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TXV or low refrigerant? Or something else?

pdrayton on Thu June 19, 2008 11:08 AM User is offlineView users profile

Year: 1983
Make: Mercedes
Model: 240D
Engine Size: 2.4l
Refrigerant Type: R12
Ambient Temp: 85
Pressure Low: -10
Pressure High: 150PSI
Country of Origin: United States

This has me way confused, but I'm sure someone here knows the answer.

Compressor off - low and high side are both around 100psi

Compressor on - low side drops to -10 (vacuum) and hi side goes to around 150-180psi.

The mercedes factory manual says hi side should be around 350psi at this ambient and humiditiy (55%).

So this looks like a classic "not enough refrigerant" situation right?

Except that when I switch the AC off, the pressures take about 10 minutes to equalize. So it is like the TXV is stuck, or is the taking a long time to equalize just a symptom of low refrig?

I'm stumped, and don't want to pull all the R12 out to replace the TXV if it is not the problem.

Thanks guys.

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1983 Mercedes 240D on R12 and WVO!
1192 Mercedes 300D 2.5 R134a
1993 Toyota Pickup converted to R134a

TRB on Thu June 19, 2008 11:41 AM User is offlineView users profile

I would pull the refrigerant and find out how much is in the system. What you described here is just a system pulling into a vacuum do to a very low refrigerant level.

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pdrayton on Thu June 19, 2008 12:55 PM User is offlineView users profile

Thanks TIm.

After calling 3 ac shops in town who all told me they couldn't take out the refrigerant becuase it was R12 and they weren't 'qualified' to work on mercedes, I thought I'd try a different route.

However, I have a question - is the slow equalization of pressures normal? Is it not an indicator of another problem? How would a stuck TXV behave?

Thanks

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1983 Mercedes 240D on R12 and WVO!
1192 Mercedes 300D 2.5 R134a
1993 Toyota Pickup converted to R134a

pdrayton on Mon June 23, 2008 7:34 AM User is offlineView users profile

Well, I found the problem - leaking condenser.

I got a propane torch and some aluminum rods and did a test weld on an old radiator. No dice.

anyone know the trick to brazing aluminum - do you need that special flux stuff? what kind of torch? the propane torch didn't melt the aluminum brazing rod very well.....
Any suggestions? Seems a shame to put in a whole new condenser for a tiny hole...

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1983 Mercedes 240D on R12 and WVO!
1192 Mercedes 300D 2.5 R134a
1993 Toyota Pickup converted to R134a

GM Tech on Mon June 23, 2008 7:54 AM User is offline

If you start "fixing" that tiny hole on your condenser- it will soon be a big hole-- and what is to say that there are not more tiny holes waiting to spring a leak? I've never known anyone to be able to fix a condenser--so I never try it-- just spring for the new one--

besides... it IS a Mercedes.......

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Mon June 23, 2008 at 7:55 AM by GM Tech

pdrayton on Mon June 23, 2008 11:01 AM User is offlineView users profile

yes, is IS a merc, but it is an 1983 and it's a beater which I won't have for much longer. $250 for a condenser is more than a 1/4 of whatI paid for it! Good car though. And since I'm using ES12 ($6 a can, 3 cans for afillup) I don't really mind if it leaks. If it does, then I can try again...

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1983 Mercedes 240D on R12 and WVO!
1192 Mercedes 300D 2.5 R134a
1993 Toyota Pickup converted to R134a

plongson on Mon June 23, 2008 4:51 PM User is offlineView users profile

Unfortunately:
There comes a time when expensive repairs out weigh the value of the vehicle. Modern air conditioning systems fall into the same category as engines and automatic transmissions.

Fortunately:
One can make the decision to continue driving said beater without air conditioning.


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Vibration Analyst in Power Generation

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