Where is the thermistor on my 83 USA Turbo?

[SilverEsprit]

Not getting power delivered to the otter switch, so tracing the pink/green wire back to wherever the power comes from. Except I'm not sure where to find it. Diagrams in PDF service notes indicate a center console connector (not sure where that is) which continues to an ACU unit underneath the steering wheel, but I'm not sure how to remove the dash to gain access. I also heard my 83 actually doesn't have an ACU, but rather a thermistor inside an evaporator. So I'm a little confused.

[drdoom]

I'm confident your Turbo was equipped with a complete AC system, and that the ACU is to be found under the dash atop the forward end of the central tunnel. This position makes it a difficult thing to access, in general. The thermistor which senses internal air temperature for setting cabin comfort level is inserted into the ACU casing inboard airflow side of the evaporator, so that it will be exposed to cooled air.

Cheers  

[SilverEsprit]

Thank you, DrDoom. Any advice on how I might get in there to check things out? After visual inspection I don't have any immediate ideas.

[drdoom]

For the most comprehensive visual tour of your car's innards I can suggest you survey the Restoration threads and find Fabian's massive account of his complete Turbo restoration. You will find he has documented just about everything with great photos.

Cheers  

[910Esprit]

The thermistor/evaporator is a red herring as the fans should come as long as the AC is switched on - i.e., it makes no difference if the compressor is cycling on/off due to the thermistor.    There is some kind of control unit for the AC directly behind the black facia that has the rotary switch for the AC, although I doubt that will be the issue, as the Otter switch should have a permanent +12V feed regardless of the AC.   (maybe have a look at the wiring diagram for a non-AC car to see how that is achieved).

Removal of the dash is not a trivial exercise, so I would discount that option for tracing an electrical issue. 

Edited September 18, 2022 by 910Esprit

[SilverEsprit]

A few months ago the radiator fans came on with the ac only. Now they do not turn on under any condition. Trying to figure out what delivers power to the otter switch (since there is none, tested with car running). I ran a jumper wire today from pin 30 to 87a of the interior cabin radiator fan relay (lower right, next to the fuses) and fan turned on. Short term, I'm considering wiring a toggle switch to this relay but I'd rather fix the core issue even if it means a bit of surgery.

Edited September 19, 2022 by SilverEsprit

[Andyww]

Disclaimer: Dont know about USA cars but:
Assuming the same as other, the rad fans come on when the AC compressor is on, via a diode controlling the fan relay. But thats not the issue you have. The power to the Otter switch comes from one of the fused circuits. The fuse is the same one as feeds the heater blower. Not sure though as I believe USA cars electrical system is substantially different.

[SilverEsprit]

You may be on to something, as my fans don't turn on with or without ac. Any idea where this diode is located so I can check it out?

[Andyww]

Its behind the fascia but that doesnt sound like the issue. If the diode were open circuit it would prevent fans being on when the compressor is on, only. Otter sw would still work.

Does your car have the same two 4-fuse holders in the RH of the glovebox as UK cars (and maybe early US cars) have? 

[DrieStone]

Not sure if it helps, but I shorted the temperature sensor for the coolant in the engine bay which should trigger the relay. 

If the fans come on, you at least know the relay/fuses are good. If they don't then it's easy enough to swap this temperature sensor (the otter switch).

The diodes I see are only related to the fain fail light, etc. 

I recently replaced my temperature switch, but I don't recall seeing where the thermistor for the ACU is, but it has to be behind that center console (which requires a reasonable amount of disassembly to get to).

[Geeman]

Silver Esprit, did you sort this issue out?  I think I am having similar issues with my 84 US spec Turbo.  Last week the radiator fans were working but today they weren't.  Last week I had blower fan problems but that got sorted (I think I shorted a wire for the stereo).  The fans work with a direct feed so I know they are OK.  I also was able to use a spare battery and get the fans running from the relay socket (terms 87b and 87).  However, when I jump the otter switch, no fans.  Fuses are all good, relay seems good.  I got the engine up to temp and did a continuity check on the disconnected otter switch and it was good, so I am thinking the otter switch is ok.  I am now thinking it's an AC circuit issue and power isn't getting to the otter switch from the AC Thermistor Control Unit.  FWIW, my AC system is currently inop, no gas.  The fan fail light doesn't come on either.

Attached is the cooling fan wiring diagram.  Any help appreciated.

 

[Andyww]

The fan relay is supposed to be energised by the AC controller, or otter switch. It shows the AC compressor relay feed going via the diode bottom left, to the relay.

The otter switch also correctly goes to the relay but it only makes sense if the wire marked "To ACU Cont Relay, sheet 6" comes from a direct 12V feed. So you could meter for 12V at that point. What does sheet 6 show?

If the relay has been replaced with a standard changeover one rather than dual-contact one that would stop it all working properly.

[Escape]

I'll repeat my answer by mail, as it could be useful for other owners at some point:

First check if you have 12V on the GK wire to the Otter switch, but only with ignition on. You probably wont. Next check the ACU control relay (sheet 6), my guess is that is where the problem lies. You can put a jumper connecting 30 and 87a (middle one) on the relay socket to rule out the relay. Ignition needs to be on.
The fan fail warning light gets power from the same relay, so wont work either if there is a problem in that part of the circuit. If the relay checks out, you need to look at wiring.

The interior fans and AC have no direct relation with the cooling fans, apart from sharing a relay and the AC being able to activate the fans.

 

For reference, sheet 6 that shows both the Otter switch and ACU are powered from the same relay, with a feed from fuse 21 that also feeds the interior fan. So if the interior fan works, the fuse must be OK and the relay or associated wiring is the likely culprit.

ACU relay.pdf

[SilverEsprit]

Geeman, no I never resolved it. I was unable to locate anything deeper than the Otter switch on the vehicle. I also didn't find any guidance on how to remove the dash or center console , just that it was difficult. I'm currently driving with a workaround—a manual switch with wires plugged into the relay socket at left of the steering wheel. I do hope to find a way to open up the car to diagnose and fix the core issue.

[Geeman]

Well I found the issue thanks to Escape and Andyww's input.  The problem turned out to be the ACU Relay socket.  One of the female connectors that pushes into the back of the relay socket was pushed back too far and the relay pin wasn't making sufficient contact.  I managed to push the female connector from behind the socket as I pushed the relay into place and that brought back the contact.  I jumped the otter switch connectors and with the ignition turned on the fans ran.

[LotuStuart]

Its called the Otter switch because the fans come on as the engine gets 'otter.

 

I'd be careful about inserting live feeds where there is an unknown problem.

The problem could be a short that blows a fuse and protects (expensive electrical item).

If you short it out to get it working, you may be applying power to a non-fused (expensive electrical item) and get a car full of smoke as an indicator of a new and exciting problem!

 

[Escape]

The best way to add a manual switch is to put it in parallel with the Otter switch (which if I'm right is the name of the company producing the switch), much like the AC, to energise the relay. That way all the safeties remain in place and the current for the fans only goes through the relay and not through the switch. I have added a manual switch like that to most of my classic cars, just to be sure. And I regularly use the override to avoid parking when the fans have just come on (i.e. turn them on manually a bit earlier and park with a cooler engine).

[DrieStone]

I'm now encountering some difficulty here. A while back I tested to make sure my fans worked by adding a jumper to the otter switch wires. I've been working on getting the car running again, and today I was finally able to take it out after doing a bunch of fixes. The car was running hot and I verified that the fans on the radiator weren't running.

I discovered that the fuse was blown, but the replacement fuse blew just as quickly.

I remembered then that I replaced my entire AC switch (the previous owner had glued the switches to the controls and I ended up damaging the stock switch). As some know, if you look up the part number A082M6221F you end up with the newer version of the switch. I ordered one anyway.

I wired everything up (matching wire colors), but something's not right. I dug in and unplugged my "fix" and the fans will now come on (no blowing fuses). I'm confused why the temp control switch would be blowing fuses. The wiring diagram doesn't give me more info as to what the four wires are, but it seems odd to me that Lotus would have changed what each colored wire connects to.

Does anyone have any insight as to what I should be looking for here? Where is the thermistor control unit located? I'm not even sure what I should be checking to diagnose this. I assume that the thermistor control unit is grounding the red wire which is causing a short, but I have to imagine this is related to the temp control switch being wired wrong.

[DrieStone]

Now I have to take that all back. I tested both ends of the plug to see what was happening (for future reference, black and blue get shorted when the switch is energized, and the brown & yellow are the temp.

I reconnected everything and no shorts.

I'm left wondering what happened. Maybe another wire under the dash was getting getting shorted? I don't know. I'm probably going to reassemble and cross my fingers.

 

Total side note: I thought my HVAC fan wasn't working on high, but it appears that it only runs full speed when the car is switched to on (not aux). I'm going to assume this is by design. Another Lotus oddity.

[drdoom]

If you mean "accessory" when writing "aux" then I would suggest Lotus not so crazy in holding back fan operation in that state. Fans will draw plenty of current so best have the engine running for the sake of alternator output when they're on.

Cheers

[Andyww]

I have recently been investigating a problem with fuse blowing (3 times in several years) of the fuse which supplies the interior fans and the AC. Unfortunately this fuse also supplies the otter switch so if it blows there are no rad fans. (82 UK car, might be different on US cars)

I could not find anything wrong. I have separated the otter switch now, onto its own fuse.

But, the loading of the blower fans is 8 amps each ( I tested them) and the compressor clutch is 5 amps. You could double that for initial inductive-load startup peak. So my theory is, if the AC is already in the on setting, then you turn on the blower switch to full, all three items start at the same time which blows the fuse (sometimes). 

[DrieStone]

On 01/07/2023 at 23:46, drdoom said:

If you mean "accessory" when writing "aux" then I would suggest Lotus not so crazy in holding back fan operation in that state. Fans will draw plenty of current so best have the engine running for the sake of alternator output when they're on.

Cheers

Yes, I meant accessory. Brain mix up there.

I don't necessarily have an issue with it, but I was originally trying to diagnose a fan issue and I thought one was still broken after I fixed it (I was going to get back to it later, but when I had the issue with the radiator, I discovered the fan came on full speed on high when I turned the key to on).

The wiring of the fans is pretty weird:

• On low: Both fans run on low
• On med: One fan runs on high, the other doesn't run
• On high (except for key "on"): One fan runs on low, the other doesn't run
• On high (when the key is "on"): Both fans run on high

It's just interesting that not only can you not run the fan on high when the car isn't on, but high moves less air than even low when the car isn't on.

Also note that the fan relay does nothing except for when you switch to "High". Low and Medium uses the switch to supply power to the fans.

 

On 02/07/2023 at 04:16, Andyww said:

I have recently been investigating a problem with fuse blowing (3 times in several years) of the fuse which supplies the interior fans and the AC. Unfortunately this fuse also supplies the otter switch so if it blows there are no rad fans. (82 UK car, might be different on US cars)

I could not find anything wrong. I have separated the otter switch now, onto its own fuse.

But, the loading of the blower fans is 8 amps each ( I tested them) and the compressor clutch is 5 amps. You could double that for initial inductive-load startup peak. So my theory is, if the AC is already in the on setting, then you turn on the blower switch to full, all three items start at the same time which blows the fuse (sometimes). 

 

Interesting. It does seem like a failure mode.

On the US cars, however, the internal fans are on one fuse (#1), but the "logic" is on another fuse (#21). It does look like the compressor is also on fuse #21, but I can't seem to see anything else that could have caused the issue. There must be a worn wire or something under the dash.

From what I see, there's no reason you can't pull the otter switch out of the A/C loop onto its own fuse. Although, I may put a switch under the dash that energizes the radiator fan relay instead.

I suppose some of the irony is that one of my blower fans was seized and one radiator fan was partially seized because the shroud was bent out of shape and the blades couldn't turn. I freed up both motors, but neither of those should have affected the fuse for the otter switch.

 

 

[Andyww]

13 hours ago, DrieStone said:

"logic" is on another fuse (#21). It does look like the compressor is also on fuse #21, but I can't seem to see anything else that could have caused the issue.

 

 

On UK G cars we can only dream of having a fuse #21

[TCAG]

Similar challenge

-Key on

-Otter fan switch jumped, fans not functioning incoming voltage reading  82.7 (with otter switch jumped using 12v power probe radiator fans function as should)

-Interior blower motor not functioning and at fuse 21 reads 82.7 (remove fuse and 12v power probe fuse 21 interior blower motor functions as should)

-AC low pressure cut out switch jumped radiator fans not functioning, incoming voltage 82.7 (with AC switch jumped using 12v power probe radiator fans function as should)

Does ACU Control Relay shown on sheet 6 powers these item? looks like it does.

Physically, where is the ACU Control Relay in the 88 turbo Esprit?

 

[SilverEsprit]

I have gotten nowhere with this. No insights for removing the dash either. I ended up installing a manual switch, wired up to the relay left of the steering wheel.

Edited May 9 by SilverEsprit