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Old 07-11-2003, 06:14 AM
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Join Date: Jul 2003
Posts: 15
Aircon probs.

I turned on my air con today for the first time in a long time. The problem is is that nothing happened. Its an '85 126 280SEL.

I checked the fuse (#11), and found that it was quite hot. I also checked the voltage at the clutch, and it was 0v. I then shorted it to +12v very briefly, and measured the voltage again and it read +12v. After leaving it like that for a while, I noticed that the pipe running to the condensor was getting hot, but the other pipe wasnt changing in temp.

As soon as I switched the ac off and then on again, the voltage at the clutch read 0v again.

Is this a saftey device that if the refigerant is too low the system won't operate?

I also remember that before when I used to run the ac the rpm of the engine used to drop quite a bit, but now there is no change in the engine speed.

The compressor is a merc (nippon denso)original system.

Any help would be greatly appreciated!!

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Old 07-11-2003, 07:03 AM
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You said you jumped 12Volts to clutch and it measured 12V. That's fine, but the important thing is, did the clutch kick in when you jumped 12V to it?

Good luck,
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Old 07-11-2003, 07:10 AM
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Join Date: Jul 2003
Posts: 15
I didn't notice any change at all in the engine's rpm or any cooling, but the pipe running to the condensor did get very hot, and the other pipe was very warm almost hot. There was a spark when I jumped the clutch though.
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Old 07-11-2003, 02:57 PM
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Join Date: Jul 2003
Posts: 15
can anyone tell me where the LP switch is on this system? Is it n/o or n/c?

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Old 07-12-2003, 01:17 AM
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You can do it
Join Date: Jun 2003
Location: OC S. California
Posts: 120
check the Low Preseeure switch, generally it is on the Dryer/receiver. If the refregent is low the swich will not complete teh circuit for safty and compressor will not come on. Try to shor it and see if you can hear the audible click of the compressor clutch, if clutch does come on, then check in the sight glass. You will have bubles in the sight glass, if it is low on R12 ( I am assuming that you are on R12, if you have converted to R134, I believe you will not be ablet to see the bubles in sight glass).
Good luck.
87 420 SEL
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Old 07-12-2003, 08:20 AM
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Join Date: Jul 2003
Posts: 15
Hey thanks! Shorted the LP switch, and the compressor started working. I wanted to see if any bubbles where in the slight glass, but was worried to run it if its low on pressure. If I run it will it cause any damage to the system?

I assume that the system is running on R12, as I've never had it refilled since new, and that was in 1985!!

Does this deffinatly confirm that the system is out of refridgerant? what else can I check?
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Old 07-13-2003, 10:00 AM
Posts: n/a

Your instincts were correct. Do not run the compressor with lp switch not made. What you did indicates, but does not confirm that you have a low charge. You need to connect a gauge set to confirm. Since the system has never been touched, it is possible that you simply lost enough refrigerant through microscopic leaks that you could recharge and be good to go. There are some steps to take first.

Look everywhere you can get to for an oily residue at the compressor clutch and all connections. That's your preliminary search for leaks. Then connect a vacuum pump, pump down for ten minutes or so and close manifold valves and wait 30 minutes. If the vacuum did not go down then you don't have a large leak.

If you don't have a large leak, you should be able to add 1 0r 2 oz. of mineral oil, replace the receiver/dryer and recharge. It would not be a bad idea to put UV dye in the system at the time so that you can easily find a leak if you lose the refrigerant.

Good luck,
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