Nube question: a/c clutch (compressor, air conditioning, ac) - PeachParts Mercedes-Benz Forum

littlerobot · #1 06-23-2010, 01:57 PM

My AC clutch isn't engaging. While inspecting the clutch I found the nut was no longer on the front of it. It must have wiggled off. The compressor is a Delphi with the number 4356 on it. I can find very little info on it on the web.

1. What size is the replacement nut?

2. Is it metric?

3. Could this missing nut be causing the clutch to not engage?

rrgrassi · #2 06-23-2010, 02:33 PM

I do not know the answers to questions 1 and 2...

But number 3, yes a missing center bolt can keep the compressor from engaging(if the clutch disk is too far away from the pulley), as will low or no freon pressure, a blown fuse, a bad relay, a failed compressor clutch coil, a bad CCU, or a bad electrical connection.

panZZer · #3 07-22-2010, 08:19 PM

Quote:

Originally Posted by rrgrassi

I do not know the answers to questions 1 and 2...

But number 3, yes a missing center bolt can keep the compressor from engaging(if the clutch disk is too far away from the pulley), as will low or no freon pressure, a blown fuse, a bad relay, a failed compressor clutch coil, a bad CCU, or a bad electrical connection.

A part car I just got (83 cd)had seven or so lime green replacement relays in the trunk Where is the ac relay located on the 80's w123's and whats an easy way for an ac noob to check if the clutch is engaging?

littlerobot · #4 07-22-2010, 09:03 PM

On the w123's (I assume you mean the ice cube relays) there is a plastic box on the driver's side of the engine bay. Take the cover off and there will be a couple of relays underneath.

littlerobot · #5 07-22-2010, 09:06 PM

Oh - and you can tell if the clutch is engaging by looking at the front of the compressor. If its engaging, it will be spinning. If the front of the compressor (the face plate is the clutch) is spinning, its working properly. If it's not engaging, you either have low pressure, a blown relay, or a faulty climate control unit. Other problems are faulty low pressure / high pressure switches, both located next to the receiver drier.

panZZer · #6 07-22-2010, 09:49 PM

So if I cut a pigtail from one of the parts cars What colored wire goes to the hot post on a spare battery and which colored one grounds to the car

littlerobot · #7 07-22-2010, 10:28 PM

I'm not sure what you mean. What is a pigtail and how will it help you diagnose ac problems? I guess I'm not familiar with that terminology.

Codifex Maximus · #8 07-25-2010, 03:10 PM

Quote:

Originally Posted by littlerobot

I'm not sure what you mean. What is a pigtail and how will it help you diagnose ac problems? I guess I'm not familiar with that terminology.

I *think* what he means is... he's going to cut a piece of wire off of one of his parts cars and try to bypass the climate control system to test the compressor clutch.

If it was me... I wouldn't go mangling possibly useful wiring harnesses just for some wire. Wire is too cheap. These old harnesses are hard to come by and are not cheap.

Codifex

Yak · #9 07-25-2010, 06:34 PM

Quote:

Originally Posted by dmenefee

The easiest way to check the compressor clutch is to turn the A/C on full and look at the center like littlerobot said. If it doesn't turn: do you have a full freon charge? Then worry about the electrics. You can hotwire the clutch directly to the battery and ground with the engine off. It will click loudly if the clutch engages. The missing nut would prevent it from working. It might click, but the hub is held to the keyed or splined shaft by the nut. The air gap for the clutch is adjusted by replacing shim washers on the shaft behind the center hub. The nut holds it tight and when the clutch energizes (engages) it pulls the center hub in to contact the pulley face. No nut and there isn't enough friction to engage properly. No point in testing farther until you replace the nut.

Mixing threads and questions: littlerobot's clutch was missing the nut and his clutch wasn't engaging; panzer's clutch may/may not have a nut but also wasn't engaging.

Also, the FSM and the Harrison manual describe adjusting the air gap for the clutch by using the installation tool, not shims. The nut may/may not be required. There was none on my Harrison R4 HR100T, nor is there one shown in that compressor/clutch manual. There is one shown in the FSM, so the nut may depend on the specific compressor/clutch manufacturer.

The compressor will work without a nut. The nut more/less holds the key in place. The key is also very tightly friction fit into the slot. The key is what makes the clutch turn the compressor, not the nut.

All that being said; the air gap on my clutch was probably closer to 2 mm than the recommended 0.5-1.0, so the nut may be important for maintaining a good air gap, but it's not used for setting it.