As for the temperature setting pot I think it’s because once you set the temperature you almost never move it again, so they see very little use and they last for ever…
This might help:
https://drive.google.com/file/d/17D95d4zA2TzVGHqh3v-3PuP00AcFIugy/view?usp=sharing
Thanks everyone for your help.
Hopefully the info below will help someone else in any future search for a replacement temperature pot.
I reached out to a Jag enthusiast who pointed me to this 15k pot on ebay.
“Allen-Bradley JAIN200P153UA Potentiometer 15K-Ohm”.
It will be necessary to shorten and make the flats on the shaft and solder on the wire leads, but it should work electrically.
There are zillions of those things:
Thanks for all the help at this point.
I ended up finding on ebay a used working original temperature control pot.
I put everything back together including a used but working amplifier and servo control.
System seemed to work as I played with the temp controller and air was coming out of correct vents. Then after 15 minutes, I only had hot air to the bottom vents or defroster. The right hand knob still controlled correct fan speeds, but I could not control from cool to hot or vise versa. I was stuck on full heat.
Using the sensor system chart, I found pin 7 (blue wire) to pin 4 (white wire) is an open circuit. Same thing for pin 7 and pin 3 (brown wire).
Pin 9 (orange wire) and Pin 8 (yellow) readings are good.
Pin 9 and Pin 5 (green wire) readings are good.
Pin 1 (purple wire) and pin 2 (red wire), If I apply 12 volts and ground, I can move the servo from hot to cool, then back to hot from cool, but according to the chart, I am supposed to get 30 ohms with a max of 100 ohms. Instead, I’m reading open circuit.
How sure are you that it was a working amplifier?
**
It’s really the flap positions that controls vent temps, jdere - and which vents are open or closed. Flaps are controlled by the servo, of course - which in turn is operated by the AC amp. So Aristides question is very pertinent…
Pin 1(purple) and pin 2 (red) are connected to the servo motor via the servo’s connector 5 and 6 - and applying 12V/ground is the standard method for manual control of the servo. That the servo responds with such direct inputs means it is working - but several comments arises to your testing…
a. Ohming connected circuits is at best inconclusive - as a minimum; the connector must be disconnected.
b. Ohming an electronic circuit, like the AC amp is likewise inconclusive unless specific data are known
c. Ohming the circuits from the disconnected connector is relevant, but readings depends on the servo’s
position
d. 1 and 2 are outputs generated by the amplifier - feeding power into the amp by those wires is ‘not recommended’…
e. If vacuum as failed, generally or in part, the system will not respond properly…
The general test of the AC amplifier is to set ‘65’ and then ‘85’ and vice versa - while listening to servo activity. With no, or intermittent, servo action, the AC amp is deemed faulty. With two proviso; if the cabin temp is below 65F the servo will stay put in full heat - if above 85F the servo will stay in full cold. And if the temp selector has failed - the servo may not respond as intended.
That the system responded normally for 15 minutes may be one of those things - but also while idling it takes considerably time for the engine to reach operating temps…
So…?
Frank
xj6 85 Sov Europe (UK/NZ)
Well I could hear the servo motor run and adjust the flaps as I increased and decreased temperature control knob. I could also feel colder from center vent then as I increased the temperature control knob, the center vent had no air flow and bottom vents had very warm air coming out.
I thought one of the fuses blew but I checked all three and they are good.
Probably this amplifier is no good now.
Using the sensor system chart, I found pin 7 (blue wire) to pin 4 (white wire) is an open circuit. Same thing for pin 7 and pin 3 (brown wire).
Wouldn’t these circuits, which tested open, mean that these is an issue with the in-car temp sensor and ambient sensor? I’m guessing the amp won’t be able to move the servo without correct info from these 2 sensors.
When my A/C Amp failed it would work intermittently… sometimes all was well, sometimes nothing was happening.
Open circuit between pins 7 & 4 implies the temp selector is kaput… Didn’t you test it before you install it?
Between pins 7 & 3 that either the in-cabin thermistor or the ambient thermistor are broken.
Thermistors almost never fail though.
On the other hand you system briefly worked, so either there is a bad connection somewhere, something is wrong with the amp or something is wrong with the measurements.
**
With the connector disconnected, jdere, you measure the resistance through the temp control with 7 and 4 - it should vary depending on temp setting. If you get no variations through the temp, the temp control or connections have failed. Again, if the servo responds to ‘manual’ control it is working - the temp variations is basically effected by the mechanical pushrods’ connection to the heater flaps. The center vents are opened by vacuum as directed by a cam on the servo - it opens when the system is in ‘cold mode’. With the servo in the ‘heat mode’, the center vents are closed - heat is through the footwell vents only. Crudely, the AC amp interprets the combined resistances of the in-car sensor, the ambient air sensor and the temp control, and applies power to the servo to turn it as appropriate to alter cabin temps.
It is therefore important to supervise cabin temps with a thermometer - if the cabin temp is to low, the servo will reset to ‘heat’…
The 7 and 3 connections are more intricate - they go through switches and ohm readings will vary with function switch and servo positions. An open circuit here is inconclusive - and unlikely to be involved in your symptoms…
Frank
xj6 85 Sov Europe (UK/NZ)