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Thread: Jim's MK2 Air Conditioning FAQ
07-07-2007, 01:29 PM #1
Jim's MK2 Air Conditioning FAQ
Finally posting this. I wrote this during the R134a conversion kit.
This is focusing on AC only. I think a seperate FAQ for the heater should be written,
as there are a few techniques to for diagnosing, repairing, etc
Organized as following:
- R134a Conversion Kit
If anyone has some extra good information to add, ideally PM me, so
I can keep retain some organization for this FAQ
Last edited by jdk_ii; 07-07-2007 at 02:12 PM.
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07-07-2007, 01:29 PM #2
The MK2 is an R12 system.
Standard issue AC system with a few perks.
The AC system is automatic. Using a few temp sensors (one inside the center console),
the AC system auto-magically tries to adjust it self to the selected temperature.
It's terribly complicated by looking at the electrical schematic. Well, it was the 80's....
It does have one nice mechanial benefit. It's externally regulated, and adjustable. This by the EPR valve.
The thing on the passenger's strut tower with a thin hard line connected to it.
This external regulation actually prevent evaporator freezing via pressure sensing.
Many newer cars have themal sensor on the evaporator to shut off the compressor when evaporator freezing is detected.
It does have some extra adjustment features, which use are in the TSRM.
The compressor is a 10P15C, which is designed for R12. Very common, even on non-Toyotas.
The important note is that it's the model. They came in different configurations (like ear mount, etc).
So any 10P15C is not interchangeable with the MK2.
And lastly, the vent CFM is average. One reason is the opening at the blower case for recirculate is rather small.
That's why when you turn it to "fresh" you get a bit more CFM.
The blower motor could use some more RPM, to make it more American car wind tunnel like.
Last edited by jdk_ii; 07-08-2007 at 09:22 AM.
07-07-2007, 01:39 PM #3
How long does a AC system typically last?
The industry average is about 7 years from when the car was new. Though there are always exceptions.
Pressure and temperature fluctuation wears the seals, parts, etc. In order to gain another 7 years,
it’s suggested to perform maintenance on the system before it becomes a problem.
Are rebuilt Nippon Denso compressors a good idea?
Not really. They do not have a very good rebuild rate. Mostly it’s the design.
This by a veteran compressor re-builder, who sold his company to Four Seasons. If you do buy one, make sure it has a good warranty.
If you want a rebuilt, the best compressor to rebuild is your working compressor. You are likely to do this if repairing the system (drier, new o-rings, etc).
Why does my AC compressor not engage?
Say your AC was recently working. Now, when you press the AC button, the clutch does not engage or even click to engage.
Well, it could be the clutch or something electrical. But most commonly, the low pressure switch,
inconveniently located by the evaporator core has detected low pressure, or is toast.
There is a wire feed that comes out of the evaporator case. One test is to short the pins briefly to see if the compressor clutch engages.
You can also check with an ohm meter to see if the low pressure switch ohms are too high (means low – no Freon pressure).
Why does my AC work better when I’m driving, but if at a stop, it is not that cold?
Sounds like your condenser fan is toast. It will engage when the AC is on. The factory fan is a weak breeze.
A slim Spal fan would be a good replacement.
What the hell is that dash clicking noise??
This is the DVV unit, located just north of your right shin bone (while sitting in the car, that is). The clicking noise is magnets hitting each other.
The AC system is “seeking” or "hunting" the temp you have selected on the temp selector.
The reason it clicks is because the temperature selector potentiometer is dirty, or just plain worn out.
Here’s how you can test:
Once it goes in to the psycho clicking mode, apply some pressure on the temp selector button, by pushing it forward. The clicking should subside.
Some have had good success at using potentiometer cleaner. Other times, it’s just plain worn out.
Where are the common leaks?
Two that seem to be common are the drier (round black cylinder next to passenger headlight) and the front of the compressor.
Next would be any of the seals. Lastly, evaporators have been known to leak, more so when they get frozen. Leaking evaporators are really difficult to detect with leak dye.
My AC system has been dead for a long time. Is it worth fixing?
What is evil to an AC system is moisture and running low on oil. The later you can see when disconnecting some AC lines, and finding brown gunk.
If your system was open to the elements for a long time, aluminum oxidizes.
Putting just new seals, drier, vacuuming and charging seems like more work and money for something that will likely go south after a while.
Are leaks sealers any good?
I would only consider doing this as a last resort, and if the parts are stupid expensive.
For example, the Mercedes 190’s evaporator is $1K and costly labor. Dealers suggest leak sealers as a temporary band-aid.
Fortunately, the MK2 evaporator, low pressure sensor is rather inexpensive.
Are AC systems a money pit?
Yes. Once you fix one thing, and another breaks, you are faced with an evacuation and re-charge.
And the AC industry is built around this fact. Once warm weather hits, people pay serious money to stay cool.
How can I determine "cheaply" what's wrong with my AC system
Since an AC system can be a money pit, it's best to determine operational characteristics.
Suggested tests (in order):
- Determine if your compressor engages.
- Check if you system holds a vacuum
- Check if your system can hold pressure
You can bypass the low pressure sensor by jumpering it. It's a connector
coming out of the evaporator (consult the TSRM for it's location).
Then briefly test if the compressor engages. If it does, that's somewhat a good sign.
For the non-DIY, contact an AC mechanic, and request a vacuum and pressure test. This will inidcate if the system is still tight.
Some shops have clear hoses for vacuuming, so you can see what kind of gunk is coming out.
This will size up if your compressor works and if you have any leaks.
If no signs of problems, it's worth getting a re-charge. R12 if it's affordable,
R134a otherwise (DIY can try the R12 replacements).
If you have compressor issues or leaks, you need to resolve them first.
Then you have to take it back for a vacuum, pressure test, and possible re-charge.
If you get a re-charge, and the high/low pressures look within range,
that's good. You may now have cool/cold air. If you don't, you now
have more to investigate (the time/money sucking sound).
That's why the conversion kit replaced almost everything.
Where’s the best place to get my AC serviced?
Well, if you know a good local mechanic who is very knowledgeable about AC systems, be his friend.
I’ve found that trucking AC shops is far better equipped for AC testing and repair.
Is leaving leak dye in the system bad?
Leak dyes are a bit caustic. So they have the effect of putting some accelerated wear on the system.
They also reduce the Freon efficiency a bit. It's not horrible, but obviously, not having leak dye on a tight system is better.
Is vacuuming a system for 30 minutes sufficient?
Note that AC systems operate under pressure. So, if you system can hold a vacuum, it doesn’t mean it can hold pressure.
The best technique is to find an AC shop that will pressurize the system with nitrogen to check for pressure leaks. Then
run the vacuum to see if it will hold. I know trucking AC shops do this. It's short time and money to ensure your system
is tight (yo!)
Leaves and twigs?
Very common in the evaporator case. The fresh air draft is inconveniently located just behind the wiper motor.
I've even heard of mice finding their way through there to make nests in the blower wheel.
Without pulling the evaporator case (reasonably big job), one can pull the blower motor out,
and reach in towards the evaporator to remove any debris. I was able to sneak a 1 inch vacuum line
in to vacuum some extra debris.
The end effect of this debris is preventing evaporator efficiency, lower vent CFM, and sometimes you will
get the moist leaves smell. :-\
Last edited by jdk_ii; 07-08-2007 at 10:18 AM.
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07-07-2007, 01:47 PM #4
What about the R12 replacements?
Personally, I don’t like them. In the medium/long run, they are more caustic against seals and parts than R12 or R134a.
From an economic standpoint, they make great sense if you don’t have the money (or time) to properly fix your AC system. Perfect for the DIY.
Say your AC system works, but you know it has a small leak. The R12 replacements are cheap money to keep your system blowing cold air.
I would even consider it for testing out a recently working system to diagnose leaks.
I will caution, many AC shops will not touch a car that was converted to a R12 replacement gas. Depends on where you live, and the mechanic.
Can I convert my stock AC to R134a?
Sure. You need to find an AC shop that knows how to do it. And be prepared that it may not create cold vent temps.
Expect a range between 45 to 50F. Typically on the higher end. Not great, but certainly better than having no AC on a hot day.
Average conversions tend to report fluctuating vent temps.
Why doesn’t R134a cool that well?
Actually, it does. The real issue is heat exchange. The stock MK2 condenser is not that efficient with heat exchange.
The MK2 factory condenser tubes are somewhat thick, and fewer in number for proper BTU exchange.
Plus the factory R12 compressor does not create the higher pressure that R134a requires.
Can I use my old hoses with R134a?
You can. What occurs is that after some time, R12 molecules are larger than R134a.
And they have a sealing effect to prevent R134a molecules from escaping.
In my opinion, it’s better to get some new R134a hoses made. Much better piece of mind.
What do I have to change on my car for R134a
The suggested practice is replacing your o-rings with R134a o-rings, and the drier.
There is one o-ring that is on the evaporator core (requires evaporator removal). If you do that, it is
very recommended to replace the evaporator thermostat.
Is there a direct replacement 10P15C R134a compressor?
Not easily available. Some rebuilders will claim (true or not) to use R134a internal seals when they rebuild.
The 10P17C compressors (ie, used on the MK3) did appear in some 93+ cars (the R134a conversion date).
The furball(s) here are finding one that can use a V-Groove belt (the switch to ribbed belts started mid-80's),
and has interchangeable compressor inlet/outlet plates. As you can see, interchangeability is not easy.
And the AC industry likes this.
I've added some notes to the conversion kit section on how I selected the compressor. This may be a future option.
Last edited by jdk_ii; 07-08-2007 at 09:52 AM.
07-07-2007, 01:55 PM #5
The R134a Conversion Kit
Why did you make the R134a conversion kit?
Two reasons. Once we found out how much it cost a MK2 owner to restore his AC system (ouch)
and the fact that R12 is stupid expensive (definitely in the North East).
So, Greg, Phil, Curt, Bruce and myself discussed what would it cost for a REAL R134a conversion, that would be new car cold.
Even though we have the Mk2 purist disease, we’re frugal, and not interested in spending such a large chunk of change to have AC.
After loads of research, pricing, contacting manufacturers, etc, the pricing look very attractive. In fact, way better priced than any R134a full retrofit kit.
Plus it was all new parts, including a new compressor. I used a Seltec compressor, which is used in trucking, and agricultural equipment.
How did it turn out?
Colder than I even planned. I would have felt successful at an easy 45F vent temp. 40F would be butter. The best recorded vent temp
was by Bruce, at 32F. Plus it had some nice features to ensure system reliability.
Do you plan on making the AC kit again?
Maybe. The project was incredibly difficult. Two main issues to resolve
are finding mfg vendors to handle the lines and mounting brackets.
Two vendors backed out at the last minute, which was a nightmare.
What compressor did you use?
I selected a Seltec direct mount compressor. These are used on a variety of non-passenger car applications.
The pulley clutch are interchangeable, so either a V-Groove or ribbed belt pulley could be used.
They have a stack of benefits. Runs either R12 or R134a, industrial strength,
quiet, smooth engagement, great rebuild rate, and the big benefit, price. They
were about $225 during the GB. For individual purchase, I've seen them
range from higher 200's, to near $400! (obvious price gouging).
They didn't bolt up directly, so I had to make some adapter plates. These plates facilitated
interchange between MK2's with 5M's (V-Groove pulley) or 7M's (ribbed pulley).
PhilD suggested that I put together a Seltec kit. Adapter brackets and
new hoses, for those that don't want to waste time and money on
rebuilt compressors. This might be a future possibility. I first need to get my clone working.
Last edited by jdk_ii; 07-08-2007 at 09:51 AM.
07-07-2007, 01:56 PM #6
Jim, excellent write-up on the AC system......now I finally know what that clicking under the dash was...LOLMike "P"
2006 Toyota Tacoma Pre-Runner longbed
07-07-2007, 08:58 PM #7
That answers alot of my questions1984 Supra, 7MGTE,3",Magnaflow,Sparco 383,Sparco Corsa,AGX,Koni,Addco,TSC bar,LJM,GC Coilovers, Eibach,T3 Camber, T3 RCA, T3 Steering Arms, Dobinsons, SuperPro,Rear Camber Mod,PST,16x8 Circle Racing,Cressida Lip,JK BBK,PG Power Brute LSD,Black interior,Griffin Radiator
07-08-2007, 08:04 AM #8
- Join Date
- Jul 2007
- Grayslake, IL USA
OK, I'm still a little confused about the best plan for someone in my situation: just got the car (I'm new to the MkII scene) and the system doesn't even engage the clutch, probably from complete lack of freon, since the car sat for years.
So I'm already resigned to dumping a lot of money into fixing this thing, including converting to 134a and buying a new compressor. But what compressor to buy? I didn't see any recommendation other than rebuilt Densos are not very good. And will the conversion kill a rebuilt Denso in a year, or only an old Denso that's been used for R12? (I'm very familiar with the one-year-to-gut-puking trend on converting R12 systems using the original compressor...)
It sounds like my best plan is to hope you make more of your conversion kits! What are the odds on that?
07-08-2007, 10:35 AM #9
Good questions. I've updated the entries to answer these questions.
The short answers.
- some compressors are rebuilt with both R12/R134a in mind. One will have to research whom does this, as it's not entirely common. www.ackits.com
has knowledgeable people that can help.
- I've added a lower cost diagnosis for those that have no idea the state of their AC system.
- R134a conversion lifetime is much based on the existing system, replacement parts, and who has done the conversion.
There are some nightmare stories...
- future kits. Maybe. This won't happen until winter. I'd like one of the better vendors supply a full kit.
Then they can offer it any time someone needs one. I'm certain the pricing will be far more than what I offered,
but in the grand picture, it still will be more cost effective.
The good news, is they were reasonably impressed with the response and at least said "maybe" they would consider packaging a kit.
07-08-2007, 01:57 PM #10
My question is this: how long can all the components sit unopened in the box until I finally get around to having someone install the kit? Shelf life???
Seriously - good work JDK - this FAQ should come in handy to print out and give to a would-be installer should I ever get around to it....Phil G.
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