# Radiator Cooling Fan After-Run System - testing after-run thermoswitch



## autopulse (Aug 11, 2007)

-1990 GTI 
-8v Digi 2
-W/ Air conditioning 
-equipped w/ 3-terminal rad.thermoswitch & After-run thermoswitch 
my gti was running hot about a week ago. as i checked the lower hose (feeding into the pump) i noticed it was cold.. so i drained the fluid and started checking the components, via my Bentley...
things ive already checked & have passed:
-coolant level was fine at point of overheating
-hoses are in good shape / no restrictions
-proper tension on coolant pump belt
-thermostat operates properly 
-radiator is clog-free
-radiator Thermoswitch, when manually grounded, operates fan at both speeds
things i have yet to do:
-check batt voltage from control unit to fan
-check expansion-tank cap for proper function
-check ignition timing
-test coolant pump itself
...So, at this point, ive noticed that when i manually ground the After-run thermoswitch, it does not start to run the fan...
(* After-run thermoswitch* = a cylinder head mounted thermoswitch used to sense excessive engine compartment temps. High temps closes the switch making a ground connection for the after-run control unit and operating the fan for up to 15 min.) 
... my bentley is telling me to check for batt voltage (approx. 12v) from the control unit (terminal 8/87) to the fan (terminal no.2 red/white or gray/black wire).
My issue is that i cannot locate the "control unit" .. the bentley states that its located on the fuse/relay panel - i must be blind








any help with this would be appreciated; id like to be driving the gti again... plus, just so you all know, ive already spent time with the search button http://****************.com/smile/emthup.gif 
thanks 
the gti:









_Modified by autopulse at 2:06 PM 1-28-2008_


_Modified by autopulse at 2:07 PM 1-28-2008_


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## kamzcab86 (Feb 14, 2002)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (autopulse)*


_Quote, originally posted by *autopulse* »_My issue is that I cannot locate the "control unit" .. the Bentley states that its located on the fuse/relay panel - I must be blind









AKA: Time control unit *relay* for radiator cooling fan after-run system (part #191955532A). On the Cabriolets it's in position 14; don't know about the GTIs.


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## autopulse (Aug 11, 2007)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (kamzcab86)*

^^^
OOOHHhhhhh




































thats embarrassing








thanks, now off to the garage http://****************.com/smile/emthup.gif


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## Jetta A2 1989 (Sep 7, 2004)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (autopulse)*

If the lower rad hose is cold, the rad thermo switch isn't going to kick on the fan, because the rad thermo switch isn't getting hot.
Are you sure the thermistat is good.


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## autopulse (Aug 11, 2007)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (Jetta A2 1989)*

well, i tested it in my kitchen w/ some hot water.. it started to open at the correct temp. i assume that its fine by that outcome. http://****************.com/smile/emthup.gif


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## Jetta A2 1989 (Sep 7, 2004)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (autopulse)*

Did you get all the air out of the system?
Is the small hose from the rad to reservoir flowing good?


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## kamzcab86 (Feb 14, 2002)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (autopulse)*


_Quote, originally posted by *autopulse* »_well, i tested it in my kitchen w/ some hot water.. it started to open at the correct temp. i assume that its fine by that outcome. http://****************.com/smile/emthup.gif









Bear with me here... Did you hold it/drop it into _boiling_ water and let it sit there for a few minutes to allow it to open all the way? "Started to open" could mean that it didn't open all the way, which means it's faulty.
FWIW, some folks, before installing a new t-stat, drill a pin-sized hole in the t-stat to ensure no air build-up; you might try that trick.


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## autopulse (Aug 11, 2007)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (kamzcab86)*


_Quote, originally posted by *Jetta A2 1989* »_Did you get all the air out of the system?
Is the small hose from the rad to reservoir flowing good?

yeah, its clear. thanks


_Quote, originally posted by *kamzcab86* »_
Bear with me here... Did you hold it/drop it into _boiling_ water and let it sit there for a few minutes to allow it to open all the way? "Started to open" could mean that it didn't open all the way, which means it's faulty.
FWIW, some folks, before installing a new t-stat, drill a pin-sized hole in the t-stat to ensure no air build-up; you might try that trick.










its true, i witnessed it open but did not measure it for accuracy








interesting tip as well, thanks every1 http://****************.com/smile/emthup.gif


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## autopulse (Aug 11, 2007)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (kamzcab86)*


_Quote, originally posted by *kamzcab86* »_
Bear with me here... Did you hold it/drop it into _boiling_ water and let it sit there for a few minutes to allow it to open all the way? "Started to open" could mean that it didn't open all the way, which means it's faulty.
FWIW, some folks, before installing a new t-stat, drill a pin-sized hole in the t-stat to ensure no air build-up; you might try that trick.









ok, i remeasured the t-stat.. it opens prematurely -at 175 (instead of 185)... and becomes completely open WAY before 212???
is my t-stat garbage???


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## autopulse (Aug 11, 2007)

*Re: Radiator Cooling Fan After-Run System - testing after-run thermoswitch (autopulse)*

its fine


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