Which is Which: A/C hose

[imageman]

Which hose is which on my 81' 911sc A/C? Which is high pressure and which is low pressure? And can I drain the r-12 and put a conversion kit on and fill it with 134a? Thanks Rob.

[Hugh R]

Do a search on A/C and you'll find lots of info. Specifically do a search on Jim Sims. The hose going to the rear deck lid is the high side. You need to do a lot of more research. You have issues of barrier/non-barrier hoses, the proper oil for 134 vs. R12 they are not compatable and you will seize up your compressor if you don't use the right oil. You need a 134 reciever/drier and an evacuation pump and a set of a/c gauges. If you don't know what you're doing, and you explode the Walmart R-134a can in your hand it can blind you. Homework, Homework.

[rnln]

Hugh R,
You gotta tell me in which case you will (might) explode the walmart can. Remember last year you were helping me on fixing/recharging mine? Now I need to repair/replace one of the hose and will recircle the whole thing again.
Thanks Hugh

[tcar]

Originally Posted by imageman

Which hose is which on my 81' 911sc A/C? Which is high pressure and which is low pressure? And can I drain the r-12 and put a conversion kit on and fill it with 134a? Thanks Rob.

NO. Have a shop remove the R12 - illegal to dump it into the atmosphere.

...and to put R134a into the system, to get enough in, you have to pull a significant vacuum, which they can do.

The compressor lubricating oils (critical) are not compatible w/ each other.

Why do you want to do this? R12 cools better than R134a. (Removes more heat for a given system size).

And... R134a will probably go the way of R12, too. In fact in Europe, it will be restricted after 2011.

[Hester]

Here is my primer on air conditioning. Understanding the basics might help you.

Air conditioning is all about the transfer of heat that happens as liguid evaporates into a gas and a gas condenses into a liquid. As a liquid evaporates into gas, it absorbs heat. As a gas condenses into a liquid, it releases heat. All air conditioning systems utilize theses principles.

There are three main components to the air conditioning system in your 911: (1) the compressor, (2) the evaporator, and (3) the condensor. Other components include the receiver/drier (essentially a filter), an expansion valve, plumbing, refrigerant, and oil that lubricates the compressor.

The cycle starting at the compressor: (1) the compressor takes hot gaseuos refrigerent and compresses it into a hot, high pressure gas. (2) the hot high pressure gas flows out to the condensor which is positioned so as to have contact with outside air rushing across it where it releases heat into the atmosphere and condenses back into a high pressure liquid. (3) the high pressure liquid then flows through the receiver/drier and then to an expansion valve that releases the liquid into the evaporator at the interior of the space being cooled. (4) the liquid refrigerent has a chance to expand again and release pressure in the evaporator where it comes into contact with the warm air in the space being cooled. Because the liquid refrigerant is under less pressure, it evaporates back into a gas and absorbs heat from the air passing over the evaporator. (5) the hot, gaseous, low pressure refrigerant then flows back to the compressor and the cycle starts all over again.

Thus, the high pressure hose is the hose that carries the refrigerant between the compressor and the condensor. The low pressure hose carries the refrigerent between the evaporator and the compressor.

The efficiency of a refrigerant is measured by the temperature and pressure required for it to pass between the liquid and gaseous states. We used R12 until the damage to the earth's ozone layer associated with chlorfluorocarbons (CFCs) caused the federal government to restrict its use. R143A was introduced as a replacement to R12 in the 1990s (see http://en.wikipedia.org/wiki/1%2C1%2C1%2C2-Tetrafluoroethane). I read somewhere that, as a refrigerant, R143a is actually much better than R12.

Unless properly lubricated, a refrigerant compressor may fail prematurely. The lubricant is combined with the refrigerant in the system. Because moisture will damage the compressor and corrode the interior of other system components, it is important that there be as little moisture in the closed system as possible.

The temperature needed to boil water or make it evaporate decreases with atmospheric pressure. When the closed air conditioning system is under a high vacuum, the moisture in the system boils or evaporates at a lower temperature. Thus, the way to get the moisture out of the air conditioning system is to put it under a vacuum. The higher the vaccuum and the higher the ambient temperature applied to the airconditioning system, the more likely it will be that the moisture in the system is eliminated.

I hope this helps. Good luck!

[imageman]

Wow, Thanks everyone. I was going to switch to R134a because I didn't know where to get R12. There is a guy locally that will fill R12. I'll get with him. Thanks a million. Rob

[bmgmd]

Just rebuilt the compressor, had it charged today with R12, no leaks noted, AC guy says hoses look good.

Air at center vent was down to 44F just driving streets for about 15 minutes, not the freeway/highway. Probably lower temps could be reached on the highway.

As long as there are not leaks, I hope to keep the stock system...

[Hugh R]

You want to dump the stuff from the can with the can up, not upside down only into the blue line, that's the low pressure line. Go ahead and shake it but if you introduce a solid slug of liquid you can hydrolock your compresor (the piston is trying to compress a solid liquid) and rupture your compressor. NEVER open the red line with the blue line open, that is what puts the 300 psi of the compressor back into the can, thus rupturing the can in your hand! Wear safety goggle the refrigerant can freeze your eyeballs and blind you permanently. Just remember, the A/C charging block is just a big open space. Meaning that when you open one valve, the other side equalizes.

Originally Posted by rnln

Hugh R,
You gotta tell me in which case you will (might) explode the walmart can. Remember last year you were helping me on fixing/recharging mine? Now I need to repair/replace one of the hose and will recircle the whole thing again.
Thanks Hugh

[rnln]

let's see:
1- the can need to be up side up. Never up side down. Never bottom up. Correct?
2- charge to the lower side valve.
3- "NEVER open the red line with the blue line open". When you say "Open", you mean press on the pin inside the valve, or hook up the charge valve, correct?