On my 1986 560SEC, the #5 fuse would blow whenever I turned on the A/C (which blew plenty of cold air). Now, the A/C clutch does not engage at all. The high pressure switch turns on the fan, but there is no power to the low pressure switch. I researched similar problems in the archives, but didn't find these exact symptoms. I have the following questions:

1. Could the relay that operates the compressor have gone bad?

2. Where is it located (there are several identical relays in the fuse box)?

3. I'm going to run 12v directly to the A/C clutch terminal to see if it "clicks". Are there any other tests I should run?

Thanks in advance for the help.

Max J. Sandler

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M. Sandler

1986 560SEC: 150,000 miles, runs great, but I've got to sell it (too many cars for one man)
1987 560SL: 122,000 miles, used to run poorly, now (thanks to forum), runs great!
1997 GMC Jimmy: Turned out to be a turkey.
1989 T-Bird Super Coupe: 150,000 miles, still runs great. Ford got it right.

Someone out there is going to have to help me understand this one?

The clutch does not engage(essential to basic refrigerant flow) and the high pressure switch is running the fans? How could it kick in the fans if there's no pressure(clutch not engaging to drive juice)?

Sounds like some electrical diagnosis is in order.

I got the fans to work by jumping the switch; they don't work otherwise because the clutch doesn't engage. And you're right, it is an electrical problem. I thing it may be a relay, but I don't know which one provides 12v to the switch and the clutch.

Max

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M. Sandler

1986 560SEC: 150,000 miles, runs great, but I've got to sell it (too many cars for one man)
1987 560SL: 122,000 miles, used to run poorly, now (thanks to forum), runs great!
1997 GMC Jimmy: Turned out to be a turkey.
1989 T-Bird Super Coupe: 150,000 miles, still runs great. Ford got it right.

You might have too low a charge of R-12. There might not be enough pressure in the system to activate the low pressure switch which will cut out the compressor clutch. If you unplug the low pressure wires and bridge them the clutch should engage. Do this with the engine running and the AC on.

You might have too low a charge of R-12. There might not be enough pressure in the system to activate the low pressure switch which will cut out the compressor clutch. If you unplug the low pressure wires and bridge them the clutch should engage. Do this with the engine running and the AC on.

"If you unplug the low pressure wires and bridge them the clutch should engage. Do this with the engine running and the AC on."

I think the pressure is okay because there is continuity across the low pressure switch terminals. But there is no current to the switch, so the clutch doesn't engage. That's why I think it may be a relay in the system. All of the fuses are okay.

Max

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M. Sandler

1986 560SEC: 150,000 miles, runs great, but I've got to sell it (too many cars for one man)
1987 560SL: 122,000 miles, used to run poorly, now (thanks to forum), runs great!
1997 GMC Jimmy: Turned out to be a turkey.
1989 T-Bird Super Coupe: 150,000 miles, still runs great. Ford got it right.

Should be a relay labeled "KLIMA" (manufacturer) in the relay box, has about seven connections to it.

If you have a serpentine belt, there is a speed sensor on the compressor, so that if it slows down for any reason, the relay kicks out until you restart the car. This is to prevent the engine getting locked up by a seized compressor.

However, if it blows fuses, check for a short in the wire to the compressor clutch, it sounds like you have a ground somewhere in that wire. Also check for voltage at the wire (unplugged from the clutch) with a new fuse -- if there is voltage there, but the fuse blows when you reconnect the wire, the clutch is shorted and must be replaced.

I don't think a Klima relay will ground out and blow the fuse, but I'm pretty certain a short in the compressor wire will melt the solder in the relay, rendering it inoperative.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

There is no serpentine belt or, to my knowledge, a speed sensor. Initially, the A/C compressor would kick on for about 3-4 minutes before blowing the #5 fuse, which also controlled the blower motor. The system was blowing cold air for those few minutes. Then, it quit coming on altogether, and just the blower motor would run. Your theory that the "Klima" relay may have burned out due to a short in the A/C compressor clutch sounds plausible. I guess I'll try running a jumper directly to the clutch terminal and see if a) the clutch kicks in, and b) if there is an excessively high current draw.

Thanks for your input.

Max

__________________
M. Sandler

1986 560SEC: 150,000 miles, runs great, but I've got to sell it (too many cars for one man)
1987 560SL: 122,000 miles, used to run poorly, now (thanks to forum), runs great!
1997 GMC Jimmy: Turned out to be a turkey.
1989 T-Bird Super Coupe: 150,000 miles, still runs great. Ford got it right.

Serpentine belt is used on 6 cyl M103 motor. 8 cyls used multi-belt.