A/C help pertaining to Klima relay

[jon316]

So I have my 85 300D, it had a new ac system installed, worked great for a good time. Parked it for about 5 months. The switches were giving me issues so I got a new one. Ac was still not working. So I recently started troubleshooting(very tight schedule so usually only Saturday afternoons with like a 2-3hr window) and noticed the relay was jumped, as soon as I touched the relay the compressor kicked on. But the fan in the front is not. I did notice the mechanic that did the ac put a standard auto fuse near the dryer, 20amp. If I remember correctly he said that was for the fan. So I checked power and it wasn’t getting any. So got another fan, to then see it was now getting power. But is not at the same time! Intermittently I suppose. I tried to do some research but was sent all over the internet. Now I did read those relays are a bit of a pain, and also my RPM gauge doesn’t work and I came accross a thread that mentioned the rpm tying into that relay as well? Any advice guys. Do I just run the fan somewhere else?


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[Diseasel300]

The fan is triggered from a switch on the receiver/dryer. The tach signal feeds into the Klima relay to engage the compressor. If your tach signal isn't present (tach doesn't work), the Klima relay won't engage the compressor.

[jon316]

But it hasn’t worked since I’ve owned it, is that perhaps why they jumped the relay? I put a new cluster as the mph had issues too as well as oil pressure. All the gauges work well now except rpm. As for the fan I guess that is the fuse they put. Gonna follow the wiring.

Any ideas on the rpm issue? Is that common?


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[Diseasel300]

1985 gets its Tach signal from the EGR computer. It is a common failure item. Someone here (Funola?) has reported success simply bypassing the EGR computer with the signal coming straight out of the RPM sensor. Maybe he'll chime in, or you can search the forum.

No telling what they did to the fan. It was fused originally at the fuse box, not sure why they thought it needed another fuse unless they modified the wiring. The original system had the fan triggered off a temperature switch on the receiver dryer. It operated a relay in the fuse box.

[jon316]

Below are some pictures I had taken. The fuse was just put into those two wires. And then also the relay with the jump shown as well.









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[W126world]

I'm not sure about the "D's" but my '84 280SE (W126) has a single pole/contact 95-100 degree celsius (which I changed for a 80-85 degree version to prevent overheat in Australia's warm climate) that controls the "Thermo/Aux" Fan... if it's the original switch/sensor, it'll be the largest of the sensors that screw into the block and take their temperature from the coolant as it moves through the engine.
I hope that's some help

[jon316]

So ac is working obviously cuz of the jump. But the fan is not and when I try to wire it I hear this relay click....probably the case as the fan was working before, it would turn on constant once ac was on.




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[Diseasel300]

Is the fan wired back to that relay? Trace the wires and find out. If the relay is clicking, it is being energized. If you have a multimeter, measure voltage at the motor. If you have 12V, try applying battery voltage directly to the motor, it could potentially be dead. If you don't have 12V, trace the wiring back. If it dead-ends to that relay, see if you have 12V present at the relay terminals. If you do, the relay is probably bad. If you don't, move upstream and see if you have a blown fuse.

[jon316]

Found the in and out on relay connection and essentially jumped it, and fan works so I’m gonna give a wild guess and say it’s the relay. Now to jump onto the tach/egr issue


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[Diseasel300]

Originally Posted by W126world

I'm not sure about the "D's" but my '84 280SE (W126) has a single pole/contact 95-100 degree celsius (which I changed for a 80-85 degree version to prevent overheat in Australia's warm climate) that controls the "Thermo/Aux" Fan... if it's the original switch/sensor, it'll be the largest of the sensors that screw into the block and take their temperature from the coolant as it moves through the engine.
I hope that's some help

That's the overheat switch. The Aux fan is also triggered by refrigerant temperatures on vehicles with A/C. The Aux fan is primarily for helping the A/C condenser, not for cooling the radiator.

[jon316]

While I’m trying to service the ac I also noticed there’s air coming out of the defrost. It’s coming out of the vents too but looks like it’s bleeding off over the top as well. Another issue I have to look into. Can’t let this thing sit. Everything was working great prior to parking it!!


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[Sugar Bear]

PM sent

[ROLLGUY]

Originally Posted by Diseasel300

1985 gets its Tach signal from the EGR computer. It is a common failure item. Someone here (Funola?) has reported success simply bypassing the EGR computer with the signal coming straight out of the RPM sensor. Maybe he'll chime in, or you can search the forum.

No telling what they did to the fan. It was fused originally at the fuse box, not sure why they thought it needed another fuse unless they modified the wiring. The original system had the fan triggered off a temperature switch on the receiver dryer. It operated a relay in the fuse box.

My bro's 85 had the same problem. I did a Sanden retrofit on it, and the Klima relay was already jumpered. The EGR controller was removed, and found to have corroded contacts. The plug contacts were cleaned, and a replacement EGR controller plugged in. The tach works, and A/C works with the Klima relay (no jumper) now! The Klima wants to see the engine running before energizing the compressor clutch, so that is why the tach signal is needed.