R134 undercharged?

Hi all, I just did a retrofit on my 91 Firebird. My compressor died and this is what I did.
Flushed the evaporator and condensor Put in a new compressor (harrison), new accumlator, o-rings, and a
variable orifice tube. Added 8oz of POE to various components, pulled a vacuum for 3 hours and held overnight.
The high side guage on the borrowed manifold set was broken, so I only have low side readings. system uses 2.25 lb or R-12, So I figured 28 oz or R134a. After adding two cans (24 ozs total). The low side pressure was 31. The duct temperature was 50degF. Ambient temp was 95deg in a garage in humid south florida. With the system off, pressure was 75. With the blower motor on high, a/c clutch would not cycle. accumulator was sweating, high side line just before orifice tube was very warm but not real hot. Am I undercharged? should I add another 4 oz. or leave it alone? Will it cause damage by being undercharged?
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If you are using 80% of the original charge then you should put in another 5 oz. and hope that the vacuum pump that you used pulled the system down to the correct micron level. That's pretty much all that you can do without more knowledge on the subject. Without having the tools that are at my disposal you really won't be able to tell if you have the correct charge. It's not rocket science but there is science involved in the correct way to repair and charge your system. I doubt even that most auto shops would do what I do to make sure a system is running correctly charged and efficient. Hope for the best.
I'm assuming that you repaird the leak in the system since you left it in a vacuum overnight. I can not stress enough the importance of repairing leaks in your a/c systems. Most failures of any type of a/c systems are the end results of poor maintainance and leaks. If the leaks or causes of failure aren't repaired then in a couple of months you'll just be back to where you are right now with a considerable amount of unnecessary wear to the components of your system.
Hope for the best.
...Ron -- 68' RS Camaro 88' Formula Bird
Some are wise and some are otherwise
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RSCamaro wrote:

Hopefully I repaired any leaks, thats why I replaced all the o-rings. Thanks for the response but, it doesnt really answer the questions. Am I undercharged? should I add another 4 oz. or leave it alone? Will it cause damage by being undercharged?
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you need 80%of 2.25 lbs. or 28-30 oz (28.8 to be exact)
: Hi all, : I just did a retrofit on my 91 Firebird. : My compressor died and this is what I did. : : Flushed the evaporator and condensor : Put in a new compressor (harrison), new accumlator, o-rings, and a : variable orifice tube. Added 8oz of POE to various components, : pulled a vacuum for 3 hours and held overnight. : : The high side guage on the borrowed manifold set was broken, so I : only have low side readings. : system uses 2.25 lb or R-12, So I figured 28 oz or R134a. : After adding two cans (24 ozs total). The low side pressure was 31. : The duct temperature was 50degF. Ambient temp was 95deg in a garage : in humid south florida. With the system off, pressure was 75. : With the blower motor on high, a/c clutch would not cycle. : accumulator was sweating, high side line just before orifice tube was : very warm but not real hot. : Am I undercharged? should I add another 4 oz. or leave it alone? : Will it cause damage by being undercharged? : :
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Although it probably doen't have anything to do with your problem, you should only use PAG. Do not use ester. GM has shown R4 compressor damage with the use of ester oils.
Beware of the 80% rule as it doesn't always apply. Consider a '93 Camaro's refrigerant system which held 2 lbs of R12.
A '94 Camaro used R134a but also required 2 lbs of refrigerant. I wouldn't hesitate to put the whole 2.25 lbs in.

Even though the sweating and 31 psi sounds like the vent temperature should be colder, I would say you are definately undercharged. A full charge would be closer to 36 ozs.

Add another can.
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David McNally wrote:

Wow, I did some research before the retrofit and never found anything suggesting Ester oil caused damage, infact everywhere I looked suggested POE.
I added half a can last night, at 85 deg ambient , I had 40 PSI. Blower on high, windows open. The low side was sweating almost all the way back to the compressor. Wouldn't that indicate too much R134a?
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First, I read the entire thread..... and no..I am NOT an advocate of 134a conversions....not with the replacements out there..
But...

What level vac did you pull? That would be my first question. Did you have a real pump, with a micron guage on it, or did you use the vac reading on the manifold, and was it calibrated correctly? Well..even if it WAS calibrated correctly, with no micron gauge, you are back at base one.

Useless..
You need both..

You need to only use 80% of the factory charge....period. I have never seen a car that would not cool that was R12 orginally, that would not work as well as it could on 134a at anything over that..

HUH? Your complaining? Thats an over 40F TD...and that was of course, with no fan in front to add some extra omph to the condensor..since all 134a conversions suck at idle, sitting still..

Nope..it wont..its just not gonna cool. Undercharge damage is prevented by the low pressure switch on the accumulator. If you add another 12oz, then you will be overcharged...and THAT will indeed create problems.....and since you had no high side gauge to read, well....you wont know what the head pressures are...

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