Question for Electrical Engineers
Discussion
I'm trying to diagnose one of the million problems with my '83 Esprit. In the early years Lotus placed a fan on the engine cover in the back which is supposed to be triggered by a thermal switch. This (of course) is no longer working.
The circuit is not complex, but a little beyond me. www.driestone.net/mechanic/imgs/Fan_Diagram.jpg
I think it is possible that the timer is non-functioning, but I'm not sure (since I honestly don't understand what is going on.) I've thrown a multi-meter on some things to see if there are bad connectors (and of course checked the fuses and the thermal switch,) but I just don't see anything obvious that isn't working. I don't suppose anyone might be willing to give me a little guidance here?
The circuit is not complex, but a little beyond me. www.driestone.net/mechanic/imgs/Fan_Diagram.jpg
I think it is possible that the timer is non-functioning, but I'm not sure (since I honestly don't understand what is going on.) I've thrown a multi-meter on some things to see if there are bad connectors (and of course checked the fuses and the thermal switch,) but I just don't see anything obvious that isn't working. I don't suppose anyone might be willing to give me a little guidance here?
You saw Jim's response on the Yahoo list, right?
http://groups.yahoo.com/group/turboesprit/message/86249
From your schematic, it is difficult to tell what exactly is going on because the relays are only represented by the sockets, and not by what the actual relay does, that is, which are normally open, which are normally closed.
I'm gonna take some educated guesses here, follow at your own risk, etc., and say that you should try disonnecting the timer and jumpering timer plug pin 6 to +12v and see if the fan comes on. If not, then try timer plug pin 2 to ground at the same time. If anything smokes, as we say in medicine, YOYO (Your On Your Own).
I would venture to say that if the thermal switch is OK, and the inhibit switch (interlock) is OK, and the relays are OK by the fans coming on in the above test, then the only thing left is the timer. About $3 worth of junk parts from RadioShack should do it to replace one. Look for a book called "555 Timer Cookbook."
Dr.Hess
http://groups.yahoo.com/group/turboesprit/message/86249
From your schematic, it is difficult to tell what exactly is going on because the relays are only represented by the sockets, and not by what the actual relay does, that is, which are normally open, which are normally closed.
I'm gonna take some educated guesses here, follow at your own risk, etc., and say that you should try disonnecting the timer and jumpering timer plug pin 6 to +12v and see if the fan comes on. If not, then try timer plug pin 2 to ground at the same time. If anything smokes, as we say in medicine, YOYO (Your On Your Own).
I would venture to say that if the thermal switch is OK, and the inhibit switch (interlock) is OK, and the relays are OK by the fans coming on in the above test, then the only thing left is the timer. About $3 worth of junk parts from RadioShack should do it to replace one. Look for a book called "555 Timer Cookbook."
Dr.Hess
I'll take a stab at this convoluted mess.
The relay on the right side has it's coil to gnd. It is energized by the engine management closing the relay by supplying +12V to the coil other terminal when the engine is on. When the engine is off this normally closed relay passes power to the timer module. When the engine is running, power to the coil breaks the contacts of the switch thus disabling the circuit.
The relay then sends vcc through the center terminal to the timer pin 4. It also comes back through pin 2 to the relay on the left. That terminal is putting +12v to one side of that coil.
Whenever pin 6 on the timer gets dragged low (gnd) the relay on the left then closes. The fan then turns on until the relay is ungrounded by pin 6. The top pin on relay left supplies the voltage for the fan. This relay operates the opposite way in that it is normally open. When the coil is energized, the power flows to the fan.
There is also an inhibit switch which I assume is some sort of interlock for the fan in case the hatch is opened so you don't get your fingers cut off. This interlock supplies gnd or vss to the timer. Open up the hatch - no ground.
The other device is the thermal switch. Simple make break device calibrated for those temperatures. I assume the timer simply provides an on-time before turning things off to allow for compartment cooling.
I would check to make sure the inhibit switch goes to ground at the timer module when closed and that the thermal switch functions at something around those temps. Also try putting pin 6 of the timer to ground. Fan should come on. Then I'd check the relays. You'll have to chase with a meter but obviously make sure the two fuses are okay first.
It'd be nice to have pinouts for the relays but I'm pretty sure the terminals on the sides control the coils and the left has normally open contacts and the right is normally closed. I remember seeing some older Renaults that would quietly hum away at the curb for awhile all by itself. Guess the purpose of the timer is to save the battery.
Best guess I can make though.
Steve
(edited a little after a read Jims post that it is a run-on circuit)
>> Edited by arium on Sunday 11th July 02:59
>> Edited by arium on Sunday 11th July 06:52
The relay on the right side has it's coil to gnd. It is energized by the engine management closing the relay by supplying +12V to the coil other terminal when the engine is on. When the engine is off this normally closed relay passes power to the timer module. When the engine is running, power to the coil breaks the contacts of the switch thus disabling the circuit.
The relay then sends vcc through the center terminal to the timer pin 4. It also comes back through pin 2 to the relay on the left. That terminal is putting +12v to one side of that coil.
Whenever pin 6 on the timer gets dragged low (gnd) the relay on the left then closes. The fan then turns on until the relay is ungrounded by pin 6. The top pin on relay left supplies the voltage for the fan. This relay operates the opposite way in that it is normally open. When the coil is energized, the power flows to the fan.
There is also an inhibit switch which I assume is some sort of interlock for the fan in case the hatch is opened so you don't get your fingers cut off. This interlock supplies gnd or vss to the timer. Open up the hatch - no ground.
The other device is the thermal switch. Simple make break device calibrated for those temperatures. I assume the timer simply provides an on-time before turning things off to allow for compartment cooling.
I would check to make sure the inhibit switch goes to ground at the timer module when closed and that the thermal switch functions at something around those temps. Also try putting pin 6 of the timer to ground. Fan should come on. Then I'd check the relays. You'll have to chase with a meter but obviously make sure the two fuses are okay first.
It'd be nice to have pinouts for the relays but I'm pretty sure the terminals on the sides control the coils and the left has normally open contacts and the right is normally closed. I remember seeing some older Renaults that would quietly hum away at the curb for awhile all by itself. Guess the purpose of the timer is to save the battery.
Best guess I can make though.
Steve
(edited a little after a read Jims post that it is a run-on circuit)
>> Edited by arium on Sunday 11th July 02:59
>> Edited by arium on Sunday 11th July 06:52
I had the exact same problem on my S3. After eliminating the thermal switch, engine cover interlock switch, relays and the fan itself - the problem was the timer circuit. I replaced the IC's on the PC board and now the fan works fine. These chips only cost a a buck or two. The only labor is unsoldering the defective ones, this can be a bit tricky.
The two IC's are: 1. HEF4069UB (Hex inverter from Phillips Semiconductor) 2. MC14020B ("Q" flipflop). If you feel like tackling this job, I could get the chips for you if you are having trouble locating them.
If you could aquire a good timer from someone, you could confirm if your timer is good or bad. Install the known good timer, jumper the engine interlock switch and use your wifes hair dryer on the
bi-metalic heat sensor (located on the front, driver side for engine cover)being careful not to melt anything. The fan should run for about 15 minutues or so before turning off.
The two IC's are: 1. HEF4069UB (Hex inverter from Phillips Semiconductor) 2. MC14020B ("Q" flipflop). If you feel like tackling this job, I could get the chips for you if you are having trouble locating them.
If you could aquire a good timer from someone, you could confirm if your timer is good or bad. Install the known good timer, jumper the engine interlock switch and use your wifes hair dryer on the
bi-metalic heat sensor (located on the front, driver side for engine cover)being careful not to melt anything. The fan should run for about 15 minutues or so before turning off.
To make things a little easier to follow, I've taken the diabolical liberty 
of amending an excerpt from your drawing that may help clarify things:
This shows the standard European way of labelling relays.
Terminals 85 and 86 are the ends of the operating coil; 86 tends to be favoured by Lotus as the 'earthy' end.
Terminal 30 (or 51 as it's sometimes labelled) is the 'Common', or main feed to the relay.
Terminal 87 is the most commonly used 'output', ie whatever voltage is present at 30, appears at 87 when the relay activates. It is known as a 'normally-open contact', because whenever the relay is NOT activated, there is no output on 87.
Conversely, terminal 87a tends to be the least-used of the outputs in automotive applications. It is 'normally-closed', which is of course to say that when the relay is inactive, the supply voltage at 30 appears on 87a. This can be perhaps better understood in the following scrawled diagram, created by dipping a large spider in a puddle of oil in the driveway...
:-
In the left drawing, the relay is unpowered, and any feed at 30 comes out on 87a. With 12v applied to the relay coil, it 'changes over' and the supply comes out on 87. Simple
Ian
of amending an excerpt from your drawing that may help clarify things: This shows the standard European way of labelling relays.
Terminals 85 and 86 are the ends of the operating coil; 86 tends to be favoured by Lotus as the 'earthy' end.
Terminal 30 (or 51 as it's sometimes labelled) is the 'Common', or main feed to the relay.
Terminal 87 is the most commonly used 'output', ie whatever voltage is present at 30, appears at 87 when the relay activates. It is known as a 'normally-open contact', because whenever the relay is NOT activated, there is no output on 87.
Conversely, terminal 87a tends to be the least-used of the outputs in automotive applications. It is 'normally-closed', which is of course to say that when the relay is inactive, the supply voltage at 30 appears on 87a. This can be perhaps better understood in the following scrawled diagram, created by dipping a large spider in a puddle of oil in the driveway...
:- In the left drawing, the relay is unpowered, and any feed at 30 comes out on 87a. With 12v applied to the relay coil, it 'changes over' and the supply comes out on 87. Simple
Ian
Gassing Station | Esprit | Top of Page | What's New | My Stuff