Can someone provide a guideline on what the high and low pressures should be. Summers here and I want to put the gauges on and check it.

Thanks~

 

r134a right?

 

I'm not sure on the correct tempature to do the calculations on this (and forgot the equasion as well)
But I have the sporlan chart here from my HVAC classes and can give you the PSIG if you want to do the math.

 

R134 is correct. I can do math...I think?
Send it and I will try.

The label states: Maximum charge weight - 2lbs, 6ozs.

 

The weighed charge will be the better way to calculate the total charge, since the temperature variables will affect your pressures. Unless you are just trying to "top off" the system, the best way to get an accurate charge is by weight in my opinion.

 

Yeah, there are 2 ways to charge a system, weight is the fastest.
You just load it all into the high side and start it up. (I could have that backwards)

With the other method figuring out high and low side pressures, you have to adjust the amount while the system is running.

 

And correct me if I am wrong (it sounds like you know your way around a cooling system) the pressure method is dependent on the OAT at the time you are performing the service. The weighted system, you just evacuate the system, (pull a good hard vac on it for a while if you really want to do it right) and then add the refrigerant by weight and you're done. The weight method IMO is a lot more foolproof since it doesn't take as many variables into account on the proper readings. It is different if you're working with a 30 ton chiller or something, but on the little A/C systems in our trucks, I think the weight method is a lot easier.

 

Weight method is easiest, yes.

If your doing the highside/lowside method, you have to measure the output tempature the system is putting out to fine tune it.

You take the sporlan chart and reference the output temperature, then you do some math to figure out the high side and low side numbers.

Then you fill up the low side and the high side (memory is really fuzzy on this) and start the system, and then use the pump in the system to build pressure while adding whatever refrigerant your using.
Then you need to test the output temperature of the system.

You'll be close using the system, but something like a refrigerator, you want it to be more exact, than .. lets say our trucks.

Plus you need to know the limits of the system.
Like a refrigerator, I was putting 5 lbs of r134a in them, our trucks only hold 2, but it all depends on how the system works.
Once you understand Hvac basics, you can work on any system unless they have specialty parts on them, but they all have 4 basic elements.

I took half of the HVAC classes in college and decided it wasn't for me.
So, I'm not a dummy on the subject, but some of the material I have forgotten.

Always, and I mean Always draw a vacuum before doing a system.
Always.
Anyone who tells you you can just add in r134 and be okay, they need a slap.
Air is a contaminate. Pulling a vacuum evacuates the system of dirt and water and air, which is what kills the systems and causes leaks or pump failures.

I shoulda brought my books with me when I moved down here to Tenn. I left them at home.

 

I do know all about vacuum, need to remove as much air as possible.

In this case - my system works OK, just want to check the pressures and "top it off", if needed.

Thank you!

 

With you being located in the SoCal Desert, I guess I can understand that!

Unless you're willing to evacuate your refrigerant and start over, you're going to have to throw a set of gauges on it and see what your pressures are. You'll need a set of gauges and the cooling chart, along with a way to measure the temperature of the system.

I have heard of guys just winging it and adding refrigerant a little at a time until the system starts to cycle on and off because it it overfull, then they let a little back out until the compressor stops cycling and call it a day. Not exactly a science, but I suppose it would work if you're willing to fiddle with it.

 

Could be just where it needs to be, but time to change the Refrigerant.

You'd get a better air charge from fresh 134. =)

 

I have a good set of gauges.

Read somewhere that the low s/b mid 30's, high 130-230.

 

 

R134a doesnt "wear out". Fresh or 200 years old its still going to be 134a. Find and fix your leaks that way your refrigerant doesnt get CONTAMINATED and lose its "Freshness" lol.

leaks will allow air into the system ESPECIALLY WHEN YOU PULL A VACUUM. thus contaminating your new refrigerant and the aforementioned "freshness"

 

Working pressure should be roughly 150 high side and 25 psi low side with the compressor running. Those pressure will vary with temp. Higher temp higher pressures, lower temp lower pressure.