I have all of the equipment to evacuate and charge an R134 system. Most of the material I have read talks about specific weight of R134 for a specific system. However, my bus dash AC system is unique and must be charged by the gages. I have read that using gages for R134 is much more "tricky" than for R12.
When I first installed my dash air system, it was hot outside and I was careful to make sure the high side did not get too high (based on what little information I could find). I developed a small leak at a loose fitting and lost some of the charge. I went to use the AC side of the heater/AC to defrost (de-humidify) the air on a rather cold day a couple of months ago and it did not provide the needed AC.
I waited for the outside temperature to get into the 50's and tried to recharge. However, the reference material I have warns you to be careful of charging at low ambient temperatures.
I really need a good reference "manual" for doing "custom" AC charging (preferably something on-line). Anybody got any suggestions?
Jim
Hi Jim,
There is good refrence charts. I'll have to find one that I can e-mail you or paste.
However, R-134A is a blended gas. Which means when you loose some, you may be loosing more of one gas then the other.
Depending on how much you lost, Half or more I would advise you to reclaim it all and recharge with new. Less then a 1/4 you may get by
with no issues by just adding to the mix. It's always better to know how many lbs and ounces your system holds but by using guages you
can get close with a chart.
Nick-
Jim, try this chart.. Just keep a eye on the suction line so that it doesn't start freezing back to the compressor.
http://www.csgnetwork.com/r134apresstempconv.html
Hello Go to the carriier transicold site for service. you will find all kinds of info about servicing carrier systems in buses.. you will find a system very similar to your system. Also Carrier has service info for the techs especially spring checkup stuff that is right on for what you are doing..
They also have installation and startup notes which can be used and checksheets for the temp and pressure measurements. You can use one of your temp systems to get inside temps exit and entry from your evaps; that with the head pressures and the notes will get you where you need to be.
Happy Bussin Mike
Nick, thanks for the link. I was hoping to get something a bit more how to do with the manifold and gauges.
Mike, I poked all around the Carrier Transicold site and could not find anything on basic system charging. I downloaded several manuals and they all refer to charge by weight or use of site glass. Perhaps I did not poke around in the right place.
What I am looking for is AC tech 101 where it tells about checking system charge with the gauges and charging the system with gauges (not by weight or site glass)
Keep the ideas coming.
Jim
Jim,
The link I gave you gives you low side psi for ambiant temps.
At 50.51 deg's. your low side will be at 46 lbs psi. And of course, all blended refrigerants have to be inserted in a liquid state to prevent separation.
Nick-
Jim,
Here is another site that explains superheat and also has another charging chart.
Nick-
http://www.mymeterstore.com/crm_uploads/troubleshooting_hvac-r_systems_-_561.pdf
Nick, thanks for helping me with the table from your first link. I never would have gotten that interpretation from the table. It talks about refrigerant temperature rather than ambient temperature. I can't understand why the table below the calculator goes to the extremes if those are truly ambient temperatures.
You mention charging the system with liquid. That would mean inverting the tank. Most of the material I have read suggests that it should be charged by vapor. If you charge with liquid, I assume you still do that on the suction side. (sorry to be such an idiot on this stuff, but I want to understand the process).
I did some more searching and found this site: http://www.wc101.com/guides/refridgeration/page7.htm. Looks like a very straight forward how to do it.
I have found at least two sites that say to check the system for leaks using nitrogen. I carry nitrogen with me to charge extinguishers, so that is easy for me to do.
BTW, I will start over with a new charge, as I think I lost quite a bit with the loose fitting. I will have to wait a bit, as we are supposed to get 10 inches of snow tomorrow :(
Jim
Jim,
Be careful to add the liquid slow... while i have never hurt one "they" tell me that too much liquid to fast can hurt the system -- perhaps someone like Nick can elaborate on the "why"
FWIW
David
Hi Jim & D,
Yes, too much liquid too fast could shatter a hot piston in the compressor. "hydraulic compression"
Jim, all the normal procedures may be out the window anyway since you mentioned a "unique" system..
Start with achieving a target 45 deg. temp at the suction line of the compressor & 55 deg. at the vents, You only want a sweat back not frost.
Outside temps should be around 65-70 deg. just to purge your tank into the system. Your low side gauge should be close to 48lbs
to get you close. If you have a scale, you may determine how many lbs & ounces your system holds for future reference.
At thispoint you can compare your pressures with the charts to see how close you are.
Good Luck
Nick-
Hey Jim
Just remember to have your Condenser Fans turned on when charging.
I will say no more. Ha! Ha!
Catskinner!
Sonnie & Patti Gray
72 0/5 Eagle 3406 Cat
Pottsboro, Texas
OK Sonnie, somehow I knew you would read this and rat on me :o
The story goes that we were in Quartzsite at an Eagle Rally and I thought it was warm enough to top off the system so I could have defrost. When I put the gauges on and added R134, the head pressure went very high. I knew it should not be that high. I panicked and went over to get Sonnie since I know he was good at AC systems. He came over and began scratching his head as well. He asked if the radiator/condenser fans were on and I said sure. Well, I have an air control fan that I can turn off at the driver area. We were in dusty conditions, so I turned them off to keep from flooding the engine compartment with dust. You can guess the rest.
I said that I would not tell anymore more Texas jokes, but now that he has brought it up on MAK board, I can now renege on my promise ;D
Jim
Jim
This may help see-->
http://www.autoclimas.com/Refrigerant%20charge.php
Pete RTS/Daytona