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Old 08-10-2019, 08:29 AM   #21
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Quote:
Originally Posted by CHEESE_WAGON View Post
To simplify a bit more, here are the basics of refrigerant system operation...

Think of the system as not cooling so much, as removing the heat from the intake air charge. The air returned is in actuality having heat removed from it, rather than actually 'cooling' it per se. The refrigerant is in a constant loop of circulation, changing between liquid and gas forms to transfer this heat elsewhere from where it is not desired. You have four basic components in the system...

1) The compressor (the 'heart' of the system, as it were)
2) The condenser core/coil
3) The receiver / drier / orifice tube assembly
4) The evaporator core/coil (where the magic happens)

As the compressor runs, it sucks in low-pressure, gaseous refrigerant, compressing it and creating the high-pressure / liquid side of the system. The old scientific principle of heat expanding and cold contracting is in play here. When the refrigerant leaves the compressor, it takes a liquid form, entering the condenser.

Air blown across the condenser coil cools the liquid as it travels through it. It remains liquid and high-pressure as it enters the receiver/dryer/orifice tube assembly.

The orifice tube filters and meters the flow of refrigerant into the evaporator core, where it expands to return to a lower-pressure, gaseous form, getting super-cold in the process. This is where the system 'sweats', or condensates, forming condensation on the outside of the receiver/dryer and the nearby lines. This is due to the extreme drop in temperature, especially against the higher underhood temperatures around these components.

The air inside the vehicle is drawn across the evaporator, where the refrigerant, now expanded and super-cold, absorbs any heat from the air drawn across the evaporator.

The refrigerant, still in low-pressure, gaseous form, enters the compressor to complete the cycle, where it is compressed, returning to a high-pressure / liquid form before carrying the absorbed heat away to be exhausted through the condenser coil.

And that, boys and girls, is how refrigerant systems work. Some systems have an expansion valve rather than an orifice tube, but the principle of operation is the same, whether it is a car, van, SUV, window-shaker, freezer, or refrigerator. Heat pumps operate pretty much the same way, except they have additional components to essentially reverse refrigerant flow.

Here is a diagram to help to understand the process... You can clearly see how cooling the condenser coil properly is vital to proper and continuous system operation.

Thanks for trying to demystify an A/C system.

A few corrections and suggestions:

Leaving the compressor, the refrigerant is still in the gaseous phase. It is the condensers job - as its name implies - to condense the high pressure refrigerant vapor to the liquid phase. (See here)

You may also want to introduce the concept of latent heat (the amount of energy it takes to facilitate a phase change) in the description of the inner workings of a refrigeration system. Latent heat of the refrigerant is the chief mechanism by which heat gets transferred from the cabin to the outside air. The pressures in the system are merely a way to have the phase changes occur at the temperature ranges existing in the cab and on the outside. (Yes, expanding a gas will drop its temperature and compressing will raise it. But the amount of energy involved there is much less that what is transferred during a phase change.)

Please check out my latest description of the refrigeration process here and let's work together to create, possibly with the help of others, a sticky that is both understandable for the lay(wo)men as well as scientifically correct.
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Old 08-10-2019, 09:26 AM   #22
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Originally Posted by alpine44 View Post
Thanks for trying to demystify an A/C system.

A few corrections and suggestions:

Leaving the compressor, the refrigerant is still in the gaseous phase. It is the condensers job - as its name implies - to condense the high pressure refrigerant vapor to the liquid phase. *SNIP* Please check out my latest description of the refrigeration process here and let's work together to create, possibly with the help of others, a sticky that is both understandable for the lay(wo)men as well as scientifically correct.
*nods* Understand, I am not an HVAC tech by trade, though I do have a little experience in the troubleshooting division of Trane's Building Automation Systems (more or less, control systems for industrial / commercial HVAC systems -- chillers, etc.)... Good job, but was set up to fail from the start with a 'lead' tech that did not want to train someone he saw as his replacement -- it's possible some of his instruction was intentionally misleading, though quite a bit of info on the Internet agrees with what I've outlined here (tried to refresh myself in case memory did not, in fact, serve me). It's also been some time since anything in the line of assisting my old man in his little side jobs and such. He was an electrical contractor by trade, but knew HVAC service as well.

Perhaps minute differences between those I/C systems and the ones discussed here are cross-firing in my head, as that training was in the late 90s. I just try to make it as basic and understandable as possible -- even when it really isn't LOL. However, it's always nice to get input from someone who is perhaps a bit more experienced and can further help.
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Old 08-20-2019, 10:25 AM   #23
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I quickly read through the thread but I did not notice anywhere where Q-Tip stated his location. I know in Canada we can no longer buy R134A as consumers. But it is available online or if you make a quick trip to your closest south of the border walmart or autoparts store. There are alternatives available but they are hydrocarbon based. You're not supposed to mix them and if you do and someone evacuates your system it can cause a real pain when they have to have their machine serviced or go to dispose of the mixed refrigerant tank.
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Old 08-20-2019, 10:49 AM   #24
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Originally Posted by chrisml View Post
I quickly read through the thread but I did not notice anywhere where Q-Tip stated his location. I know in Canada we can no longer buy R134A as consumers. But it is available online or if you make a quick trip to your closest south of the border walmart or autoparts store. There are alternatives available but they are hydrocarbon based. You're not supposed to mix them and if you do and someone evacuates your system it can cause a real pain when they have to have their machine serviced or go to dispose of the mixed refrigerant tank.
Correct me if I'm wrong here, but I believe most charging apparatus units are generally idiot-proof. Factory R134a systems have different style charge ports, so QTip should have no worry there. Even retrofit kits come with replacement valves that thread on to the original R-12 fittings. So while it may not be impossible to to mix refrigerants, I think you kind of have to work at it.
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Old 08-20-2019, 01:29 PM   #25
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if a system had R-22 then R-134A is not as retrofit.. if a system had R-12 then you need to flush and change the oil as R-134A will not pick up and distribute the mineral oil that R-12 used.. and sometimes the oils and refrigerant reacted causing a mess..



you absolutely cannot CHarge 134A and PAG oil into a system as retro fit..



chargine POE oil in over top of mineral oil wont cause reaction but it causes for too much oil (non condensables) in the system. and it wont cool properly...



remember all the people in the 90s who retro-fitted their old R-12 cars and complained about how "my A/C sucks now".. most were related to not doing the conversion correctly... fluish the system, evacuate and recharge with proper amount of POE (I always recommend POE in any retro in cases there were traces of old Mineral oil left).. if a system is brand new then i recommend PAG oil with the 134a..



-Christopher
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