A/C CHARGE PRESSURE

[MIDNIGHT RIDER]

On a stock 1985 diesel factory-A/C system with R134a conversion, 90* outside temperature, engine OFF, what should the equalized system pressure of a properly charged system be ??

Many thanks.

 

[junk]

I'm not sure, but I would expect it to be around 70PSI or slightly higher. That's what I've seen when working on my own cars. I'm not sure if this is a good measure, but just my observations.

 

[FordGuy100]

Looking at a pressure chart, R134a should have a pressure of around 105 psi at 90*F

http://www.google.com/imgres?imgurl...OFYecrgHc3YHICQ&sqi=2&ved=0CDcQ9QEwAg&dur=478

 

[firehawk]

Don't trust those numbers. If you have an a/c issue, you need to know the numbers while it is running, high and low. Do things the correct way or don't bother.

 

[MIDNIGHT RIDER]

Don't trust those numbers. If you have an a/c issue, you need to know the numbers while it is running, high and low. Do things the correct way or don't bother.

I know the numbers running, both high and low; I also know what it currently reads when engine OFF and system equalized.

What I need to know is what the equalized system pressure is on a properly working, properly charged R134a system in one of these trucks.

Providing the outside temperature and barometric pressure is the same, that pressure should be the same on all properly charged trucks of this vintage, just like proper inflation of a tire, and should be a base-line from which educated decisions can then be made as to just what may or may not be going on.


Thanks for reading.

 

[FordGuy100]

What is your running pressures?

 

[PackRat239]

There is no such thing as properly equalized pressure when off. it could land anywhere, and has no value. the running pressures are all that matters.

 

[chris142]

The equalized pressure will be the same regardless of wether it has 2oz in it or 2 lbs. Dont mean a thing really. need high and low readings to diagnose AC problems.

 

[Sw1tchfoot]

There is no such thing as properly equalized pressure when off. it could land anywhere, and has no value. the running pressures are all that matters.

The equalized pressure will be the same regardless of wether it has 2oz in it or 2 lbs. Dont mean a thing really. need high and low readings to diagnose AC problems.

I'm not sure if you guys mis-understood him or if i'm just stupid. When the a/c compressor is not running the pressure is the same (equalized) on both the high and low pressure sides. As the content of the system increases, the pressure increases and the pressure with 2lbs will be significantly higher than with 2oz. Given the same ambient temp, elevation, atmospheric pressure, etc would net the same system content if the system has the same capacity at an equal pressure reading.

 

[chris142]

Sw1tchfoot. That would be correct if using air. Refrigerant pressures do not change if you add or remove refrigerant to a system thats not running. Once the pump is pumping and you have a restriction like an orifice tube or expansion valve only then will you have a different pressure

Refrigents are a strange chemicle.

 

[chris142]

So if you had a car with 2 oz in the system and had say 100psi in it with the ac off and you added say 2 lbs more to it you would still have 100 psi in the system with the ac off.

 

[firehawk]

If you have good running numbers (which we don't know), why would you care what the non running numbers would be?

 

[MIDNIGHT RIDER]

I'm not sure if you guys mis-understood him or if i'm just stupid. When the a/c compressor is not running the pressure is the same (equalized) on both the high and low pressure sides. As the content of the system increases, the pressure increases and the pressure with 2lbs will be significantly higher than with 2oz. Given the same ambient temp, elevation, atmospheric pressure, etc would net the same system content if the system has the same capacity at an equal pressure reading.

Thanks for reading and understanding my question.

It seemed like a reasonable question and makes sense to me.


I bet if one checked every same-model vehicle as it came straight off the assembly line, the equalized system pressure would be almost exactly the same.

I bet that on the assembly line, these systems are charged without the engine running.

Thanks.

 

[xcite]

Yes the systems are charged while not running, but they are charged with a volume reading not a pressure reading. Ex a system will be charged with 2 lbs of charge and system final pressure is not even looked at.
All that matters is how the running pressure vs temp out dash compare in order to know system is operating properly. Static pressure of system is not a good indicator of proper charge.
I have been do AC work over 20 years dont try to over think it.

 

[xcite]

To state this alittle clearer when I say 2 lbs of charge I mean it in weight not pressure.