VW Vanagon radiator fan always on

My 1990 Vanagon's radiator fan went on the other day. I had the factory AC running... air temp outside was around 90 degrees but the water guage
was no where near overheat area. It went into the high speed (very loud) mode and would not shut down even after the car sat for an hour or more. It was draining the battery so I had to disconnect one terminal . Even now, connecting the battery runs the fan in high mode.
I disconnected the 3-pin plug that goes to the dual temp thermostat switch on the radiator and it still runs. According to what I can determine. There are two relays. One for the low speed (or speeds as some say there are two lower speeds) and one for the high speed mode. I pulled the relay for high speed and it stops. I tested that relay and it is good. Contacts close when energized and reopen no problem. I assume this is a standard N.O. relay(?)
I'm stuck. If the fan still runs with the thermostat switch disconnected and the relay tests good then what gives? Something else is causing that relay to stay closed. I have no prints of the electrical circuit. Can anyone help?
George
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I came across an article on the Gowesty site that seems to indicate there may be an electrical connection between this high speed fan mode and the factory AC. That on very hot days the AC will cause the high speed mode to kick in even though the article states they can find no wiring to indicate this.
If this is the case there must be a thermostat in the back AC area that controls the fan.
Anybody know about this?
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Yes it could be the AC kicking the fan on, but it's been so long I can't remember where the switch is. Also AC being over charged will do the same. Follow the hi-side of the ac lines from the compressor and sooner or later you should find the pressure switches.

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I know I had to top off the AC coolant this year due to a slow leak and I tried to keep the levels within range of my crappy tester guage. Would letting some coolant out relieve the switch pressure or is it gone for good now?
The high speed fan did come on one other time this year a few weeks ago.. very hot day again... but went off soon after shutting down van. I've AC since no problem. Will air temp cause the coolant pressure to increase?
George
Woodchuck wrote:

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G.I.O. wrote:

I'm sure you didi this, but the simple things are often the problem ... make sure both AC knobs are all the way off.
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