Diagnostics
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. :-\