Automotive AC primer: Basic Recharge

In the “SomethingAwful is self destructing series…….

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 damn 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 shit 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 shit, 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 it’s 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. You’ll 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 it’s 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 don’t, 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.

Automotive AC Primer: The Basics

Because the SomethingAwful forums are ready to explode, I’m going to move one of my threads over here. At least the first posts.

We’re back for 2014 2015 2016 2017 2018 2019 2020, 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 sperg at me about your exceptions.

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 shitty and what you are likely to find in your car unless you spent some bucks on it.

Most importantly: THIS SHIT 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 shit. Don’t be stupid. Know what you are doing, wear safety glasses, long sleeves, and gloves among other appropriate protective equipment.

How (not) to use DTCs (check engine codes) to diagnose problems

I see a lot of misunderstanding of what it means when your “check engine light” (MIL: Malfunction indicator Lamp) is on and what the “codes” (DTC: Diagnostic Trouble Codes) mean. Let’s discuss this a bit in general terms that apply to most vehicles and situations. As with everything, there are always exceptions.

First of all, why does your MIL come on? It’s because the ECU has stored a “hard” DTC. This is an event which likely has happened many times and with sufficient severity that the DTC has gone from a “pending” state (which you can read with a code reader but does not illuminate the MIL) to a “hard” state.

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944 Parts Cross Reference

I recently tried to find this information with a bookmark I had set.  Apparently this site no longer exists, so I rescued the information from archive.org and figured I’d post it here.  This used to live at: http://members.cox.net/dnwong/porscheref.htm.

The following are a list of Porsche Parts and their common cross references.

CAR

PART

CROSS REFERENCE / PART #

DISCUSSION / THREAD / NOTES

NOTES

944/951 Ref and Speed Sensors BMW
12 14 1 708 618
12 14 1 710 668
http://forums.rennlist.com/rennforums/showthread.php?t=167724

944/951

Visor Clips VW
3B0 857 561 BY20 . . . $4.68 . . . Pearl grey
3B0 857 561 BB41 . . . $5.01 . . . Black
3B0 857 561 B8YS . . . ($.?.) . . . Light Beige

For the clip-on dress cover:

3B0 857 563 BY20 . . . $1.70 . . . Pearl grey
3B0 857 563 BB41 . . . $1.70 . . . Black
3B0 857 563 B8YS . . . $1.70 . . . Light beige

http://forums.rennlist.com/rennforums/showthread.php?t=288836

944/951

Oxygen Sensor Ford Tauras 13913 http://forums.rennlist.com/rennforums/showthread.php?t=42959

944/951

Starter Advance Auto http://forums.rennlist.com/rennforums/showthread.php?t=276365&highlight=starter
951 Exhaust Studs / Intake bolts Saturn 11518152 Torx Tip
951 Fuel Pressure Regulator (FPR) 80’s BMW 5 series
BMW 13 53 1 711 541
Bosch 0 280 160 249
NAPA CRB219514 / BA 158024
Upgrade to 3 bar from stock 2.5 bar
944 Brake Pad Pins NAPA part # 82682 from a 1994 toyota T-100 pickup.

NAPA parts link

http://forums.rennlist.com/rennforums/showthread.php?t=303662
Bosch Cross Reference for all Bosch http://ecat-online.bosch.de/toc/frame1.html

For updates and comments, http://forums.rennlist.com/rennforums/showthread.php?t=297421

If anyone would like to claim/maintain this, please feel free.  I’m just reposting it because it disappeared.

Fix and flip: The Saga of the 2000 S10, Part 11

Today is going to be some final motor work and some cosmetic work.

The cabin fan sounded like it had mice living in there when it was on, so I pulled it out to see if I could get at the bearings to lubricate them.  No luck.  It’s just not worth the trouble.  I picked up another one for $30 and replaced it.  It’s not terrible to get at as far as these things go.

You have to move the ECU out of the way (silver thing on the right), remove its mounting from the coolant expansion tank, the expansion tank itself, and the frontmost stud that the expansion tank mounts on.  Two of the bolts (towards the fender) are pretty terrible to get at, and this is yet another “SURPRISE!  We decided not to use metric fasteners here!” area.  For the fan itself only, of course (they are 15/64).  The rest of the things you need to take out are all 10 MM.

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Fix and flip: The Saga of the 2000 S10, Part 10

It’s been a long time.  Too long.  At the end of Part 9, I mentioned that I had cross threaded the crank bolt.  What happened there was when I used the steering wheel puller to remove the crank pulley mount, I didn’t leave the bolt in place (it doesn’t interfere with the pulley mount), and the threaded rod of the steering wheel puller mangled the first few threads.  In an  attempt to make it easy to turn the motor over during the timing chain and head gasket jobs, I wanted to put the crank bolt back in with some shims (to ensure it wasn’t bottoming out on the back of the crank threads), and when trying to thread this in through the damaged threads, I made matters worse.

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Fix and flip: The Saga of the 2000 S10, Part 9 (It’s Alive!)

First up, let’s get a timing chain on this thing.  I’ve pulled the old gears, chain, and tensioner.  The oil cup plug has a hole in it. This is where the oil sprays on the timing chin to lubricate it:

There is a tech service bulletin out on this.  The new ones have a slightly larger hole to supply more oil to the chain to prevent timing chain failure.  So we need to get the old cup out and install the new one.

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