A/C Clutch Harness Recall?

Cheers

As most early P38A owners will know, the air con clutch would occasionally not engage and eventually it slips and wears to the point where it rarely engages.

An early fix was to remove a shim behind the clutch but this only deferred the problem.

LR came up with a mod. kit, the aircon Compressor Link Harness mentioned above, to increase the applied voltage to the compressor clutch.

I removed the shim in mine about 7 years ago, and fitted the link harness about 3-4 years ago, and this cured the problem - I thought.

However, last week the compressor clutch failed to engage once more. The clutch had worn even more and the air gap was too great.

Following a suggestion from Scouse, I pulled the clutch off, put it in the lathe, and machined off 25 thou from the back of the clutch spigot. That reduced the air gap back to within spec (0.35-0.65mm) and all is well once more.

When I pulled the clutch off, I found it had been wearing unevenly so I'll keep an eye out for another one (secondhand from a failed compressor). Note the wear at the lower left:



The bit I machined down:

- and this harness is a 'snip' at almost £100; Guess it gets fitted after the shim TSB has first been tried (or the nth. customer has had a new clutch); Don't know how many folks actually have this harness but one easy way to spot it is a relay in slot 10 in the box.. anyone else with an older rig have this mod. ?

Early cars drove the AC compressor clutch directly from the HEVAC via the pressure switch but it was found that resistance in the various connectors meant that the clutch was often only receiving 9 or 10 volts. On later cars the HEVAC drives a relay that switches the power so this problem doesn't occur. If your connections are good you don't really need the harness. Usual high resistance connection is in the multiway connector behind the RH kick panel and also sometimes the connector on the pressure switch. You cannot simply put in a relay as the HEVAC checks the amount of current being drawn by the clutch so if it is only supplying a small current to energise a relay it will assume the clutch is faulty and not try to engage it. Hence the official loom having a big resistor to increase the amount of current being drawn. Later cars had a HEVAC that didn't check the current and an additional relay in the fusebox.

The alternator link is simply an additional heavy duty cable that is fitted between the alternator and the battery to supplement the original that goes via the starter motor.