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Help me out... charging my system.

jntmjt1 on Wed April 21, 2010 9:28 PM User is offlineView users profile

Year: 1966
Make: Pontiac
Model: Bonneville
Engine Size: 389
Refrigerant Type: R12
Ambient Temp: 60
Pressure Low: 35
Country of Origin: United States

I don't know what I'm doing, but I'm determined to get it right! I have a 1966 Bonneville with the original A/C system. It uses R12 and about every 4 years it need a refill. This time, I decided I'd try to do it myself, and I need some help.

Yesterday, I hooked up my gauges and shot 2 cans of R12 in the system. The outside temp was about 65 degrees, I had the cans of freon in a pan of warm water to give them a boost. The first can, I was reading something like 30 on the low side and 50 or 60 on the high side. After the second can, I was at about 30 on the low side and 100 on the high side. I was getting cool, but not cold air out of the center vent.

Since the high pressure climbed as I added freon, my assumption was I needed more freon (I thought it should be around 160), but I was out of daylight so I called it a night. Today, I was prepared to give it some more freon, and I started the car and hooked up the gauges. I was at 30 on the low side and 25 on the high side, then I noticed frost building up on the aluminum line on the low pressure side of the expansion valve (between the expansion valve and the evaporator). The air was still blowing cool just like yesterday. After I shut the car off, my low side gauge went up to about 70.

So what is going on? Why the big difference in the high side from yesterday, but no real difference at my vent temp? What have I done wrong, and how do I fix it?

Thanks for your time,
John Thomas
[email protected]

Edited: Wed April 21, 2010 at 9:36 PM by jntmjt1

Chick on Wed April 21, 2010 10:30 PM User is offlineView users profile

Each time you top it off, you can possibly add air into the system, why not try to find the leak and fix it..?? Then pull a deep vacuum and recharge the factory amount back in.. Are you using R12 or something with the words R12 in it..Like freeze 12?? Was dye ever added during these top offs?? are you gages calibrated? if the underhood temps were the same as the outside air temps, 70 psi could indicate air in the system.. But it should be done right..recover, fix the leak and recharge...

Email: Chick


Freedoms just another word for nothing left to lose

jntmjt1 on Wed April 21, 2010 10:49 PM User is offlineView users profile


Thanks for the info, but... I am using genuine R12, not freeze 12 or anything like that. The reason I'm not fixing the leak is the problem is in my evaporator and on the 1966 Bonneville, it is virtually impossible to remove. The sheet metal inner fender has to come completely out of the car before I can even begin to tear into the a/c box. If the leak were worse than needing a recharge every four years or so, I'd consider it, but I can't justify going there at this point.

My gauges are good to go, they are a good quality set, not the Harbor Freight stuff. There is dye in the system, but none that I ever added; it's been in there for years. When my a/c is topped off right it will run you out of the car, and it is a giant station wagon with a black vinyl interior. It blows that icy looking vapor out of the center vent. I just don't know how to get it back to that. My old mechanic used to get it there, but I've moved and don't have his assistance anymore.

I don't understand why air in the system would make the low side climb to 70 psi only after I shut the car off. Also, the underhood temp was certainly warmer than the outside temp.

What would cause the frost on the line to the evaporator? and why the big difference on the high side from yesterday to today?

NickD on Thu April 22, 2010 5:20 AM User is offline

Recall having to remove the front bumper and right front fender on my 70 Buick just to repair the blower motor. You do what you have to do. Spent more time drilling out rusted in bolts with broken off heads than anything else. Do you really need a right front fender and a bumper? Well the fender held the head lamps.

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