Some non-Mercedes content, but I’m hoping some of the more experienced auto electricians here can help.
On one of my cars, I was trying to trace a noise in the engine bay, which led me to disconnect the electrical connector on the clutch of a GM A6 compressor. After reconnecting it, the compressor clutch no longer engages—and I also lost the interior blower.
Additionally, a buzzing sound (like a buzzer) started in the cabin, and the oil warning light began glowing dimly whenever I adjusted the blower switch from low to high.
I measured the voltage at the compressor clutch and got around 2.9V. However, if I jumped the clutch directly from the alternator, it would engage.
Looking at the wiring diagram, I noticed that the compressor is tied to a ‘fan cut-off relay,’ which I located under the driver’s kick panel. It's in a block of eight relays. To the left of that relay is a ‘fan control’ relay, and next to that is the engine run relay, which is the one producing the buzzing noise.
All the relays are identical, and swapping them made no difference.
When I measured voltage at the relay connectors:
I would assume all relays share the same power source. So what could be causing the low voltage on just one? Could there be a fuse or fusible link I’m missing somewhere?
The wiring diagram (pages 3 and 4) shows the relays in question. If anyone could take a look and offer some insight, I’d really appreciate it.
Thanks in advance for any help
On one of my cars, I was trying to trace a noise in the engine bay, which led me to disconnect the electrical connector on the clutch of a GM A6 compressor. After reconnecting it, the compressor clutch no longer engages—and I also lost the interior blower.
Additionally, a buzzing sound (like a buzzer) started in the cabin, and the oil warning light began glowing dimly whenever I adjusted the blower switch from low to high.
I measured the voltage at the compressor clutch and got around 2.9V. However, if I jumped the clutch directly from the alternator, it would engage.
Looking at the wiring diagram, I noticed that the compressor is tied to a ‘fan cut-off relay,’ which I located under the driver’s kick panel. It's in a block of eight relays. To the left of that relay is a ‘fan control’ relay, and next to that is the engine run relay, which is the one producing the buzzing noise.
All the relays are identical, and swapping them made no difference.
When I measured voltage at the relay connectors:
- Engine run relay: ~14V
- Fan control relay: ~14V
- Fan cut-off relay: ~2.9V (matches the voltage at the compressor clutch)
I would assume all relays share the same power source. So what could be causing the low voltage on just one? Could there be a fuse or fusible link I’m missing somewhere?
The wiring diagram (pages 3 and 4) shows the relays in question. If anyone could take a look and offer some insight, I’d really appreciate it.
Thanks in advance for any help
