Temp gauge.. does it stay at 90 or go between 90 and 110 when just sitting in traffic?
07-09-2005, 03:46 AM
#2
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You have discovered the Gremlin
No, not the American Motors thing, but THE gremlin of Audi TTs it seems.
There've been several recent posts, including one I started. I live in (hot, sultry, humid, dengue-feverish) GA. My 2000 TTQC was showing 115+ on the climate control (CC) display when I cued-up the ECT (engine coolant temperature). That's ~ 239*F! We'd tried everything, and then I discoverd two things:
195*F and 205*F
These two are the setpoints quoted by my senior tech at the dealership. Your first coolant fan (RS?) comes on at the lower, and the second fan comes on 10*F later. That's ~ 90-91*C and 95-96*C.
The culprit (gremlin) is usually the Thermistor embedded in the lower left of the radiator tank (DS- has a square fitting/guard where the electrical connections make up). I posted a thread that showed the offending P/N, and the NEW Audi/VW P/N. Shazaam!
Here in (you get the adjectives this time) GA now, I have yet to idle at higher than 96*C in stop-n-go traffic on a late summer's afternoon.
Quick test:
Idle the car up in the driveway. Manually set the CC to "LOW" on the temperature dial and as high/fast as you can make the fan go. As the engine warms up to 91*C indicated on the CC display, open up your engine bay and look at the radiator fans. They should eventually both be running at idle. Nice and fast.
Apparently the thermistor failure mechanism will allow the fans (or the fan control unit FCU, also called the AC control head I think) to operate sufficiently to make the CC work, but you'll notice a rapid increase in louver temperature as you idle. With my new thermistor, this is no longer a problem. We're hanging meat in GA!
So, hye thee over to yon stealership, and tell them you think the thermistor is kaput. Test it in your driveway first: a little objective evidence (vice opinion) never hurts.<ul><li><a href="https://forums.audiworld.com/tt/msgs/1305838.phtml">Thermistor replacement</a></li></ul>
There've been several recent posts, including one I started. I live in (hot, sultry, humid, dengue-feverish) GA. My 2000 TTQC was showing 115+ on the climate control (CC) display when I cued-up the ECT (engine coolant temperature). That's ~ 239*F! We'd tried everything, and then I discoverd two things:
195*F and 205*F
These two are the setpoints quoted by my senior tech at the dealership. Your first coolant fan (RS?) comes on at the lower, and the second fan comes on 10*F later. That's ~ 90-91*C and 95-96*C.
The culprit (gremlin) is usually the Thermistor embedded in the lower left of the radiator tank (DS- has a square fitting/guard where the electrical connections make up). I posted a thread that showed the offending P/N, and the NEW Audi/VW P/N. Shazaam!
Here in (you get the adjectives this time) GA now, I have yet to idle at higher than 96*C in stop-n-go traffic on a late summer's afternoon.
Quick test:
Idle the car up in the driveway. Manually set the CC to "LOW" on the temperature dial and as high/fast as you can make the fan go. As the engine warms up to 91*C indicated on the CC display, open up your engine bay and look at the radiator fans. They should eventually both be running at idle. Nice and fast.
Apparently the thermistor failure mechanism will allow the fans (or the fan control unit FCU, also called the AC control head I think) to operate sufficiently to make the CC work, but you'll notice a rapid increase in louver temperature as you idle. With my new thermistor, this is no longer a problem. We're hanging meat in GA!
So, hye thee over to yon stealership, and tell them you think the thermistor is kaput. Test it in your driveway first: a little objective evidence (vice opinion) never hurts.<ul><li><a href="https://forums.audiworld.com/tt/msgs/1305838.phtml">Thermistor replacement</a></li></ul>
07-09-2005, 04:05 AM
#3
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eBahn numbers for setpoints?
Thermoswitch -F18/-F54
-F54 between terminals 1 and 2: Closes at approx. 95C (-V7- switched to speed 1).
-F18 between terminals 3 and 2: Closes at approx. 102C (-V7- switched to speed 2).
Switching conditions - Engine Coolant Temperature (ECT) Waring Switch -F14-
Switch opens at approx. 118 C - compressor is switched off.
More tech-commentary:
Notes:
Coolant Fan Control (FC) Module -J293- switches coolant fan(s) -V7- to speed 2 whenever the refrigerant system pressure rises above 16bar (signal ratio higher than 45%) and when Coolant Fan Control (FC) Thermoswitch -F18- is closed.. If pressure falls below 12.5 bar (signal ratio lower than 37%) the control unit switches the fans back to speed 1.
Various versions of Coolant Fan Control (FC) Module -J293-, used in conjunction with high pressure sensor -G65- may be installed. At the time of publishing however, All TT equipped with -J293- / -G65- have version where coolant fan(s) -V7- speed 1 is always switched on automatically whenever the A/C clutch -N25- is energized (regardless of refrigerant system pressure).
The refrigerant pressure signal from -G65- is also input to the Motronic Engine Control Module (ECM) -J220-. This input is needed in order to react to variable A/C compressor loads dependant of refrigerant system pressure. This signal may or may not appear as a duty cycle on the read measuring value block display Repair Manual , 1.8 Liter 4-Cyl. 5V Turbo Fuel Injection & Ignition, Repair Group 01.
Check refrigerant system pressures page 87-133 .
AND-
Coolant Fan Control (FC) Module -J293- switches coolant fan -V7- to speed 2 in the following instances: 1) When Coolant Fan Control (FC) Thermoswitch -F18- is closed. 2) When A/C pressure switch -F129- is closed (between switch terminals 3 and 4). 3) When Coolant Fan Control (FC) Module -J293- calculates a refrigerant system pressure in excess of 16 bar (based on signal received from high pressure sensor -G65-).
My head hurts!
Numbers appear to differ slightly, and I suspect these are the coolant fan speed control setpoints, not the on/off setpoints. But you get the idea.
-F54 between terminals 1 and 2: Closes at approx. 95C (-V7- switched to speed 1).
-F18 between terminals 3 and 2: Closes at approx. 102C (-V7- switched to speed 2).
Switching conditions - Engine Coolant Temperature (ECT) Waring Switch -F14-
Switch opens at approx. 118 C - compressor is switched off.
More tech-commentary:
Notes:
Coolant Fan Control (FC) Module -J293- switches coolant fan(s) -V7- to speed 2 whenever the refrigerant system pressure rises above 16bar (signal ratio higher than 45%) and when Coolant Fan Control (FC) Thermoswitch -F18- is closed.. If pressure falls below 12.5 bar (signal ratio lower than 37%) the control unit switches the fans back to speed 1.
Various versions of Coolant Fan Control (FC) Module -J293-, used in conjunction with high pressure sensor -G65- may be installed. At the time of publishing however, All TT equipped with -J293- / -G65- have version where coolant fan(s) -V7- speed 1 is always switched on automatically whenever the A/C clutch -N25- is energized (regardless of refrigerant system pressure).
The refrigerant pressure signal from -G65- is also input to the Motronic Engine Control Module (ECM) -J220-. This input is needed in order to react to variable A/C compressor loads dependant of refrigerant system pressure. This signal may or may not appear as a duty cycle on the read measuring value block display Repair Manual , 1.8 Liter 4-Cyl. 5V Turbo Fuel Injection & Ignition, Repair Group 01.
Check refrigerant system pressures page 87-133 .
AND-
Coolant Fan Control (FC) Module -J293- switches coolant fan -V7- to speed 2 in the following instances: 1) When Coolant Fan Control (FC) Thermoswitch -F18- is closed. 2) When A/C pressure switch -F129- is closed (between switch terminals 3 and 4). 3) When Coolant Fan Control (FC) Module -J293- calculates a refrigerant system pressure in excess of 16 bar (based on signal received from high pressure sensor -G65-).
My head hurts!
Numbers appear to differ slightly, and I suspect these are the coolant fan speed control setpoints, not the on/off setpoints. But you get the idea.
07-09-2005, 05:01 AM
#6
The fan thermoswitch has been a problem on watercooled VWs/Audis since>>
the beginning of time. Seems they did no better with the TT. But just because they list an "upgraded" part doesn't mean it won't fail eventually too.
