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The lack of fan action is an obvious symptom to pursue, Jezabel - it is so detectable, and without fan action other faults masked to some extent.
Assuming, probably rightly, that you have the Delanair II, as Jan also indicates - it is listed for the Series II and III. The fans are activated by two different pathways; manual in ‘Lo’, ‘HI’ and ‘Def’, and via the servo in ‘Auto’ - that both fail to operate fans is ‘unusual’. Common to both pathways is the relay bank, the resistor unit and the temperature switch - vacuum is not involved in fan control…
The temp switch will ‘kill’ the fan actions while cabin heating, until the coolant temp reaches 40C - though it is principally overridden in ‘Def’, it must be checked. Locate the switch, clamped to the inlet heater core inlet water hose - bypass switch by connecting the two wires together - bypassing the water temp switch.
If nothing changes; locate the resistor unit - it can been seen above the water temp switch. The green/slate wire connects to the fans (and high speed relay); check power with a test lamp - it should be fully lit in ‘HI’ and ‘Def’, and the fans should of course then be running. If not, and applying 12V to the green/slate does not activate the fans - there is a connection problem to be pursued…
The relay bank connects to the resistor unit to vary fan speeds; the relays being operated by the function switch and the servo. The relay outputs can easily be checked at the resistor unit - for further diagnoses…if necessary…
As you have changed the relay bank with no change; and excluding possible misconnections; disconnect brown/white from the relay bank and verify, with a test lamp (100W in this case), that there is power to it from the 50A fuse. If no/low power, recheck fuse, and fuse OK; remove fuse holder and inspect connections. Due to the high current; a bad connection may overheat - disconnecting wires and/or cause damage to the fuse holder. In either such case; there is no fan power in any switch position - remedy as required…
The point of these checks is to eliminate possible causes - to narrow the range of suspects. Finding the actual fault is a bonus…
Of the other faults; verifying servo action is relevant - purple and red are the feeds to the servo, and as Jan indicates polarity reversal reverses the servo action. Power application should be brief to avoid possible servo excess - if no reaction initially, instantly change polarity. A low voltage battery could be used, if available - the whole point of the test is to verify if the servo is operational. I very seldom fails, but it has happened - but such a failure will not affect ‘manual’ fan control…
With lack of servo reaction, the first step is indeed to change the AC amplifier - it is the most common source of servo response failure. The reason for changing the AC amp is that it is easy - and without servo function; further tests are pointless. That the change had no effect may have 3 causes; new amp faulty, servo fault or an external problem. One external problem may be a blown 3A inline fuse that protects the amplifier - it’s behind the left hand side casing. Two connections alternatives were used; one with black wires - a ‘ground’ fuse…
…or ‘coloured’ wires, denoting a ‘power’ fuse - and there is some doubt as to different AC amplifiers being compatible with its ‘opposite’ alternative. There was a list exchange on this - which may be remembered by someone. Or it may be in the Archives. Ask list members specifically about this? Point being that the ‘later’ (‘Australian’) amp may not be compatible with the presumably early version used for the Series II…?
The compressor clutch engages whenever the function switch is out of ‘off’ - ie, it should engage when the switch is in ‘Lo’. You don’t specifically say if the fuse blows in this position, or if it blows only in ‘Auto’ - which may be pertinent.
The #12, 15A, is not specifically for the compressor clutch - it is the general fuse for the AC amplifier, which also controls the clutch. That the fuse blows when the AC is turned on (out of ‘off’) may be irrelevant for the compressor itself - to confirm; disconnect power wire at the compressor (usually green). If the fuse still blows, the compressor is ‘innocent’ - however; test the compressor clutch function (with the power wire disconnected) by applying 12V at the connection point. This can be done without the engine running; as power is applied there is a distinct ‘click’ as the clutch engages/disengages…
You are perfectly sane; faultfinding the AC set-up is very complicated - and can test the sanity and patience of anybody, testing is a painstaking process…
Salient points; the ‘manual’ fan functions are unaffected by the state of the AC amp and servo - and while vacuum is vital to proper AC function; it cannot interfere with fans or the electric components of the AC system…
Frank
xj6 85 Sov Europe (UK/NZ)
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