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As Gary says, Tom - what about the system behaviour apart from the non-action of the compressor…?
…the point being to sort out whether there is a particular fault - or the system simply sense that the compressor is not required under the present conditions. Crudely, if the fans do not run; the AC amp is unpowered - usually due to a blown 15A fuse. If the cabin temp is too low, or the system is stuck in ‘full heat’ - the system may decide not to power the compressor. If the ambient temp, as sensed by the Ranco thermostat. is to low - the thermostat will cut power to the thermal fuse…
Generally; the first step is to verify that the AC amp is operating the servo; turn AC to ‘auto’ and set the temp selector ‘65’ and then to ‘85’ repeatedly - allowing some time for the system to react. At change of temp, you should hear the ‘buzz’ of the servo moving. If there is no servo movement - there is no point in further tests; the AC amp has likely failed and must be replaced…
If the servo operates, and the system otherwise works as it should, heating and cooling the cabin; a specific fault affects the compressor clutch only. The point here is that the loss of the compressor, for whatever reason, only affects the systems capacity for cooling - it will try and maintain set cabin temp, and will do so unless ambient temps are higher than set temps…
I’m a bit surprised that you have the compressor mounted thermal fuse - later models usually had the pressure switch, and ‘most’ earlier version have converted to this more convenient set-up. Likewise, the inline compressor fuse may or may not be fitted, but if it is it should indeed be checked as Tony advises…
Basically; the AC amp controls the compressor clutch through the servo connections via the Ranco thermostat (and inline fuse if fitted). If the Ranco has failed, or indeed if evaporator temp is below +2C, the clutch remains unpowered. Indeed, it is normal for clutch power to cycle according to evaporator temps - switching the compressor on and off, usually unnoticed while driving…
Arguably, it is safe to bypass the thermal/pressure switch that protects the compressor itself - PROVIDED that the Ranco thermostat itself works as specified. The Ranco itself must NOT be bypassed (except briefly for testing) - so it is important to verify where the power is lost. The Ranco is basically an ‘on/off’ switch showing ‘make’ above +2C…
Frank
xj6 85 Sov Europe (UK/NZ)
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