air condioning pressure too low

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  #1  
Old 05-19-05, 01:54 PM
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Question air condioning pressure too low

I just recently retrofited my truck to an r134a system. Everything is working fine, except the pressure is only at 32psi on the low side and 175 on the high side. According to the charts this will only work for a 85 degree ambient temperature. I need to get above 200psi to make it work for the higher pressures that we are going to have this summer.

I believe that if I can put more freon that it will increase the pressure, however last time I tried it only took half the can and wouldn't take any more.

I heard an idea somewhere that spraying water on the evaporator would help to take in more freon. Anybody Know if that is a good idea.

Also I was toying with the idea of running some fans in front of the condensor.

Can anybody offer some advice?

Thankyou in advance.
 
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  #2  
Old 05-19-05, 03:54 PM
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If you're charging as a gas (like I believe is supposed to be done with r-134a), it will help to put the refrigerant can in a warm container of water. Once the temp of the can drops below the boiling point of the refrigerant, the flow will stop out of the can.

If you're a little more daring and you're charging as a liquid, then just bumping the idle up on the engine will work.

What was the ambient temp outside?

I'd say you're a little undercharged. (Guessing)

Doing anything to alter the 'natural' temp of the condenser will throw off your pressure readings for accuracy of charging. An automotive system is properly charged by weight and not by pressure. Unless you're going to have water running on your condenser all the time you don't want to measure the refrigerant charge by pressure that way.

It’d be best to take the factory recommendation for the r-12 charge and drop that by 75-80 % (Depending on how heavy-duty your cooling system is). Then you can charge by weight no matter what the ambient temp is and you’ll be good to go.
 
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Old 05-19-05, 08:16 PM
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Thansk for the reply.

I believe the ambient temp was around 78 - 82 on the day I did the job.

How warm should that water to submerge the can be?
 
  #4  
Old 05-20-05, 06:29 AM
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The water can be any liquid temperature.

The boiling point of r-134a is below zero (F). You could actually use cold water and it'd work, but if you use warm / hot water it'll last longer before the can of refrigerant starts to freeze the water. Check the temp of the water once in a while and replace it before it does freeze.

I'd say to keep the water under 120 (F); that's usually the warning limit on aerosol cans.
 
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Old 05-20-05, 10:49 PM
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Check your pressures under the following conditions outside ambient 80f or above AC set to MAX cool set the blower to its highest setting open the doors wide open and windows down rev the engine to about 1500 RPM. Now post your truck model and year plus the low and high side pressures and ambient temp and I can let you know if you are close. The warm water bath for the refrigerant can works well just do not get carried away with the water temperature you don't want the little can turning into a bomb. Hopefully you flushed the system/changed out the drier/added oil and vacuumed the system as part of your retrofit procedure right?
 
  #6  
Old 05-22-05, 03:46 PM
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Why hello all, thanks for the advice.

Yesterday I tried the water trick. and that seemed to do it. I put the can upside down in bucket of warm water, and took the engine to 1500 rpms. It took a few minutes but all of a sudden the low side pressure went up to about 60psi. It then backed down to around 40psi. After the can was empty I closed the low side and took off the can then I opened the high side and got an immideiate jump to 275psi. Inside the cab the temperature was dropping very quickley.

This is the real kicker the ambient temp was a balmy 95.6 deg F.

I believe that now I can handle some higher temps than the charts I have seen showed.

I did flush the system and vacum it out. Everything that needed to be changed was. And now the system is working nicley.

I am thinking about putting a pusher fan in front of the evaporator core just to help at the idle.

1986
F150
5.0FI
198,000 miles
FS-6 compressor



Thanks for all your help everybody.
 
  #7  
Old 05-23-05, 02:27 PM
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The pusher fan will help.

Be careful with charging r-134a as a liquid. You can ruin your compressor if too much liquid reaches it. I always charge as a liquid (I know, not recommended) and I never have to use warm water. 1500 RPM doesn't sound too bad, and the water likely had almost no effect on it charging faster as a liquid.

The water trick should only be necessary if you are charging as a gas. Then you're only letting gas out of the can and making it so that any further refrigerant coming out of the can must first boil off from the liquid in the can. (Which is how a/c works, it makes the can cold by absorbing heat to boil the refrigerant off.) The water is there to keep heating the refrigerant so that it doesn't fall below the boiling point (somewhere around -11 F I believe).

If you're charging as a liquid, then there's no boiling of refrigerant in the can, it's just squirting liquid in the system. Hopefully to mostly boil off to a gas before it reaches the compressor.
 
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Old 05-24-05, 08:07 AM
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placing the can in warm water raises the pressure inside the can the pressure inside the can needs to be above your low side pressure to be able to get most of the freon out of a can, higher pressure inside the can will be able to push out more freon regardless of whether you are charging as a liquid or gas.
charging as a liquid is commonly done when engine is running it is usually recomended to only crack the low side open enough that the low side pressure will only increase by 5- 10 psi this adds the liquid slow enough that you do not have to worry about compressor lockup.
 
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