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Yes, that pin is V1 and drives the fans through the slow-speed resistor. (All pins are the same as the left half of the twin-fan/twin-temp-switch module.) My temp switch is definitely just a single switch with 2 terminals, so there's no TF at all. I'll check the central electric board, but I'm pretty sure the holes are still open to accept the other pins.
Hi J1NX3D,
I mention that relay in my thread https://rennlist.com/forums/924-931-...r-sort-of.html. It lacks the timer circuit, so the fans will run the battery dead if the temp switch fails closed. (On the other hand, the timer circuit can also fail and leave the fans on even with the temp switch still working correctly, so I'm not sure it's much of an improvement. That may be why Porsche switched to the 105.03, but oddly no one has it marked as superseding 105.02, so it's hard to know if it was meant for another application or not.)
Not having a ROM programmer nor willingness to pay $100 for a used set, I found hobbyroms dot com online.
I sent Stephan at hobbyroms the TunerPro 1986 951DME binary and the KLR binary in this thread and got chips back by mail in a little over a week. The 2732A chips were in stock and pricing was very reasonable and Stephan is super responsive.
I popped the DME EPROM in this afternoon and it fired right up.
Why should we even bother with a low speed fan at all? I can see it being used in the winter. but other cars that I've had, had twin fans that ran at high speed all the time. I can also see using one fan, then both when the A/C is on..some one please enlighten me. Thanks.
I've been beta testing the new FT9 SS Fan Relay for a few days. Results are interesting: in the 951 all seems to work appropriately, but the S2 apparently has an issue... but I don't think it's a fault of the new relay.
For both the 951 and the S2 with the ignition OFF, pushing the LOW fan test button runs both fans at SLOW speed and the GREEN test light is ON. Turning the ignition ON and pushing the HIGH fan test button runs both fans at the FAST speed and the YELLOW test light is ON. So, all is working OK for fan speed test purposes when the engine is cold and isn't running.
The 951 isn't currently drivable due to a clutch actuation issue, so I could only test operation while running in the garage. Running the engine until it warms up turns the fans ON at the SLOW speed (normal operation) and the GREEN test light is ON as long as the fans are running. This is as far as I went with testing on the 951, which looks like normal operation.
However, in the S2 something (radiator thermal switch?) may be malfunctioning. For my initial test the other day I drove around the neighborhood until the engine had warmed up but before the fans kicked on. I then parked, and with the hood closed and the fuse/relay cover removed so I could see the fan relay lights I observed what was happening. I may have missed the initial operation of the fans while exiting the car because the GREEN test light only seemed like it was ON for a second or so before it shut off, and after that the fans were definitely running on FAST speed. However, the YELLOW test light did NOT light up, apparently indicating the relay was not getting a signal via the thermal switch FAST connection.
Today I repeated the test with the S2, but this time while parked in the driveway. It took awhile for the fans to kick in (temp gauge at 9 o'clock). When the fans came on they did come on at SLOW speed and the GREEN light turned ON. So far so good... after 10 seconds or so the fans started to turn OFF... and the GREEN light turned OFF, but before the fans could shut off they immediately kicked into FAST speed... but the YELLOW light never came on (just like the first test). I let the engine idle for quite awhile and the fans stayed on FAST speed the whole time. I don't know what is triggering the fans to jump to FAST speed because the relay apparently thinks the fans should be OFF. Hopefully, Joe can sort this out... but it does look like I probably need a new radiator thermal switch (last changed about 60K miles ago in 2004).
Correct! Mine runs after turning off, until engine is deemed cool enough to shut down. THIS is how I've saved my engine - and burned out 3 batteries now.
I have an 83, with a functioning DME - after I learned my lesson to only run 92+ Octane in her! Lower, literally MELTED my original DME,
from heat generated to retard the spark, to burn even mid-grade. Race car engines are tuned to run high octane for the entire system to run like a top!
And to pass SMOG.
I don't think the post-shutdown run-on is going to do anything to save an engine. The water pump is no longer running, and the hot parts of the engine are above the radiator so there's going to be no convection to keep the water moving either. Mostly (I think) it's just done to prevent boil-over as the heat-soak transfers from the engine to the water and the pressure goes up.
One other thing of note: while the pins are definitely open, Porsche opted to cut/grind off the one of the pins that's attached to the relay that's not used.
The sockets marked in read are the ones used by the single-fan/single-temp-switch/double-wide-module. The one in yellow is the one trimmed off.
Why should we even bother with a low speed fan at all? I can see it being used in the winter. but other cars that I've had, had twin fans that ran at high speed all the time. I can also see using one fan, then both when the A/C is on..some one please enlighten me. Thanks.
Running the fans at full-speed all the time will radically reduce their service life. Also, Porsche goes out of their way to reduce the perception of "disturbances", the high speed fans just make more noise than low-speed. There is also a benefit to the low and high speed fan circuits being more or less independent. The low-speed fan circuit will most likely to fail first since it is used used the majority of the time. Having a redundant backup in the form of high-speed fans no doubt has save many engines form overheating. Unfortunately for the single fan late-model 944, this redundancy does not exist. IMO this was clearly done for no other reason than cost reduction.
One other thing of note: while the pins are definitely open, Porsche opted to cut/grind off the one of the pins that's attached to the relay that's not used.
The sockets marked in read are the ones used by the single-fan/single-temp-switch/double-wide-module. The one in yellow is the one trimmed off.
Thanks for posting the picture, it is good the provisions for the pins where retained. It will not be difficult to create a version of the Solid-State fan really for the single fan 944. I just need to get a hold of a single fan relay to reverse engineer there timer circuit. I just need to know long to wait before turning on the high-speed fans, the rest of the circuit is straight forward.
I've been beta testing the new FT9 SS Fan Relay for a few days. Results are interesting: in the 951 all seems to work appropriately, but the S2 apparently has an issue... but I don't think it's a fault of the new relay.
For both the 951 and the S2 with the ignition OFF, pushing the LOW fan test button runs both fans at SLOW speed and the GREEN test light is ON. Turning the ignition ON and pushing the HIGH fan test button runs both fans at the FAST speed and the YELLOW test light is ON. So, all is working OK for fan speed test purposes when the engine is cold and isn't running.
The 951 isn't currently drivable due to a clutch actuation issue, so I could only test operation while running in the garage. Running the engine until it warms up turns the fans ON at the SLOW speed (normal operation) and the GREEN test light is ON as long as the fans are running. This is as far as I went with testing on the 951, which looks like normal operation.
However, in the S2 something (radiator thermal switch?) may be malfunctioning. For my initial test the other day I drove around the neighborhood until the engine had warmed up but before the fans kicked on. I then parked, and with the hood closed and the fuse/relay cover removed so I could see the fan relay lights I observed what was happening. I may have missed the initial operation of the fans while exiting the car because the GREEN test light only seemed like it was ON for a second or so before it shut off, and after that the fans were definitely running on FAST speed. However, the YELLOW test light did NOT light up, apparently indicating the relay was not getting a signal via the thermal switch FAST connection.
Today I repeated the test with the S2, but this time while parked in the driveway. It took awhile for the fans to kick in (temp gauge at 9 o'clock). When the fans came on they did come on at SLOW speed and the GREEN light turned ON. So far so good... after 10 seconds or so the fans started to turn OFF... and the GREEN light turned OFF, but before the fans could shut off they immediately kicked into FAST speed... but the YELLOW light never came on (just like the first test). I let the engine idle for quite awhile and the fans stayed on FAST speed the whole time. I don't know what is triggering the fans to jump to FAST speed because the relay apparently thinks the fans should be OFF. Hopefully, Joe can sort this out... but it does look like I probably need a new radiator thermal switch (last changed about 60K miles ago in 2004).
Regards,
I think what is going on with the S2 is a small leakage current form the fan switch. In theory, there is enough current to activate the high-speed fans, but not enough to illuminate the LED. I have redesigned the fan activation circuit to account for this, I should have a new round of prototypes in a couple weeks.
Running the fans at full-speed all the time will radically reduce their service life. Also, Porsche goes out of their way to reduce the perception of "disturbances", the high speed fans just make more noise than low-speed. There is also a benefit to the low and high speed fan circuits being more or less independent. The low-speed fan circuit will most likely to fail first since it is used used the majority of the time. Having a redundant backup in the form of high-speed fans no doubt has save many engines form overheating. Unfortunately for the single fan late-model 944, this redundancy does not exist. IMO this was clearly done for no other reason than cost reduction.
-Joe
Hello Joe,
What would be the benefit for me to have a solid state relay, I have a 951 1986 twin fan of course. I deleted the A/C with all the parts that came with it (radiator, etc..)
Does these relays have the habit to fail like the ECU/fuel pump relay ?
05-15-2021, 05:13 AM
