S2 Air Con Thermistor

[Lou R]

Hi All,

I've been restoring my Federal S2 Esprit for a few years now and have seemingly exhausted all means of finding a replacement A/C Thermistor.  I've checked with all UK and USA based suppliers (new and used) and have come up empty !  The original Thermistor that came with my car has a broken shaft - not much I can do with it other than replace it (I have no idea if the electronics are any good).  Has anyone come across this problem before ?  Can someone recommend where I might locate one (new or used) or perhaps have one to sell to me ?  Or maybe someone has a proven workaround ????  

Many thanks,

Lou R 

[ChrisJ]

I had to look up what a Thermistor is

Have you looked for it within the parts of other cars of the period? Elite & Eclat? Esprit Engineering have two parts listed for "Esprit, Esprit S3 Turbo" Thermistor part no: A082M4765J and A082M6408F - no idea if they are compatible, but with the A082 part number probably not. Shop at Esprit Engineering • Esprit Engineering - Lotus Heritage Repair Centre - Lotus parts online shop

What's the part number?

What does it look like?

[Lou R]

I would describe a Thermistor as an on/off switch that also controls the A/C temperature (depending upon how far it is advanced).  Part number is A0796013F.  I've attached a couple photos of the guts behind the dash switch.

Thanks.   

 

A:C Thermister 1.pdf A:C Thermister 2.pdf

[fjmuurling]

On 30/03/2022 at 15:58, Lou R said:

The original Thermistor that came with my car has a broken shaft

I guess you are referring to the broken potentiometer, is it the metal part with the 4 small lips attached to the black part as shown on your photos?

If so it is a potentionmeter with a switch, the value is usually printed / engraved on the metal part.

[drdoom]

6408F would seem to be what is needed.

[Lou R]

Thanks for the responses.  

Esprit Freek, I've tried to read the printed values on the base but it's very difficult to read given its age.  Using a strong magnifying glass I come up 6-7CK Ohms (maybe it's 6-70,000 ohms ?).  It's blurred enough that it could be anything.  

Steve, not sure what 6408F refers too.  Is that what's printed on your 79 thermistor ?  FYI, my car is 101S - one away from yours.  I did a quick search of "potentiometer 6408F" but didn't come up with anything.  Can you please clarify your reference to 6408F.

  Thanks so much for the help.

[LOTUSMAN33]

https://www.ebay.co.uk/itm/202760841088?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=zqrjy9xdQem&sssrc=2349624&ssuid=OZtQKJxuSZ-&var=&widget_ver=artemis&media=COPY
 

I fitted this one to my JPS, worked a treat 👍🏻

[drdoom]

Hey Louis, that's cool to connect with the subsequent car's owner! By 6408F I referred  to @ChrisJ's suggestions above, specifically the one identified as A082M6408F which would appear to be a thermistor for the Turbo. I would readily wager the same bit as provided on our cars. On the other hand if it is in fact the potentiometer which concerns you, search for a thread I posted several months back on dodgy solder connections, better still check it out in any case as I suspect failed joints there to be common. Easily fixed, by the way.

Cheers

p.s. - show us a pic of 101S? 

[Lou R]

Steve, the thermistors used on the later Esprits (noted above) look to be entirely different from those used on the S2.  I think my best option at this time is to first replace the potentiometer.  The potentiometer referenced by LOTUSMAN33 appears to be an on/off switch with no capability to rotate to decrease the A/C temperature (?).  Please feel free to correct me if I'm wrong - electronics are way out of my wheelhouse ! I searched the forum for your earlier thread but came up empty.  As I noted above, electronics are not my area of expertise so if anyone can recommend a potentiometer that will work in my car's A/C I'd be most grateful.  LOTUSMAN33, please correct me if I'm wrong about the potentiometer you referenced - sorry but I'm a novice here !

My car is just starting to go back together after a very long restoration.  The body came out of the paint shop about a month ago, the chassis is completed and the engine and transaxle have been rebuilt and placed in the chassis.  I'm hoping to mate the body and chassis in short order and then install the harness and the million or so other items.  Interior is also re-upholstered and ready for install.  I'll provide more photos as I progress.

 

Esprit Body.pdf Esprit Chassis.pdf

[fjmuurling]

The one LOTUSMAN33 mentioned is a potentiometer with a switch.

Part of the missing part of the potentiometer is still attached onto the PCB marked VR. Just try a 10 KOhm potentiometer with a switch (lineair) should be easily available.

[drdoom]

I took my A/C control board to a shop servicing PC and small electronics where the proprietor demurred from sourcing a new pot, perhaps because difficult to find a match. As I recall, the pot tabs are directly soldered to the PC board, no leads between. I had correctly determined a fault with cold solder joint failure at one of the connections, handily repaired by the shop chap.

 

Cheers

[LOTUSMAN33]

Yes it’s a potentiometer which I soldered back onto the original PCB.

[Lou R]

Interesting.  My potentiometer had 2 leads connecting it to the circuit board.  I surmise the PO somehow managed to separate the pot from the circuit board and decided to run some wire between the circuit board and the pot as an easier means to make the repair.  Regardless, my pot is broken so a new one is required.  Since the wires are already soldered to the PCB I think I might just as well solder the other ends to the replacement pot.  I'll follow Esprit Freek's advice and locate a new 10K Ohm pot.  Steve, thanks for providing the earlier thread - I like the improvements you made and suspect I'll do the same to ensure it doesn't vibrate loose over time. 

Thanks very much for helping me out !

Lou R

[fjmuurling]

The new pot/switch will have 5 connections, 3 for the pot and 2 for the switch. remove the old pot part from the PCB and fit the new one onto the pcb with the 3 connections. The 2 wires you have to connect to the 2 connections on the switch part.