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A while ago the bonnet [hood] switch went south so I removed the fragments and put the replacement job on my cool season hit list. As most will be aware the switch engages the light under the bonnet when opened and it also prevents fan run on for safety reasons. My non stock twin fan setup is fully shielded so no real reason for the safety feature. However, although I am not worried whether the bonnet light functions or not, I noticed that my fans do not run on when the motor is shut down. Since I got the cooling system well sorted years ago the run on feature hardly ever comes on when everything is working as it should. Now, in my current situation with the switch broken and removed, am I correct in thinking that the run on feature should still work if the control logic determines it is needed? I am assuming it is just not needed but...?
if it was a push "in" switch , and you removed it , now electric connections are "open" as with open hood. Perhaps make a bypass on those as to simulate a "closed" hood ?
if it was a push "in" switch , and you removed it , now electric connections are "open" as with open hood. Perhaps make a bypass on those as to simulate a "closed" hood ?
As I can tell the switch contacts are normally open when the hood is closed. When the hood is open the piston rises under spring load and the contact is made - the bonnet lamp then illuminates as the circuit is made. When such happens, the logic knows "the hood is now open" so for safety reasons, it overrides the signal that allows the fans to run on if the temp sensor in the inlet manifold detects a temperature greater than 82C.
Thus, if as in my case that switch has grenaded, the system will not switch on the bonnet and will not stop the fan run on with the switch removed. As I understand the wiring diagram conventions, if the switch contact is shown open that is the position it normally resides in. So, according to the way I am interpreting it, the switch is normally open when the bonnet is closed and in my case that remains the same when the bonnet is open as well.
Just looking for confirmation I have this correct or if not, an explanation of how the system actually works if I have it wrong.
Wiring diagrams for your '93 GTS shows the switch is OPEN when hood is closed/switch pin is depressed. Removing the switch and isolating the connecting wire will disable the under-hood light. It may limit operation of the cooling fans in intake and/or transmission overtemp protection mode. Suggest that you jumper the intake temperature switch momentarily to test that. Some cars seem to have that function, some don't, in spite of the WSM description. Note that the alarm/immobilizer function from the hood opening will be lost with the switch removed.
On the fans function with hood open, I'm maybe 50/50 noticing systems that have the hood-open protection working vs. those that don't (including my own 1989 car). I haven't tracked it carefully by year, so no further guidance. It's easy to test just by connecting the two temp switch terminals with engine off.
Wiring diagrams for your '93 GTS shows the switch is OPEN when hood is closed/switch pin is depressed. Removing the switch and isolating the connecting wire will disable the under-hood light. It may limit operation of the cooling fans in intake and/or transmission overtemp protection mode. Suggest that you jumper the intake temperature switch momentarily to test that. Some cars seem to have that function, some don't, in spite of the WSM description. Note that the alarm/immobilizer function from the hood opening will be lost with the switch removed.
On the fans function with hood open, I'm maybe 50/50 noticing systems that have the hood-open protection working vs. those that don't (including my own 1989 car). I haven't tracked it carefully by year, so no further guidance. It's easy to test just by connecting the two temp switch terminals with engine off.
Bob,
Have to do some work on the fans tomorrow so will test the switch- I am pretty sure it will still run when the switch circuit is closed but we will see. The light comes on with the bonnet open as the circuit is then completed to earth so this suggests to me that the alarm circuit reads this as "normal" so if the switch is missing I expect the alarm will not function with the bonnet open as it has no means of sensing such. Car theft is something extremely rare over here- it is virtually non existent. The only thing like that I have experienced was one lunch time some 25 years ago. I left my Subaru in the car port with the doors open -when I came to return to work I saw the driver;s door was open- then noticed a cassette was missing- I would have paid the chap to pinch it- it was a CD my daughter left in the car [teeny bopper crap!].
I tested the inlet manifold switch for run on by shorting it out- nothing happened. Took the car for a run and then did the same test and the fans immediately switched on- thus concluded that the logic is that the engine temperature [more likely the coolant exiting the radiator] must be above a certain point for the inlet switch to trigger run on- makes sense as no point in switching on the fans if the engine is cold. Thus I concluded that the system works irrespective of whether the bonnet switch is functional or not. I also checked to see if the alarm is working and if nothing else the plunger on the door locking mechanism was flashing red so my assumption us it is arming.
The not so good news is that I thought I had heard a mysterious noise and when running the fans independently it was apparent that one my Spal fan motor units was making an awful noise. I quickly determined that it was the passenger side unit so pulled the thing apart. Turns out the SPAL motor is held together by a rivetted section so I drilled that out and the motor came apart quite easily. I took the disassembled motor down to a friendly workshop and the chaps there pulled the main bearing [which felt rough. They managed to find a replacement bearing from another shop close by and between us we rebuilt the motor using pop rivets to hold the bearing cap on- problem solved- $5 for the bearing and $5 for their efforts- far better than $400 for a new twin fan kit! The motor internals looked very well made, we cleaned off the carbon dust, rubbed up the commutator and then put it back together- getting the brushes out of the way of the bearing was tricky but we found a neat way to do that.
I reinstalled the twin fan kit, took the car for a brief run to warm things up and upon return the fans were running nice and quietly once more. Now I ave to decide whether to pull the other motor pre-emptively and do that bearing as well. Many yeas ago I discovered a quirk in the SPAL twin fan design in that the two motors had different weather proofing specs- bizarre. This makes me wonder if the motor that failed is the lesser of the two specs. Either way, if any of you have this kit installed it really is not too hard to replace the bearings if they get noisy.
Interesting thought on the manifold switch operation. The fan/flaps controller doesn't see water bridge temp, so the only 'engine is warm' detection available is via the temperature transducer in the bottom of the radiator on the outlet side.
I'll be in the system in the next couple days for coolant swap, and will have time to play with various switch, temp transducer and engine-run conditions on refill. Mine's not a GTS, but IIRC the operating requirements are the same.
Interesting thought on the manifold switch operation. The fan/flaps controller doesn't see water bridge temp, so the only 'engine is warm' detection available is via the temperature transducer in the bottom of the radiator on the outlet side.
I'll be in the system in the next couple days for coolant swap, and will have time to play with various switch, temp transducer and engine-run conditions on refill. Mine's not a GTS, but IIRC the operating requirements are the same.
Bob,
Assuming that interaction is correct I am sure it is responding to the value generated by the radiator sender as per the fan programme. I am sure your system will be same as mine. The only downside of my current situation is that the alarm would not sound if someone forced the bonnet open. Hopefully I can get a replacement hood switch or jury rig something if not available.
I'm troubleshooting a hood light that won't turn off (unless I switch the headlights off)...
I see 12 volts on the switch that I'm replacing. Whether the switch stays open or when I close it with a jumper (hood closed setting) the hood light stays on.
The wiring diagram seems to lead me to F23, then T22 then H6 and then I realize I don't know what I'm looking for anymore.
The radiator fan certainly runs when the switch is open - it's belt-driven. As for the light being controlled by a mercury switch - I'll give that a try. I'll also start the engine and see if anything changes when the switch is closed. Thanks!
the hood light has an internal switch, its a mercury switch , like the Thermostat switch in your house and will turn off once the hood is closed
'91 and later cars do not have the mercury switch for the under hood light and it is instead directly switched by the hood switch. On earlier (<'91) cars the hood light uses the mercury tilt switch - but only comes on when the marker lights are on - that is no longer the case for '91 and later - hood light is entirely independent of other lighting. From 1987 the hood switch was used for the electric cooling fan interlock, before that the main cooling fan was mechanical, (it never had an interlock for the separate Aux AC fan). The hood switch has been used for the alarm system (where fitted) since at least '84 (possibly '83 too?).
11-10-2019, 02:48 PM
Bonnet switch gone south
