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Air Conditioning Charge specs?

Yahoo Message Number: 63069
Does anyone have the pressures and other specs for the OTR A/C for my 42 foot Magna?

Rich 2002 Magna

Re: Air Conditioning Charge specs?

Reply #1 –
Yahoo Message Number: 63071

You don't absolutely need the specs; they are nice to have but not essential. Charge it until the sight glass on the receiver/dryer (it may also be elsewhere) goes from milky to clear and the gauge presssures show cooling is adequate. If you look carefully at the gauge on the scale for the type of refrigerant you are using the numbers next to the pressure value indicate the approximate temnperature of the gas. If the high side shows over ~110 degrees and the cooling/low side ~40 degrees your system will cool very nicely. Some systems are more complicated but it isn't likely at all you will find one in an automotive design like our rigs incorporate.
Any automotive AC shop can do it or do it yourself. You can get a R134a charging line with pressure gauge for about $20 at WalMart and many other places, maybe less. The fitting is a snap on/off so you don't even need hand tools. I do recommend carefully tightening all the line connections you can reach the seals/O-rings can shrink and the fittings loosen as they age.
Last year our stick house system was not cooling, a check of the pressures showed it had lost enoughrefrigerant (don't call it freon) to make the system operate poorly but not shut down for low pressure. I tightened, carefully, the fitings and charged it back in the way I just described and two seasons later it is still working fine. It is a 12 year old system.

Bob (rthandren@...)
'05 Inspire 51178

Re: Air Conditioning Charge specs?

Reply #2 –
Yahoo Message Number: 63085
Rich,

The pressures for all r134a automotive systems are the same. I only check the low side. With your A/C on high and fan on high the target pressure depends upon ambient temperature. Hot day at 90 + you should have low side pressure around 40psi. Cool day at around 70 you should see low side of closer to 30psi.

George in Birmingham
'04 Allure 31038
George in Birmingham
2003 Magna 6298

Re: Air Conditioning Charge specs?

Reply #3 –
Yahoo Message Number: 63131
Thanks George,

This is weird since this tech says it is preferable to have the pressure specs for each vehicle. Says he has them for most cars. I swear I thought someone posted details not long ago here.

Rich

2002 Magna

Re: Air Conditioning Charge specs?

Reply #4 –
Yahoo Message Number: 63133
Rich, that is weird. I suppose that different systems are designed for slightly different evaporator coil temperatures. Different temperatures would require different pressures. So, I guess that would explain why a tech would like to know the unique application specs with precision. I really didn't think of that as I have simply added refrigerant on my own over the last 4 years. I simply looked at the chart found on many r134a cans and used that as a rule of thumb. It worked well for me.

George in Birmingham
'04 Allure 31038
George in Birmingham
2003 Magna 6298

Re: Air Conditioning Charge specs?

Reply #5 –
Yahoo Message Number: 63135

RIch:

George is right, so am I that on at least the professional gauge sets the temperature of the refrigerant is right next to the pressure on the scale. When an HVAC engineer showed me that all the mystery of these systems disappeared.
For the system to function there needs to be a good difference between the ambient temperature and what the high side shows and analgous at the low side/evaporator - cold enough to cool supplied to coach. It ain't rocket science in spite of what shops try to tell you.
The sight gtlass is also there to see when the refrigerant changes phases from gas to liquid which is pretty close to and ideal fill. Setting the system up using these methods may not be "perfect" but in the absence of charts the system will work properly. I've been working/playing with A/C systems for a long time and restore old cars. Ignore the voodoo, use a kit from a store. If the tech doesn't know how to use the sight glass, well, .......
As George also stated, the R134a fill kits sold in the stores include a gauge - just follow the directions. The only real damage you can do is to fill the system so much it locks up. Modern systems are designed with high pressure and low pressure shutoff switches so it is doubtful you could do that.

Bob (rthandren@...)
'05 Inspire 51178

Re: Air Conditioning Charge specs?

Reply #6 –
Yahoo Message Number: 63139
Gentlemen,

It may not be rocket science the way you approach it, but there is definitely more science to it than you give it credit. The reason you get by with alot of what I see written about on this forum is because fortunately these systems are designed to handle extreme conditions. When the conditions aren't so extreme you can get by with some things, but possibly only temporarily. When I read about someone putting in a can or 2 without even knowing what the high side is doing your just shooting in the dark. Maybe you hit your target good enough to make it blow cold, for the time being, but just how efficiently is it working and when the conditions worsen will it continue to cool or even work at all? When your adding your can or two are you even burping the air from the lines? If not, your getting air in the system which will have some level of moisture it, when mixed with refrigerant will turn acidic and will begin to eat away at your system from the inside out while causing it to work less efficiently while it's doing it. Watching the high side is necessary if you want a full understanding of how the system is operating. Without the knowledge of what is happening you run the risk of shelling out your a/c system quickly. (maybe from a restriction in the line, caused by the moisture you just injected into it by not getting the air out of the line before you shot your can in). If you're burping the line you're failing to mention it. This could lead to someone not realizing they need to.
Superheat, subcool and all those A/C wordy functions... who needs them? Maybe the people who would like their A/C to last as long as it was designed to. You can also use regular Antifreeze without SCA's in your radiator. but I don't think you'll like the end run. (I know, There's OAT) When you say to someone in this forum "it's OK to just shot in a can or two" you maybe encouraging someone to destroy their A/C system prematurely. They may not even need any refrigerant! You can't know if you don't put a gauge on the low and the high side and know what the pressures and tempatures are telling you while considering the variable conditions the system is operating in.
I would just hate to see someone shell out or shorten the life of their compressor trying to save a few bucks. Be careful, you can easily save yourself broke! Remember this, "If it's worth doing, it's worth doing right." If you want to save some money, do yourself a favor and at least spend some time and educate yourself on the fundamentals of air-conditioning.
Kevin Burns

00 Affinity #5865

Re: Air Conditioning Charge specs?

Reply #7 –
Yahoo Message Number: 63140
Hi

Get a different tech.

Mikee

Re: Air Conditioning Charge specs?

Reply #8 –
Yahoo Message Number: 63141
Bob,

You cannot use a sight gauge with 134a. When the system is full there will typically still be bubbles in the sight glass. The sight glass was typically on R12 systems.

Mikee

Re: Air Conditioning Charge specs?

Reply #9 –
Yahoo Message Number: 63153
Kevin, most everything you say is true but extreme. Remember that the only reason someone would even think of adding some 134a is because their system is already failing.
Just for perspective I was a trained A/C refer tech but it was nearly 45 years ago and I have not worked in the field since getting out of the service in 1968. But, I remember most of the stuff pretty well.
Speaking for myself, I burp the line of air. It is simple so I do it.
I did it for 4 years keeping a leaking system from costing alot to fix. In my opinion there is so little air in the hose and the function of the receiver/dryer/accumulator so good that a few additions of air will have no/little effect on the system. The notion that this is so risky and complex that an owner shouldn't do it is an example of being overly cautious.
This year, my recharging would no longer work so I had the leak found and fixed for about $250. Both of the hose ends attached at the compressor were leaking. Each was removed, the hose trimmed back to good rubber and new ends were installed. The system was drawn to vacuum and recharged with 4.5 lbs of r134a. It works perfectly so the 4 years of adding refrigerant with low side only pressure did no harm.

George in Birmingham
'04 Allure 31038
George in Birmingham
2003 Magna 6298

Re: Air Conditioning Charge specs?

Reply #10 –
Yahoo Message Number: 63156
Thanks to you all. I am now pretty confused. For the record, this is not a matter of adding refrigerant: The compressor had to be replaced a little over a year ago (due to a belt blowing up). The clutch burned up a few weeks ago for unindentified reasons, so it had to be replaced. This involves evacuating and recharging the entire system, thus the tech's question.

Rich 2002 Magna

Re: Air Conditioning Charge specs?

Reply #11 –
Yahoo Message Number: 63162

Agree with everything you said Kevin but a couple of pints. (I mean points but a couple of pints would go well too.)
Current automotive systems (the type we were exchanging info about) don't use the "super" and other fancy designs. My home unit does and the pressures are somewhat different than straightforward and use of an accurate thermometer and gauge set is definitely needed to get the system to operate correctly.
I believe I also agreed with you that most modern systems (certainly one CC would install in a Magna) include pressure sensors to protect too much or too little pressure but that shouldn't excuse some attempt to know what is in there. In the case of these messages the system was empty I believe having been repaired or serviced. So that is the situation I was attempting to address.
As frequently as automotive systems spring leaks, in large measure because they must operate under the worst conditions most here will encocunter, adding 134a using one of the kits from a store is a valid approach for most of us. Last summer ours acted low and in spite of having more tools and stuff at home than many business I naturally had nothing to add 134a. The cheapest Wal Mart kit had a single hose with a gauge no less. These systems are so simple that if you overfill a bit the low side rises as well and can be seen. The instructions are actually pretty and this little gem of a hose and gauge are in my desk in the RV for the next time. I also use a thermometer to check the output and use in comnbination with everything else available, sight glass and at least low side pressure.
One rule of thumb is if you can observe the sight glass and see the refrigerant has changed from gas to clear liquid with no bubbles it might be a good place to stop. Drive the day and recheck that evening. I don't see how there is much hazard from this. I didn't mean to imply my suggestions are always the right answer but they do work in many cases from personal experience.
I also usually mention several times that carefully tightening all the connections you can get at will frequently take care of the leak. This should be done the right way using two wrenches so as to not twist that weak aluminum tubing.
So, if one has access to the correct instructions, tables, gauges and equipment absouletly do it the "right" way. But if one or more are missing and you want to get back on the road with at least some cooling it can be done.

Bob (rthandren@...)
'05 Inspire 51178

Re: Air Conditioning Charge specs?

Reply #12 –
Yahoo Message Number: 63163

Mikee,

Thanks for the info - you work on them daily so I know you are right. I appreciate it.
The aftermarket system on my street machine has a sight glass - it is only 2 years old so I doubt it was leftover R12 stuff, the hoses were made from scratch. I have been unable to find a sight glass on the Inspire so just assumed it was in an inconvenient place and as described in another post I tightened what I could and added 134a using a Wal Mart low side hose with builtin gauge. It worked. System is still working even in this lousy FL heat and humidity. No sight glass and the fact it doesn't necessarily reflect the phase shift of the refrigerant may be why WM (or the mfr) installs a lowside gauge.

Thanks for updating my knowledge.

Bob (rthandren@...)
'05 Inspire 51178

Re: Air Conditioning Charge specs?

Reply #13 –
Yahoo Message Number: 63165

George,

You actually fessed up to burping the AC line! Good for you, done it quite a few times and never had a problem - yet. I didn't have the guts to confess figuring that would really my comments overboard for the purists. I have nothing aganist purists, I am a purist in may ways myself including appreciating the purity of my money and ways to avoid giving it to someone else when not otherwise necessary.

:-)

Bob (rthandren@...)
'05 Inspire 51178

Re: Air Conditioning Charge specs?

Reply #14 –
Yahoo Message Number: 63166
So, can anyone shed any light on how to "burb" the system?

Larry, 03 Allure, 30856

Re: Air Conditioning Charge specs?

Reply #15 –
Yahoo Message Number: 63167

As was recommended by Mikee, get another tech. This should not be totally stumping this fellow.
Starting from scratch is actually better. Did you check the old compressor and look around the coach for a tag/label that states how many pounds of refrigerant were used? There should be one someplace, check the front and rear portions of the system. If you find it add the refrigerant indicated except for the last pound or so. (The tech should have looked - ask him/her where this tag/label is.)
From there on everything else we described still applies as you are adding refrigerant.
In the absence of a label a totally SWAG on my part would be to start with 3 lbs, watch the gauges and stick a thermometer in a dash register to see what is happening.

OK, I went into the garage and dug out my R143a gauge set.
On the high side gauge a pressure of 150psi equates to a temperature of about 115 degrees.
On the low side gauge a pressuer of 35psi equates to about 40 degrees.
The high side is the "outside" of the system and it needs to lose heat and send it back to the cab of your rig. If the outside temperature is 100 degree a pressure at 150psi indicates 115 degree this leaves about 15 degrees difference. This means the condensor should be able to lose heat to the ambient outside temperature - it is hotter than the outside air.
The low side is the "inside" of the system and needs to remove heat from the air so the cab will cool down. 35psi = 40 degrees. This is cold but not cold enough to cause the evaporator to freeze up from the condensation of water - the same as a glass of ice water gets wet condensing the water in the air. The cab should be successfuly cooling.
The warmer refrigerant used to cool the cab is now sent back outside where it is compressed by your new compressor and then sent to the condenser near your radiator outside to lose the heat it collected inside. The pressures the system generates when charged properly are how it accomplishes this. I hope this makes sense to you - it is all about heat transfer inside and outside.
These numbers I used are not caste in concrete! Each AC system has a capacity and if, for instnace, it is too small the pressures will not be right to accomplish the needed heat transfer. If your system cannot achieve this level of performance there may be another problem that needs to be fixed. For example a bad expansion valve will not allow the evaporator to work properly, get cold and absorb heat.
If your tech doesn't understand this you are using the wrong shop. Like I others have said - it ain;t rocket science for these systems.

Bob (rthandren@...)

'05 Inspire 51178

Re: Air Conditioning Charge specs?

Reply #16 –
Yahoo Message Number: 63169

Larry:

Just keep the burping to a socially acceptable level please. Decorum on this board ia appreciated.
If you are a DIY type and you don't have a megabuck install and recovery system (a legal requirement for professional shops - one reason this work can be so expensive.) you can flush the system using some refrigerant. You disconnect a fitting at the opposite end of the system from where the input valve. Then I simply, verrrry sloooowly bleed (burp) a portion or even a whole can of redrigerant (e.g. 134a our systems use) through the system. The only time I use a whole 1lb can is when the system is new or been repaired and is completely full of air.
The correct way is use a vacuum pump to draw down and test the system and although R134a isn't supposed to be environmentally hazardous, businesses are not allowed to vent to the atmosphere. The vacuum pump also allows you to check for leaks - it either holds a vacuum or lets air back in. The air might contain water which could freeze and compromise the operation of the system.
As George pointed out, the receiver/dryer is usually the size of a supersize can of beer. There is enough silica gell in there soak up a lot of water. Burping the system pushes the air out; any small amount of air/water left will be picked up by the silica gel.

And it's a silent burp, no one will know but you.

Bob (rthandren@...)
'05 Inspire 51178

Re: Air Conditioning Charge specs?

Reply #17 –
Yahoo Message Number: 63170
Thanks Bob. There is no label but I have the A/C charge sheet from CC. It says that a 42 ft Magna taks 6 lbs. 134. Then it says this:

"Note: Starting at the low side of specified charge will Ensure that you will not over charge the system. Also Capacities may vary depending on the length of the coach.
Once charged you will need to run the system and take a Temperature reading at the input and output sides of the System and must be an 18-20 degree differential (Delta T) 20 degrees is optimum for customer satisfaction. Once Tested if you are not able to maintain the specified Temp Range you can then continue to increase the charge in .5 lbs Increments until system is within range and properly Cooling."
One of the techs said that overcharging the system is entirely possible and this could eventually result in clutch failure.
I am having a nightmare since the shop that installed the latest compressor has this big fancy A/C charge machine. They said that their machine clogged up probably due to "stop leak" in my system and they had to do it the "old fashioned way" with a scale and guages and all new R134. This "stop leak" thing is very strange since I have had since two fittings on the condensor were replaced a few years ago by Rocky Mountain Cummins in ABQ and to my knowledge. They recharged it, it worked perfectly and to my knowledge no one put any stop leak in. Twice since then the system was recharged (new compressor and then adding more since the new compressor was not cooling as well). Neither of these shops had a problem with stop leak in my system or their machine.

Rich 2002 Magna

Re: Air Conditioning Charge specs?

Reply #18 –
Yahoo Message Number: 63171
Sure Larry. You don't burp the system you purge the air from the refrigerant air hose. When using the simple single hose and gauge that has been mentioned it is simple. This is done to prevent polluting the refrigerant with air and moisture.
First install the refrigerant can onto the hose. Turn the puncture device to pierce the can. You will see the pressure reflected on the gauge. At the other end of the hose is a quick connect fitting that will mate with the low side access port. Inside this fitting is a spring and pressure valve. Using a device like a screw driver or a pencil probe inside the fitting and release a small burst of combined refrigerant and air under pressure. Your hose is now filled with more or less pure refrigerant.
Now shut of the valve prevent the cans pressure from entering the hose. Connect the hose to the low side access port and slowly open the valve releasing refrigerant into the system. Continuously agitate the can and rotate it from vertical to about 90 degrees until the can is almost empty. When almost empty turn is upside down to ensure that all the product is injected to the system. This takes some time. Also, watch the pressure gauge to ensure that you do not exceed about 40 lbs on a hot day or 30 pounds on a cooler day. You do not want to speed up the process by holding the can upside as this will inject liquid refrigerant which can destroy the compressor. All of these instructions(except the burping) are on the can.
I know it's ideal to use a full set of gauges and in the hands of a qualified technician. But, you would have to violate at least one of the instructions above to be at all likely to do damage.
This will not work on a system that has no pressure and has been fully or nearly drain of refrigerant as air has likely already compromised the system.

Good luck should you choose to DIY.

George in Birmingham
'04 Allure 31038
George in Birmingham
2003 Magna 6298

Re: Air Conditioning Charge specs?

Reply #19 –
Yahoo Message Number: 63172
On the subject of Temperature Delta between input air and output air. There are variable here as well. The primary variable are compressor RPM, humidity and fan air speed over the evaporator and the condenser.
I can tell you that if all you can achieve is a 20 degree delta on a low humidity day as you drive down the highway you are not going to be happy with the performance. A properly running A/C is going to flow about 40 degree output air when the conditions are dry, input air is around 80, the evaporator fan is on medium or low and the hydraulic fan controller is working properly. Change any of the variables and performance changes. For example, when my fan controller failed and the cooling fan was on high all the time my A/C ran ice cold. This was because the condenser had constant cooling leading to increased heat removal.

George in Birmingham
'04 Allure 31038
George in Birmingham
2003 Magna 6298

Re: Air Conditioning Charge specs?

Reply #20 –
Yahoo Message Number: 63175
I for one understand, in my Prevost, CC OTR air is I think 12 #. Its 40'and R12, so at 60 bucks a pound I would not take any chances of overfilling plus the problems that can cause.

Re: Air Conditioning Charge specs?

Reply #21 –
Yahoo Message Number: 63179
Hi

"Pulling a vacuum" on the system is used for leak check, but its main purpose is to remove water. At 29 inches of vacuum water will boil at 70 degrees F. The vacuum causes the water to turn into steam and be removed. A vacuum pump cannot remove liquid water, it will just lay where it is short of a high pressure flush. I have made a fair amount of beer money betting folks I can boil water at 70 degrees, a lot of it from AC techs... There is a huge misunderstanding of the real purpose of the vacuum pump.

Mikee

Re: Air Conditioning Charge specs?

Reply #22 –
Yahoo Message Number: 63180
Thanks Bob! That clarifies it for me. I don't have an issue yet, just curious for future reference. And yes, I should have excused myself :)

Larry, 03 Allure, 30856

Re: Air Conditioning Charge specs?

Reply #23 –
Yahoo Message Number: 63184

Makes good sense. I like your procedure. I did have a leak on my SOB that only showed up under pressure. It did not leak under vacuum. We found it by pressurizing with nitrogen and using soap bubbles.

Dave

aka Billy Byte (trusty hound)
2000 Allure #30443

Re: Air Conditioning Charge specs?

Reply #24 –
Yahoo Message Number: 63185

Kevin

I have a case in point for you. This is why I took a class in A/C. My air quit in my 'other' coach and I had a residential A/C guy look at it. He charged the system from the low side w/o looking at the high side. After adding a significant amount of R-12 with out any cooling he put his gauge on the high side. AND promptly blew his high side gauge. The valve on the evaporator was plugged due to the filter dryer puking into the system. Needless to say I had to replace the entire high side hose from the compressor in the rear to the condenser in the front of the coach. Luckily, nothing else failed.

Dave

aka Billy Byte (trusty hound)
2000 Allure #30443