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Old 06-05-2014, 02:03 PM
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126 condensor fan wiring mod?

Has anybody out there rewired the AC condensor fan to run whenever the AC compressor runs? In my 83, I want to run the control side of the fan relay through the compressor clutch to ground so that whenever the clutch is powered, the fan will run. My concern is that the 4ohm resistance of the clutch (according to the FSM) is too high for the relay to make. I suppose I could just try it, but I don't have Rollguy's Sanden upgrade kit yet. Trying to get ahead of the kit install. I wish I could just replace the stock temp switch with a lower one....

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Old 06-05-2014, 03:53 PM
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First of all, installing a different temp switch is possible. Not in the stock location, which probably would require a 14mm switch. But on the left side of your head, there should be unused bungs in the water jacket. These should take either 22mm or 16mm switches. If 22mm, Porsche or VW switches come in various temperature ranges. If 16mm, the switch from a 90's Honda will fit. I use a 92C fan switch from a Porsche. All you need to do is connect one terminal to a Y at the reciever/dryer switch, the other to ground.

If you want it on whenever the a/c is on, then short the switch on the receiver drier, and T the compressor wire to power the coil of the low speed relay. The relay only draws 1/2 an amp.
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Old 06-05-2014, 04:23 PM
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If I short the (freon) temp switch, the fan will run anytime the key is on. If I put a coolant temp switch in, it will run anytime the engine is warm enough. Like in the winter when the AC isn't on.
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Old 06-05-2014, 04:34 PM
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Originally Posted by resto108 View Post
My concern is that the 4ohm resistance of the clutch (according to the FSM) is too high for the relay to make.
How about putting the compressor relay (control side) and the fan relay on the same circuit?
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Old 06-05-2014, 06:10 PM
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i did the same thing for a while in my w123. but i did not like the idea of the aux fan running when at speed or on cooler days. it isn't really needed if you're going 30mph or so. it uses a good amount of amperage and it isn't a great idea to tax the charging system as it is marginal at best when stock. the silly temp activated switch on the drier is a joke in my opinion. i wound up getting a "red" w124 / late w126 PRESSURE switch that threads in the unused in your case location on drier. the temp switch just goes in to the body of the drier so you can remove it without losing any charge. but to install the pressure type switch, you will lose all of your freon. the red switch is meant for r12 but i like the lower turn on pressures. 210psi on, 160psi off.
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Old 06-06-2014, 01:19 AM
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Quote:
Originally Posted by resto108 View Post
Has anybody out there rewired the AC condensor fan to run whenever the AC compressor runs? In my 83, I want to run the control side of the fan relay through the compressor clutch to ground so that whenever the clutch is powered, the fan will run. My concern is that the 4ohm resistance of the clutch (according to the FSM) is too high for the relay to make. I suppose I could just try it, but I don't have Rollguy's Sanden upgrade kit yet. Trying to get ahead of the kit install. I wish I could just replace the stock temp switch with a lower one....
Here it is for a 123:
MOD- Condenser Fan & Compressor working together by adding a relay
A 126 is even easier, as everything is right there together (+12v @ GP relay, thermal switch, condenser fan connection etc).

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