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>>>> 1999 S420 1971 Karmann Ghia Convertible
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Discussion Starter · #1 ·
My AC stopped blowing cold all of a sudden while driving on the highway. I ran the diagnostics and #7 = 0. I can't seem to bring up any DTC error codes. I followed the instructions but never see a blank screen.

Does a leak generate error codes?

Or do I recharge w/dye and find/fix the leak?

Thanks for looking.
Neil
 

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My suggestion is to hook up a set of gauges and check system pressure, If pressure is present then i would suggest taking it to a shop, have them recycle the refrigerant and replacing the pressure sensor.

If no pressure is found then most likely have a pin hole somewhere in the system and would use nitrogen and a ultrasonic leak tester to pinpoint the issue.

Either way..
i would take it to someone that knows how to do it since i seen ppl do several thousands dollars damage to their A/C system by trying to fix it them self.

the equipment is not cheap unless you can borrow it from someone.
good luck..
if you need some help or advice i will be glad to help as much as i can :)
 

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>>>> 1999 S420 1971 Karmann Ghia Convertible
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Discussion Starter · #3 ·
Adrian

Thanks for the pointers... and yes I will take in... AC is not to be fooled with by weekend motor heads... like me.

Thanks,
Neil
 

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Not a problem Neil...
I'm a certified tech and i seen the horrors of home A/C repairs !!
Blown up evaporators blown up drier cans...
I had a guy couple of years back that came in with a caddy and was wondering why his A/C wasn't working.
after a quick check i noticed that there was a large leak in the system. so i tried with the nitrogen but it did not even build pressure...
so i went over to compressed air cuz knew that there was a larger problem at this point.
Next step ?? ask customer what had happened.
so i go to him and tell him that there is probably a very large leak and what happened ( i maintained his cars ) as he start telling me that his nephew "tried" to top up the A/C system and put in 4 cans of refrigerant into the system at which he heard a loud pop.
what was the pop you might ask ??
it was the evaporator core that balooned up like a damm accordion and broke the heater box open and came close to hitting the heater core!
total cost of repairs ??
$450 for a used HVAC box and charge him $200 to replace it and all the orings in the A/C system and re-charge the system.

moral of the story is...
35psi on the low side and up to 150psi on the high side ( depending on ambient temperature ) not that every average joe knows whats going on in an automotive air conditioning system or for that matter how it functions.

if you want i can tell you what you need to try and fix it yourself..
but the tools would set you back a good $500 if not more!
 

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1999 S600 98K miles, 1994 E320 Cabriolet 13K, 2012 GLK 24K
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AC flush

After reading all these stories about the evaporators going out I am wondering just how common is this problem? (50 % chance 90% chance of going out anytime or is mileage a better indicator?) I have 55K on my S420 but it is 11 years old. Would it be beneficial to have it flushed out , new dryer put on and recharged as preventitive maintenance? :confused:
 

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>>>> 1999 S420 1971 Karmann Ghia Convertible
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Discussion Starter · #6 · (Edited)
Adrian,

Would a bad sensor shut down the compressor? If there is refrigerant shouldn't it still cool? What are the chances this is a line, or fitting as opposed to a major, ($$$), component? It had been sitting for a week, I got in it on a 100+ degree day, fired up the AC, (which worked normally), but within 20 minutes it started blowing warm then hot air. The car has 139k.

Thanks,
Neil
 

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ok..
John ->

The main failure for evaporators in not really refrigerant related but more to moisture than anything else. if you wan to do preventive maintenance the best thing you can do is make sure you drains are open and no plugged.
most of the evaporator cores fail due to moisture corroding the very thin evaporator core cell's. 90% of the failures that i have encountered were at the lower corners where it will actually leak down and the condensation pool.
If you want to go one step further you can take it to a garage and have the system evacuated and run under vaccum to remove all traces of moisture whithin the system and the oil. At this point depending on the size of the system new oil will be introduced and fresh refrigerant will be put back into the system.
Beware of the shops that use recycled refrigerant !!! This most of the time could do more damage to the system rather than having your old refrigerant in the system. I seen a lot of shops do this in order to "save" a buck where they recover your used refrigerant in the same tank as the fresh refrigerant which sometimes is and issue due to a lot of the times ppl spike their system with commercially available synthetic non CFC counterparts therefore just killing the efficiency of the refrigerant. Worst i seen was someone used Propane ( yes you heard me right!! ... don't ask why but it was frightening just watching him ) to top up the A/C system. In my old shop we had 4 cylinders - 2 fresh R134's and 2 were the recycled refrigerant that was to be returned for refining and decontamination. The main problem is with R134 is moisture, the more moisture in it the less efficient it is.

Secondly most of heater core failures are electrolysis related.
Ford at this time has a major Problem with this on the New Edge.
They have moved on from a simple chemical flush to a heater core replacement now after the hit and miss with the chemical flush, the only problem is the MAJOR shortage of heater cores and wait for the are 2-3 months... now that sux if you live in cold climates like Alberta where it can hit -40C in the winter :eek:

Neil ->
The Pressure switch in your case sensor is there to regulate compressor pressure by cycling the A/C compressor on demand.
On more simpler systems there are 2 switches :

Low Pressure - it opens the compressor clutch circuit and does not allow compressor engagement in case the system is low in refrigerant. By this the manufacturer protects the compressor for running dry and damaging itself.
Most manufacturers have the pressure set to equal or lower than 25Psi for cut off.
High pressure - this does the opposite of the low cut out switch. when pressure exceeds 120 psi the switch opens the circuit dissengaging the A/C compressor clutch not allowing to build pressure any further. this is why you hear the compressor clutch cycling.

HOWEVER !!!
this switch is bypassed when the A/C System is in MAX mode, which will ignore the high pressure in order to meet the demand of the end user.
This mode puts a large strain on the A/C components pushing them to their limits, BUT newer cars that have climate controllers have been programed to only HOLD this mode for no more then 15-25 minutes to achieve "control" state after which it will return to its normal operation.
This mode allows the a quick temperature drop for the comfort of the user.
 

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both pressure sensor and temperature sensor are located on the receiver dryer :D

Specs For Refrigerant Temperature Sensor:
'C - KOhms
20 < 13
40 < 5.5
50 < 3.7
60 < 2.5
70 < 1.8

You should see anywhere between 4.75V - 5.25V coming out of the Refrigerant pressure switch.
Good luck
 
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