice tube is ice cold telling me? I know it's supposed to be cold so I'm assuming my orifice tube is fine and not blocked/broken?
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#22 |
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Location: Anton, Texas
Posts: 2,364
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Re: Factory A/C question, '72 GMC
looking at the pic of the receiver dryer the little window looks like the inside of your system may be contaminated ... your dryer may be coming apart inside...the window is turned brown looking, a good sign it needs to be replaced, also you need to flush out the complete system when you replace the dryer .even the valves and lines at the black box....that is where i would start, it kinda hard to tell from miles away, pressure reading could help a lot in really seeing what going on inside the a/c system....maybe some one else has some better ideas....this is what i saw....good luck on the a/c fix....its hot out side.
Last edited by ole dollor; 07-02-2012 at 06:55 PM. Reason: spelling |
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#23 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
I appreciate the assistance. I probably won't worry about it too much as it's not my daily driver. Just one of my toys. It would be neat to get it working again though.
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#24 |
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Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
How difficult is it to see if the blend door is working correctly? I popped my head under the dash last night and verified that the cable is connected to the 'COLD' rod on the dash HVAC panel but could not verify if the blend door was actually working correctly.
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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#25 |
Registered User
Join Date: Dec 2010
Location: Columbia, MO
Posts: 256
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Re: Factory A/C question, '72 GMC
After confirming that the section of high-side hose containing the service port and muffler has been replaced at some point in the truck's life, I was only able to get a low-side reading, unfortunately. Static pressure reads 80 psi and, with the compressor kicked on, 30 psi. The pressures are a bit low but should not be responsible for the absence of cold air out of the vents I'd have to say. Tube past the expansion valve is ice cold so I would assume I have some sort of blockage in the evaporator or a blend door problem.
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1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport |
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