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Date: Fri, 26 Dec 1997 19:39:53 GMT
From: Ywan Mason <ymasonnopsamsouth.net>
Subject: Re: saab 900 info needed


> ??? This means that the usual trick of turning on the fan by turning > on the AC (in case of near-overheat) which engages the fan while the > AC is running does not work with a 900? > Sure it does. But there is no sensor involved. The AC request from the switch turns on the cooling fans via the ac relay. The overheat switch in the top hose only interrupts the signal to the compressor and the , not to the rest of the system. As long as there is refrigerant in the system enough to satisfy the receiver drier pressure switch and the anti frost thermostat is closed, the fans will come on even if the overheat switch is open. The overheat switch in the top hose has nothing to do at all with fan operation, it only interrupts the signal to the compressor and the idle up solenoid on 8V engines (US Spec anyway). If the thermostat is the reason for the overheat, no amount of fan running will solve it. That is the reason we list the thermostat as a major service maintenance item. With a fresh thermostat, a bypassed time delay relay and a cooler fan thermosensor, the gauge stays at 1/2 even in 98 degree NC summers. In very cold climates where the ambient temp in the evaporator box opens the anti frost thermostat and cuts out the fans and the compressor from activation from the a/c switch, running on recirculation will warm the sensor enough for it to close, allowing the compressor to run to dehumidify the cabin and eliminate fogging. Of course very cold air from the outside is dry as well, so fresh air works too. Its just when you get in the car steaming from your morning shower and fogging the windows that the recirculation trick works to allow the compressor to activate and get the windows clear a little faster than fresh air. After they clear, switching to fresh air usually keeps them clear, if its not so cold as to overcome the cabin heat. Ywan Mason

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