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AC Pressure


power453's Avatar
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03-19-05, 08:02 PM   #1  
AC Pressure

Hey every body, Today I finaly got around to getting the air condiionter on my truck working again. I rebuilt the compressor with new shaft seals, new orings all around, new orfice tube, new accumulator, and I vacuuemed and charged it up. I got the low side pressure to around 40 PSI and the high side at 205 PSI.

Is that pressure normal or do I need a another can of freon?

By the way I did a conversion from r-12 to r-134a.

The system is cooling well enough, although It only reached a high today of 78 today.

Some Advice Please,
R. Ellis

 
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Kestas's Avatar
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03-20-05, 05:09 AM   #2  
It sounds like you did it right. I usually look at the vent temperatures to determine success. Anything below 40 (depending on the outside temperature) is considered success.

 
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03-20-05, 08:11 AM   #3  
The high and low side pressures are not really an indicator of a under, or overcharged system. YOu need to put in exactly what the label under the hood says the system holds, if anything, slightly less. PUt a thermometer in one of the outlets in the dash and run the fan on high. A 78 degree ambient should provide approx. 45 degree outlet temp, assuming the humidity isn't too high. Humidity actually makes a/c systems work harder.

 
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03-20-05, 09:08 AM   #4  
Thanks I will try those suggestions.

So If it is not as cold as it should be do I just add another can? Or is there somehting else wrong?

 
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03-20-05, 09:42 AM   #5  
When converting from 12 to 134, put in about 80% of the weight of R12 required. If your system called for 2 pounds of R12, install about 1 pound 10 ounces of R134a.

Due to molecular weight differences, 2 pounds of R12 takes up less room than 2 pounds of R134a.

HTH

 
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03-20-05, 01:55 PM   #6  
In the Texas summers, Mr. Ellis may not be happy with 45 vent output at 78 ambient. He needs to maximize the system.

The other posters gave good advice. 80% of the r12 charge is what you should aim for. This is a rough estimate. Pressures only give you a rough idea of what is happening. Charging should be done with the doors and windows open, blower fan on high, thermometer in the vent, and a garden hose misting the condenser on front to keep the compressor head pressures down. Charge until the vent temperatures don't drop anymore. The accumulator will hold any excess charge (to a point). The vent temperature should flatline. At about the same time, the line from evaporator to compressor should start getting cold. These are the clues one looks for to obtain optimal charge. Any excess charge will buy some time should some of the refrigerant weep out over time.

 
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03-22-05, 04:25 PM   #7  
Hey thanks everybody. I put a thermometer in the vent and it got down to about 53 degrees F. It also takes a signifigant amount of time to let it get that cold, around 15 to 20 minutes.

I had a thought I would run by everyone,

If a newer vehicle has R134a as standard, then the compenents are to be tougher and compress better, and Ideally cool better. I was thinking about going to a junkyard on another ford truck that already has r134a components similar to mine and getting its components and installing them on mine. Maybe with some minor modifications for the compressor. Does anybody think this is a good idea?

Thankyou,
R. Ellis

 
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03-23-05, 05:48 AM   #8  
I don't think you'll gain much from a newer donor vehicle. The only exception would be the condenser. Converting to r134 - at least by design - requires a beefier condenser because of the inefficiency of r134 when compared with r12. I'm not sure how critical it is for Ford vehicles when converting. I think Ford converts better than others.

53 isn't that great. You should be able to do considerably better. Have you tried charging more refrigerant? Did you vacuum well before charging?

 
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03-23-05, 01:09 PM   #9  
I did vacuum out the system. It held the vacum for twenty mintues with the pump on. Then quite a while with out the pump on. Then I charged with as much as it would take. It only took about 3 cans. I couldn't make it take any more.

 
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03-24-05, 05:43 AM   #10  
There's something wrong that I can't put my finger on. Let me refer you to two popular web sites devoted to automotive a/c. There are many professionals that volunteer their time helping people such as yourself. Post your question there, you should get some good answers.

aicondition.com

ackits.com

There, you'll also find links to parts and tools you may need.

(Disclaimer: I have no commercial interests in these sites. I'm just a satisfied customer.)

 
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