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Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

We're back for 2014 2015 2016 2017 2018, sweaty goons.



AC repair is something that shouldn't be attempted unless you are willing to learn how to do it properly. Incorrect repairs and maintenance very often end up costing far more to repair later than you've saved by attempting to bodge it up yourself. No matter what the "recharge kits" you find at the parts store say on them, no.....it's not that easy. If you are lucky it just might work, but it's still the wrong way to go and presents unneeded risks ranging from simply wasting money to bodily injury.



Still with me? OK, then this is the thread for you. Because we're gonna do this the right way with fairly inexpensive tools you can buy or borrow from a parts store, rather than with a $7500+ machine like they do at an actual shop.

I'm going to break this down into a few posts to cover various topics/scenarios. It's all going to be really general, so don't sperge at me about your exceptions. There are always exceptions, and anyone who's been alive for more than 5 years has already figured that out.



For now, let's start by covering some basic terminology:

Refrigerant - This is what's in your AC system that makes it cold. No, it's not Freon (probably). Just call it refrigerant unless you know what it specifically is.

R-12: This is a great refrigerant but was phased out of new vehicle production in the '90s because it's not so good for the atmosphere. It is still available as new old stock or recycled, but it is illegal to produce any new R-12. You need an EPA 609 certification to service an R-12 system or buy quantities of less than 30 lbs. Fortunately, it's an open book online test that only costs $30 or so. http://epatest.com/

Freon - The DuPont registered trade name for R-12

R134a - This is probably what you have in your car. Only recently have some other alternatives come to market in a vehicle from the factory.

Condenser - This is the radiator-looking thing that's likely to be in front of your engine's radiator.



Evaporator - This also looks like a small radiator and is nearly always buried somewhere completely goddamn inaccessible. It has to be in the stream of air going through your cabin comfort air system, so it usually ends up in a box under the dash along with the heater core. If you're lucky it might be accessible under the hood.



Compressor - One of those things your serpentine belt turns in front of your motor. Most have a magnetic clutch so that when it's not on the pulley around the outside can still spin but the compressor itself doesn't move. Newer models have internal mechanisms to vary their displacement for greater efficiency.



Dryer (receiver/dryer) or accumulator - These are different things for different types of systems, but the important part is that you'll be replacing them any time you've opened the system to the atmosphere. They have a one-shot-use desiccant pack in them to get any remaining water out of the system after it's been opened. Water turns refrigerant acidic which will eat the system from the inside out.



Expansion valve or TXV - This is a venturi and/or nozzle that liquid refrigerant flows through to be atomized on it's way into the evaporator. This is where the physics come in. If you rapidly decompress pretty much anything it will get cold. Find something that is particularly good at getting cold when it changes phases like that and we call it a refrigerant. This works with all kinds of stuff including ammonia and propane. In fact, both of those are still in service today as refrigerants.



Capillary tube - Like a TXV but for a different type of system. The type that would have an accumulator. These systems are cheap and lovely and what you are likely to find in your car unless you spent some bucks on it.

Most importantly: THIS poo poo CAN BE DANGEROUS



DO NOT start poking around or unbolting things unless you are positive you understand what you are doing. Refrigerant is under pressures up to 400 PSI in vehicle applications and can be even higher during specific types of failures. Venting this refrigerant into your face or hands WILL BURN YOU. As in, instant frost bite, flesh turning black in hours kinda poo poo. Don't be stupid. Know what you are doing, wear safety glasses, long sleeves, and gloves among other appropriate protective equipment.

Motronic fucked around with this message at Mar 21, 2018 around 22:27

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Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

THE REFRIGERATION CYCLE

This is to move you from "high speed parts swapper" status to someone who can actually diagnose things. This starts with understanding the very high level basics of how refrigeration works. AC is plumbing for geeks. It's really awesome technology. You don't have to like it as much as I do, it's OK.



It's difficult to describe because it's a cycle. You need to understand all of it to understand any of it. You also need to understand that this type of refrigeration requires a phase change from liquid to gas and what is in your system is specifically chosen to be on the edge of that phase change during normal operating conditions.

I'm going to just pick a spot and start from there. Let's say......compressor.

The compressor fills with somewhat warm low pressure refrigerant and oil in a gas form. It does what compressors do and pumps that poo poo up in pressure. In the process of this compression it gets hot.

A side note here...I did say refrigerant AND oil. There is oil in the system that is specifically chosen to mix with the refrigerant in your system. It is critical to have enough but not too much. It circulates along with the refrigerant as part of the cycle.

The high pressure side of the compressor sends this hot gaseous refrigerant to the condenser. Where it condenses. Surprise. It does this because the condenser drops the temperature just like what any radiator is designed to do. Most condensers have an electric fan in front of them that will run whenever the AC is on. It may even be one of your normal electric engine fans. This is done for when you are stationary or driving slowly. It needs airflow or it's just not going to phase change.

Next up, the receiver/dryer. As mentioned in the previous post, this has a desiccant in it that removes water from the refrigerant. If the system has been on for more than a few hours that process is all over now and you either have some desiccant left that can still soak up some water or you did a lovely job of vacuuming (to be described later) and it's all used up and there is still water going past it. Either way, that desiccant no longer matters at this point and the receiver/dryer is doing almost nothing. It stays in the loop and just passes liquid refrigerant through it, although it does act as a bit of a buffer/reservoir.

After the receiver/dryer we're on to the input side of the expansion valve. The refrigerant goes through a venturi that allows the somewhat cooled off liquid to rapidly phase change into a cool gas. There's the magic. Now what the hell do you do with that cool gas?

You shove it through the evaporator. It's just another radiator, this one under your dash just like the heater core. The cabin fan blows through it which cools the air by warming the evaporator.

Now we go to the output side of the TXV (expansion valve). The temperature of the gas coming out of the evaporator changes the position of the TXV, allowing more or less refrigerant to flow through it. This is a carefully calibrated process that keeps the evaporator from getting too cold. If that happens the evaperator freezes and your AC stops working (ice is a lovely heat conductor). How fast that would happen if things go unchecked depends on how humid it is outside/inside. Systems with accumulators and capillary tubes (not receiver dryers and expansion valves) can't do this and suck. But they sure are cheaper to make. They rely heavily on a narrow window of refrigerant fill to make up for their lack of management...go below that narrow window and performance suffers. I'll cover those differences later.

Oh yeah....the byproduct of this cooling is water from the air in the cabin. That collects in a tray at the bottom of the airbox and flows out of the condensate drain(s) under your car. That's why you leave wet spots when you idle with the AC on.

So...now we have warm refrigerant gas. It's done it's job and can't cool any further......so we go back to the compressor to complete the cycle.

Motronic fucked around with this message at Mar 21, 2018 around 22:28

Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

BASIC RECHARGE

First we need to figure out if your shitbox a candidate for recharging. If the AC is kinda working but not very cold and you can hear the compressor clicking on and off a lot it probably is. This is assuming that everything else is working like your cabin fan. The other criteria here is that you don't actually have a leak. So if it's not more than 5 years old or has been charged in the last 5 years you really shouldn't be charging it: you should be finding the leak and fixing it first. The rubber hoses in the system are called "barrier hoses". Neither them nor the seals between components are completely refrigerant tight, so it is normal to lose refrigerant over the years. Most vehicles I've dealt with that are in proper working order haven't lost enough refrigerant to cause any cooling related issues until pretty close to 10 years on the road. Some are worse than others, like things with rear air conditioning (more barrier hose).

Now to verify all is well and you are just low on refrigerant. You need to know what's in there. It's going to be R-12 or R-134a. Then you need to get a manifold gauge set appropriate for that refrigerant. If it's R-134a you're in luck.



Now you need to find the high and low side fittings. These are usually somewhere obvious and often close together, but that's not always the case. R134a fittings look like quick disconnects when the cap it off. R-12 fittings look like a big tire valve when the cap it off. In either case the caps simply unscrew (the inside of the 134a fittings are threaded for the cap - this thread is not used for service). You should make sure they have good seals in them, are clean, and replace them when you are done.



Now make sure the car is off and the valves on each side of the manifold gauge set are CLOSED. Put your drat leather gloves on. And eye protection. Seriously. Hook up the blue line (with a black stripe if it's a proper R-134a set) to the low port. It won't fit on the high side. Then connect the red line to the high side. The just push down and click in place. You shouldn't be able to pull them back off unless you pull up on the collar of the fitting at the end of your gauge set hose.

If you are doing this on an R-12 you'll need to do the same thing, but you have the screw the fittings on and you CAN screw up high and low (well, I suppose you can do this with R134a as well by jamming the high on the low port - it will spit some refrigerant at you). High is typically going to be by the receiver dryer, and low....somewhere. Sometimes even right off of the compressor. Here's where Porsche put them on the 944s for exactly a year and a half (85.5 and 86). After that the low side went to the compressor which is accessed from underneath and requires a 90 degree fitting:



Now that you're hooked up with the car off you have the pressure on the high and low sides of the system flowing up the hoses past the gauges and to the closed valves. This means there is no reason to mess with the valves at this point to get a reading: you are already direct to the gauges. If all is well you should see some sort of pressure. This is called the static pressure.

So what should it be? That depends on how warm it is outside.

Let's say is 90 degrees, so we assume your car and the refrigerant is also 90 degrees:



It's right on the gauge. Look at the R134a temperature line and see what the equates to in pressure. It's that simple.

Now there are three things that you may find:

- It's lower than that pressure: This means you have only gas phase refrigerant in the system, meaning there is almost nothing in there.
- It's at the correct pressure: You have some amount of liquid refrigerant in the system. It could be a thimbleful, it could be a tanker truck full. That's just how physics works. No matter how much or how little of a liquid you have it's vapor pressure is constant at a given temperature.
- It's too high: that's bad. You have contamination in the system. Just stop here, you're not recharging it. You have repairs to do.

One other possibility is that you may have one gauge different that the other. If the car hasn't been off/AC off for at least an hour I wouldn't sweat this one, but I would wait it out and try again to be sure. If it's been off overnight and you have different pressures you likely have an obstruction in the system and not only shouldn't you be charging it, you shouldn't be using it at all until you repair it.

So let's assume this has all worked out: you have a low or correct pressure reading on both the high and low side, plus the other criteria previously discussed. This makes it look like an even better chance you can get away with just charging it. On to running pressures. Make sure the hoses aren't going to get tangled up in any moving parts. Make sure you haven't left tools and poo poo in the engine bay. Start the car. AC on full blast, recirculate if you have it (or "MAX AC" on more Fords), windows up and all that. Close the thing up and let it run. We want to let the AC draw as much moisture as possible from the cabin so the evaporator doesn't freeze while we're charging.

Now go back to the gauges. What you should be seeing is the low side going down in pressure as the high side goes up. Then you'll hear your compressor click off and both gauges will swing back to near the static reading. Then it will click back on an repeat this cycle. That's called short cycling.



If your static reading was below 60 or 70, this may not even happen as the "low pressure cut off" switch will probably never even turn on the compressor.

Either way, it's time to put in a bit of refrigerant and see what happens.

Get a can of R-134a. No leak stopper poo poo, just pure R-134a. Get at least one can with dye in it if you see it on the shelf. They don't all need dye. You also need an R-134a "can tap"/refrigerant valve. They're cheap.



When it is screwed all the way in, it will be closed, BUT it has a pin sticking down that is used to break the seal on the can, so you need to OPEN the valve almost all of the way. You do NOT want this pin getting anywhere close to that can seal right now.

Connect your refrigerant valve to the service line (yellow hose) of your manifold gauge set.

Screw the can of refrigerant onto the valve. At this point, the valve you are screwing the can on should be open, and both valves on your manifold gauges should still be closed.

Once everything is all set, CLOSE the valve you put on the can. All the way. You will feel some resistance, and you will hear it hiss. Once itís been closed all the way, the seal is all the way punctured, and you can re-open that valve all the way.

Side note for R-12. They have no threading on the cans. So you get you bust a hole in the side with one of this style can tap:



Some have valves, some don't. Mine doesn't but an R134a valve fits on it so that's what I use. In this scenario you hook that whole contraption up to the service line, put your $35 can of ozone-annihilator in the jaws of the tap and crank it closed swiftly and firmly so the can is punctured and sealed without losing any.

Now back to the generic instructions.

At this point, your service line is charged from the can, your high and low lines are charged from your system, and the only thing between the two are the valves on your manifold gauge.

Now SLOWLY open the low side manifold gauge valve. Youíll see the pressure shoot up to 80 something, the compressor will kick on, it will get dragged back down, it will happen again, etc. Let it go SLOWLY (valve barely open) for 30 seconds or so. Now close the valve. CAN UP THE WHOLE TIME. NEVER INVERTED OR ON IT'S SIDE. Yes, there are times when that is appropriate, but for a basic recharge it's not. If you invert the can you are going to dump liquid refrigerant into the lines and into the low side of the compressor (remember that second post? It's not supposed to be liquid there!). Liquids don't compress. This makes bad things happen. It's called slugging the compressor. If you slug it real good, especially if it's a Sanden, you'll have some pictures for the Horrible Mechanical Failures thread.

What do you hear? Probably still a compressor that is short cycling (or finally doing something), but itís cycling longer now. Open up the low side valve a little bit again. Let in some more. Slowly. I like to stop every 20 or 30 seconds and just let it go for 30 seconds or so at this point in the process. If you donít, you might freeze your evaporator.

If you started with no compressor engagement and the low side is 80-90 (might need to shake the can) and it still won't turn on, just stop. You have a repair issue.

So if all is going well so far, keep adding. Here's a chart to give you a basic idea of what you are shooting for:



Eventually the compressor will stop short cycling. But keep going until you get the required pressures but not over. Too little is always better than too much.

Some things that will be going on here: the can is gonna get cold. The head pressure of the refrigerant will drop because of this, so it will exit the can slower. Also, you may freeze your evaporator if the humidity is high, especially with accumulator systems. If that happens the compressor is just going to shut down due to low pressure on the low side. No big deal, just shut everything down and wait for it to thaw out. To avoid that, slow down and make sure everything is closed up in the car. Once you have a sufficient charge it won't happen.

You might even need more than one can. If you do, just close the manifold gauge, close the refrigerant valve, remove the refrigerant can and valve from the service hose, CAREFULLY open the refrigerant valve to release the residual pressure, and follow the original procedure for attaching a can of refrigerant.

Leather gloves and eye protection for all of this.

Motronic fucked around with this message at Mar 21, 2018 around 22:30

Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

Reserved

Yu-Gi-Ho!
May 12, 2006

STOP THE PIG
PUT A BULLET IN ITS HEAD




Yay!

Okay... so as seen in stupid questions. Is there any way to safely get away with replacing everything except the evaporator, assuming the evaporator is backflushed properly, and an inline filter is installed? The warranty at the compressor I'm looking at claims to require proof that the evaporator has been flushed and everything else replaced to be valid (2 brands require this, one is fairly well known, the other isn't quite as well known).

I know the evap is cheap overall, but it's also the thing that the entire loving car is built around, and would add about a day to a day and a half of labor. I don't plan to keep the car for more than another year, and every shop I've talked to tells me to just flush the poo poo out of it and throw in an inline filter.

I currently have an expansion valve, condenser (which includes receiver/dryer), new (not reman) compressor, and all (OEM) underhood lines in my shopping cart at Rockauto. I know the lines could be flushed, but the schraders are seized in their bores (they open fine, but can't be removed), so I may as well do them at the same time - the complete lineset only adds $100.

I probably won't do the flush myself, since I don't have access to shop air. Everything else will be me.

Probably do a 152a conversion too, since lower pressures = better mpg, in theory.

Yu-Gi-Ho! fucked around with this message at Mar 22, 2018 around 06:19

Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

Is the evap parallel flow? If it is, there is no way to actually flush it. And it probably is.

IOwnCalculus
Apr 2, 2003





Welp. 2013 CR-V, has had awesome air conditioning from new until today. Started short cycling and blowing warmish air.

Downside is there's basically no DIY info specific to this model out there because they just aren't breaking yet, and I'm a cheap bastard who hates paying Honda $10 for one-day access to the factory service manual. There's not even an option to just buy the drat thing.

Upside, if I do have to open the system, looks like Honda was nice enough to make the dryer serviceable.

Cocoa Crispies
Jul 20, 2001

Vehicular Manslaughter!



Pillbug

IOwnCalculus posted:

Downside is there's basically no DIY info specific to this model out there because they just aren't breaking yetÖ

What's the bathtub curve like on car A/C systems anyways? I've had my ride for just about six years now, and I use the A/C most of the year. Should I expect it to go bad yet?

Terrible Robot
Jul 2, 2010

EUPHORIA IS BEST EXPERIENCED MOST FIRMLY AT THE STATE OF A GRAND CRUSADE AT 10000 DEAD HERETICS AND YOU DON'T KNOW WHETHER YOU'RE GONNA END UP WEARING THESE STUPID FUCKING PAULDRONS OR NOT



Slippery Tilde

IOwnCalculus posted:

Welp. 2013 CR-V, has had awesome air conditioning from new until today. Started short cycling and blowing warmish air.

Downside is there's basically no DIY info specific to this model out there because they just aren't breaking yet, and I'm a cheap bastard who hates paying Honda $10 for one-day access to the factory service manual. There's not even an option to just buy the drat thing.

Upside, if I do have to open the system, looks like Honda was nice enough to make the dryer serviceable.

pay for the access, spend all day taking screenshots and saving them to a folder?

Applebees Appetizer
Jan 23, 2006

It's gone awful quiet in here



2012 Scion xB. A/C blows cold once it gets going, the problem is it doesn't get going for a good five minutes once the car is started and blows hot air until then. That's usually after it's been sitting, if I get out of the car and back in in a short amount of time it still blows cold tho. Sits overnight and it's back to a delay.

Any ideas what's causing it?

IOwnCalculus
Apr 2, 2003





Terrible Robot posted:

pay for the access, spend all day taking screenshots and saving them to a folder?

Pretty much what I did last night, yeah. At least they make it easy to print to PDF.

DJ Commie
Feb 29, 2004

Stupid drivers always breaking car, Gronk fix car...


Applebees Appetizer posted:

2012 Scion xB. A/C blows cold once it gets going, the problem is it doesn't get going for a good five minutes once the car is started and blows hot air until then. That's usually after it's been sitting, if I get out of the car and back in in a short amount of time it still blows cold tho. Sits overnight and it's back to a delay.

Any ideas what's causing it?

My guess is the condenser fan isn't operating reliably. Could be the TXV isn't opening/closing correctly, low refigerant, contamination, etc.

Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

Applebees Appetizer posted:

2012 Scion xB. A/C blows cold once it gets going, the problem is it doesn't get going for a good five minutes once the car is started and blows hot air until then. That's usually after it's been sitting, if I get out of the car and back in in a short amount of time it still blows cold tho. Sits overnight and it's back to a delay.

Any ideas what's causing it?

Check the refrigerant charge. Sounds a lot like low refrigerant leading to the evap freezing.

Applebees Appetizer
Jan 23, 2006

It's gone awful quiet in here



I have checked with one of the cheapo gauges and its in the green.

Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

Applebees Appetizer posted:

I have checked with one of the cheapo gauges and its in the green.

Is there a (clogged) cabin air filter? Or can you pull the blower to make sure it's not packed full of poo poo?

Low air flow will cause the same problems.

Applebees Appetizer
Jan 23, 2006

It's gone awful quiet in here



Just recently changed the filter, and I think the blower should be fine considering the car is only six years old but I'll take a look if I can.

IOwnCalculus
Apr 2, 2003





IOwnCalculus posted:

Pretty much what I did last night, yeah. At least they make it easy to print to PDF.

It's already proved useful, at least. I thought it was short cycling, though my wife didn't seem to know what I was on about. Turns out the Honda system will still run without enough refrigerant in it to fill the evaporator. It will still have enough to cool the passenger side, but not the driver's side, resulting in a significant difference between the two.

Now to see if I can find a reason for refrigerant loss in five years, though it's such a small full charge (less than a pound) that I think any loss would be bad.

Motronic
Nov 6, 2009

MOTRONIC FOR MODERATOR, MAKE AI GREAT AGAIN


Grimey Drawer

Applebees Appetizer posted:

Just recently changed the filter, and I think the blower should be fine considering the car is only six years old but I'll take a look if I can.

FYI, I've found blower fans packed full of poo poo (well, mostly not actual poo poo, I mean scraps of paper/foam/fabric) from rodents with NO other apparent rodent damage, as well as plastic bags and poo poo that somehow weren't making any noise.

A lot of time blowers are a bitch to get out, and if yours is I'd suggest grabbing a cheap endoscope camera thing off of amazon or ebay that you can plug into your phone or a laptop so you can snake it on through there rather than tearing your dash apart.

Applebees Appetizer
Jan 23, 2006

It's gone awful quiet in here



The blower is right under the filter so it's easy to inspect, and it's fine. Filter was fine too.

However as an experiment I ran the ac without the filter and it did much better, but i need to try after the car has been sitting overnight to see what it does that will be the definitive test. Is it possible the aftermarket filter is too restrictive? Maybe I need an OEM filter?

joat mon
Oct 15, 2009

I am the master of my lamp;
I am the captain of my tub.


Not having any problems and my questions have already been answered, but I really appreciate each iteration of this thread.

Adiabatic
Nov 18, 2007



joat mon posted:

Not having any problems and my questions have already been answered, but I really appreciate each iteration of this thread.

Applebees Appetizer
Jan 23, 2006

It's gone awful quiet in here



Applebees Appetizer posted:

However as an experiment I ran the ac without the filter and it did much better, but i need to try after the car has been sitting overnight to see what it does that will be the definitive test. Is it possible the aftermarket filter is too restrictive? Maybe I need an OEM filter?

This was short lived, btw. The next afternoon after it had been sitting had the same result. Gonna take it in here soon to the local a/c guy to see what's going on, hopefully it's not too expensive

Dave Inc.
Nov 26, 2007
Let's have a drink!

I had to replace my A/C condenser after I cracked it and puked refrigerant everywhere. I did that, but I still have the old air drier in the system. I'm a few weeks out from getting it recharged, should I replace the drier now and let it sit in the system or have it replaced right before the recharge? Would it even make a difference?

Enourmo
May 20, 2009

I CAN'T BELIEVE THEY SMOKE THE DEVIL'S LETTUCE IN COLLEGE!!!


If you replace it right now and get it vacuumed, it should be just as good as doing it right before the vac/fill. Both methods only allow it to absurd moisture for a brief period before it's removed.

Replacing it and leaving ambient pressure air in the lines lets it soak up all the humidity, potentially saturating it and leaving it unable to absorb whatever residual moisture is left after you vacuum it later.

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Dave Inc.
Nov 26, 2007
Let's have a drink!

Kind of what I figured, thanks. I don't have a vacuum so I'll leave it out for now.

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