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T-Cut · 27th January 2020, 12:37

It's unusual to hear of an original silver resistor lasting so long. Are you confident of the Demist Test result? The low speed should run continuously until you turn Demist off. A failed resistor causes the high speed to trip on after the aircon's been running a short while. This will then trip off and on every 15-30 seconds or so. The Demist Test should be run for a couple of minutes or more if you're unsure whether it's the low speed or high speed that's operating. The 'low' speed is pretty noisy.

High speed fan operation with no obvious temperature requirement can occur if the temperature sensor signal is missing or intermittant. One possibility therefore, is a bad connector or wiring to the temperature sensor. The sensor is screwed into the head on the RHS as viewed, just below the main coolant outlet. That's my suggested first check.

If the sensor and wiring is OK, then a fan running on after ignition off is usually a sign of an overheated engine. The 1.8 system can do so for up to five minutes. If it runs on longer than that, I'd suggest checking/cleaning the two connector plugs mounted on the nearside wheel arch (bumper off) also check the relays. Are you certain that this fan behaviour isn't due to a very hot engine? If there's any doubt, the best way to check is the Trip Screen Diagnostic routine which tells you the exact temperature in degrees Centigrade (the gauge on the dash is relatively meaningless). Here's a link to the Diagnostic routine: https://www.the75andztclub.co.uk/for...t=Running+temp

Another thing to check is the fan control box which is attached to the rear side of the fan framework. This contains the fan switching relays for high and low speed. Be aware that the fan system is on a permanent live feed. Earthing certain parts of the sytem may inadvertently cause the fan to run. To ensure safety when working on the fan system, remove the 80amp fusible link in the under bonnet fuse box.

You really ought to upgrade the silver resistor while the bumper's off. You can get the recommended 'gold' type from electronics outlets like Farnell, from forum traders and from ebay.

TC

27th January 2020, 12:37	#2
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,753 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	It's unusual to hear of an original silver resistor lasting so long. Are you confident of the Demist Test result? The low speed should run continuously until you turn Demist off. A failed resistor causes the high speed to trip on after the aircon's been running a short while. This will then trip off and on every 15-30 seconds or so. The Demist Test should be run for a couple of minutes or more if you're unsure whether it's the low speed or high speed that's operating. The 'low' speed is pretty noisy. High speed fan operation with no obvious temperature requirement can occur if the temperature sensor signal is missing or intermittant. One possibility therefore, is a bad connector or wiring to the temperature sensor. The sensor is screwed into the head on the RHS as viewed, just below the main coolant outlet. That's my suggested first check. If the sensor and wiring is OK, then a fan running on after ignition off is usually a sign of an overheated engine. The 1.8 system can do so for up to five minutes. If it runs on longer than that, I'd suggest checking/cleaning the two connector plugs mounted on the nearside wheel arch (bumper off) also check the relays. Are you certain that this fan behaviour isn't due to a very hot engine? If there's any doubt, the best way to check is the Trip Screen Diagnostic routine which tells you the exact temperature in degrees Centigrade (the gauge on the dash is relatively meaningless). Here's a link to the Diagnostic routine: https://www.the75andztclub.co.uk/for...t=Running+temp Another thing to check is the fan control box which is attached to the rear side of the fan framework. This contains the fan switching relays for high and low speed. Be aware that the fan system is on a permanent live feed. Earthing certain parts of the sytem may inadvertently cause the fan to run. To ensure safety when working on the fan system, remove the 80amp fusible link in the under bonnet fuse box. You really ought to upgrade the silver resistor while the bumper's off. You can get the recommended 'gold' type from electronics outlets like Farnell, from forum traders and from ebay. TC Last edited by T-Cut; 27th January 2020 at 19:13..