Hello jag-lovers, I’m working on my 86 series III again.
I bought my car off of craigslist and I believe it sat for a few years taking in some water through the sunroof. Quite a few of the electronic controls are corroded. Now that I have the car on the road and the engine is running well I wanted to address the AC/heater, neither of which work.
I’m not very concerned about the AC as I’m moving into winter but I don’t want to remove/damage anything that will make it hard to fix once summer swings back around. My goal is to greatly simplify the heater / AC by removing the climate control mechanism and make the temperature a more manual adjustment. I think many of the electronics are faulty and I’m not sure where to start. I have vacuum entering the car via the firewall but somewhere along the way it’s not getting “turned on” to engage the heater valve on it’s way back out to the engine bay.
I search the forum and found a few posts but I wanted to get some advice before diving in.
what exactly do you want to change and how much time do you have?
There’s a modification for bypassing the amplifier and sensor, that means that you have a switch that electrically changes your set temperature. It does this by running the small electric motor with attached clockworks, called the servo. In there, many electrical switches and vacuum valves are actuated by cams.
The servo can be heard when it is adjusting. I’d start by checking the fuse, whether the defrost function works, etc.
By removing the vacuum hose at the heater valve you should by default have a small amount of heat, but the flaps in the unit should be in a position accordingly.
If I were you I’d try to keep the whole thing standard as all modifications probably involve even more work. If there’s no whirring noise remove the two panels left and right of the transmission tunnel, be careful not to break the footwell vents. Seen from the right, the servo is crammed inside below and forward of the radio. The amplifier is hidden deep inside and has a round plug visible from probably the left side. First check if you have power to these and dis-and reconnect the plugs everywhere. Maybe also give the two knobs some usage, maybe they are slightly corroded and start working again. Some functions also come online only when coolant temperature is over 40°C or so. When the fuse is blown nothing works, which in my case happened because the wiring to the compressor clutch was… wrong. My bad.
There should be troubleshooting charts for the Delanair II as fitted to your Series III XJ.
Good luck and keep asking,
As David said…there is a manual control modification that bypasses all the automated sensing circuit. However, there is little that can be " removed" as the servo is what controls the fan speeds, flap positions, hot water valve etc.
Vacuum should enter on a white vacuum line and tee to the mode control switch and the servo. The mode control switch vacuum is the actuator for windscreen defrost flaps…the servo vacuum gets split into two circuits. 1 controls the hot water valve based upon servo cam position and 2 the dashboard center vents.
Cars that have sat for many years can suffer a couple of corrosion related issues. 1 corrosion to the fuse connectors, 2 corrosion to the feedback potentiometer, and 3 stuck climate control flaps.
There are infact 5 fuses that need to be checked.
15 amp climate control system power
25 amp fan blower power
1 amp amplifier
Inline fuse at Ranco Thermostat
Thermal fuse at AC compressor
To better assist you…i need to understand what is currently working. Once we know that…we can better target what maybe wrong.
Specifically; are fans actually running in ‘lo’, ‘hi’ and ‘def’ - and in ‘auto’. Fan problems must be solved as a separate issue - which usually are straight forward…
The system is operated by a servo, which use cam operated pushrods, vacuum valves and microswitches to position flaps etc as appropriate for heating and cooling.
The servo is controlled by an AC amplifier for automatic control - but the servo itself is essential for system function. A manual control is easily fitted to control the servo, bypassing the AC amp, which sometimes fail - and allow simple reconversion back if/when desired…
However, there is no practical way to make the system work without using the servo - whether heating or cooling. A defective servo ‘may’ be hand positioned to ‘heat’ position - but still require that the functions it controls are working…
Vacuum is extensively used, so it is essential that the system has vacuum - and that there are no malfunctioning vacuum actuators…
Basic functions are ‘easily’ tested - though remedial actions may be more complicated. But as Gary and David expresses it; what does the system do at present.
The first step is to get the fans running; if they are not (engine warmed up); the #3 (50A) and #6 (15A) fuses in the main fuse panel - clean cradle/replace fuses. Other fuses relates to the AC cooling functions - to be addressed when needs arise…
Thank you for the replies and sorry for not giving more details. Below is a summary of what’s working and not working. I’m not quite sure where to get a schematic of the internal vacuum lines for the heating system and electrical components. If anyone knows of a good resource that would be very helpful.
Working:
Fan - it works on all speeds regardless of the temperature setting.
Lower temperature control (under radio) - a cable moves a lever on the upper right side of the center console.
Vacuum to the water valve - there is always on vacuum to the water valve (engine compartment)
Not Working:
AC - doesn’t work, no troubleshooting
Vent changing - seems that the vents don’t switch from defrost to other settings.
Temperature doesn’t change regardless of dash settings
servo on the upper left side of the center console - doesn’t move regardless of settings
What I’ve done:
replaced vacuum lines and “t” fittings inside of console (I believe there were three)
replaced fuses (didn’t clean fuse contacts). I’ll add that to the todo list.
To review, since the fans work…you have a good main system fuse and fan circuit Fuse. Vacuum to hot water valve will keep valve closed so no heat.
Lower slide valve is only a face vent bias setting ( set to cold…you get slightly colder face level air. Set to heat…you get slightly warmer face level air).
Defrost flaps are controlled by a vacuum switch on the mode control knob…with vacuum…they should be closed…the fact that they remain open is either a faulty mode vacuum switch, disconnected pipe, or other system leak.
AC compressor -need to check inline fuse at ranco thermostat and thermal fuse at compressor as well as freon levels of charge.
I often suggest beginning diagnostics by confirming a functioning servo then move to other items
Remove the left transmissions vent cheek panel and disconnect the white octagonal plug. With probes, apply power to the female side of plug…i recommend using a 9 volt battery with clip on leads. Apply + to red, - to purple. Listen for servo “whir” if no response…servo could be at its limit switch, reverse connections…- red, + purple…now you should get response from servo. If no response…you will need to test at servo plug on right side…if still no response…servo requires replacement.
If servo functions…check vacuum connections at servo and verify they open and close the red and black pipes.
Next check Ohm value of feed back potentiometer. Connect digital ohm meter to orange and green of female side of amplifier plug…while connected, apply power to red and purple to cycle servo from limit switch to limit switch. Watch ohm reading…you want a smoothe transition from ~o Ohms to ~2.2 KOhms at each limit.
Please review the vacuum diagram and your connections and report back your findings.
**
Which actually closes the water valve, Adam - preventing circulation through heater core, and any car heating…
Disconnecting/clamping that vacuum hose to open the valve will likely not work. The heating/cooing is done b moving air flow flaps - directing more or less air though the heater core. In ‘full cold’ the air flow bypasses the heater core for maximum cooling. In addition, vacuum is applied to the water valve to close it…
So there is a suspicion that the system is stuck in ‘full cold’ - in which case the centre vents will be open, blowing ‘cool’; are they?
If the servo indeed does not move with temp set varioations; Gary’s suggestion to run the servo with an external source as he describes is a ‘must do’ first step! With the servo moving, it can be thus set ‘manually’ to test if you can get heat. Which then buy you some time for further musings.
If the servo won’t move; there is no appropriate way to make the system work. A replacement servo may be the best option - unless you have some nous in repairing things like that…
Gary’s point about the defrost vents is also highly relevant. They are held closed by vacuum - and should be closed in all switch positions except when in ‘def’ position. Loss of vacuum may be a switch or actuator fault, or you missing something when replacing vacuum lines. This problem must be pursued as it diverts air from proper cabin heating…
Do a preliminary AC test; with the engine idling check that the idle drops when switch is moved out of ‘off’. This confirms that compressor is engaging as it should - and the problem may just be lack of refrigerant. To be addressed at leisure…
The Dryer, this is a long metal can located on top of the radiator, has a small sight glass that can tell what’s going on inside the system. There are charts, just like reading spark plugs.
On the right side of the tunnel you can have a quick look at the vacuum lines and see what gets vacuum when. I should do this today.
My heater valve is disconnected and so is the compressor for now; meaning that I can choose between slightly warm and warm air using the flaps.
If your servo and feed back potentiometer pass the test Garry suggests, then next on the list is your A/C Amplifier.
It has an inline fuse (to ground).
If the fuse is ok, your Amp has a problem, quite common.
Apart from the vacuum switches, the electric part of the servo mechanism is quite simple actually, a multi-meter, and some nous of course, is all you need.
A motor, a potentiometer and a couple of diodes. All can be found in any electronics supply store for peanuts.
In mine one of the diodes had failed and as a result the motor would only work in one direction…
By using the 9 volt battery…you have bypassed all fuses. If testing was done from left side…you now need to move to the octagonal plug of the servo. The reason to do the initial test from the left is to verify all wiring in console. Now by testing direct to the servo plug…we can determine if the plug connections were the failure point.
Apply the 9 volt to red and purple again…and then reverse connections purple red. If servo still does not run…then the servo is suspect and must be corrected before proceeding further.
To remove servo, remove the vent extension with its screws. Mark flap rods against servo arms to assist with reinstallation. The servo is held to the heater box by a stud. The nut is inside the heater box and is accessable thru the vent opening…i believe it’s 8mm. There is also foam mounting tape between the servo and heater and may require gentle prying to remove. There is additionally a fixed locating pin toward the front…you will have to pull downward to free this pin. It’s a tight fit…but wiggle the servo out.
Note…no some early XJS and Daimler cars, the servo is held in with four screws…this style requires removal of the entire dashboard and heater assembly to remove…it is rare to find…but beware it exists if you don’t find the single stud.
Once out…check for burned diodes or bad motor…replace as necessary.
Thanks for the quick reply Gary. If I disconnect the servo plug (at the servo) and connect a multi-meter when and how much voltage would I see at the servo? I turned all of the knobs and didn’t see any voltage at any time. Is that expected? In addition to pulling the servo out and inspecting the electronics, I would like to verify the servo is getting the necessary voltage.
To answer your other question, “Auto” puts the fan on high.
With a working amplifier…the only voltage you should ever see to the servo is during amplifier “movement”. The design of the amplifier uses 2 relays…both normally to ground. When there is an imbalance in the sensing system…the amplifier switches one relay positive. Since one lead is positive and the other is to ground…the circuit is complete and the servo moves…once the sensing system is balanced ( via the feedback potentiometer value) the amplifier turns off the positive input to the relay…returning both to ground.
Disconnecting the servo…effectively removes the feedback pot circuit…shutting down the amplifier circuit. So you will likely never get a voltage from the amplifier to the unplugged servo.
The best test of the servo is to apply voltage to the red and purple wires to run the servo motor directly. + to red…- to purple, then reverse the connections. If the servo motor does not run with the typical “whirring” sound…it is considered defective until it can be sorted and repaired.
While the servo is out…it is the perfect time to test and service the feedback potentiometer if you want the fully automatic system operation. The manual control option eliminates the need for a functioning sensing system.
High fan speed in Auto strongly suggests the system is stopped in full cooling mode since med 2 and high are not available in heating modes. This “full cooling” would shut off the hot water valve and open the dashboard center vents.
Once you have a working servo…then the system can be tested for an operational amplifier.
**
If the AC is inoperative, the system will just use ambient air for cooling, David - which works perfectly…up to a point. But the flaps can only bypass around 90% of the air around the heater core…
I was able to pull the servo and verify that it functions appropriately with 12 volts. The servo works in both directions by reversing the polarity. I guess my issue is getting power to the servo. What would the next steps be for testing the amplifier and the different electrical components?
Adam,
You must confirm good connections on the molex pins on the servo / harness on all plugs.
You can tighten the female socket by using a small jewelers screwdriver and inserting between the plastic housing and the metal barrel of the connector. There is a gap in the barrel where the two edges come together. Gently pry inward on the barrel causing it to bend ever so slightly inward. Perform this task on all female sockets and reconnect plug. Now before reinstalling servo, connect plug and attempt to power servo from left side amplifier connector. If the servo operates… Reinstall and test system.
**
Power to the servo is normally delivered by the AC amp, Adam - and the only(!) test of the amplifier is that it turns the servo when temps are changed…
Basically the AC amp compares the resistance in the in-car sensor (varying with cabin temp) with the resistance in temp control (varying with temp set). Then powers the servo in the appropriate direction (heating/cooling) to change cabin temps.
It initially does this by setting the servo to max heat/cool - and when the set temp is reached, it resets the servo to a ‘blend’ position. As your servo works, as tested, the fault is usually the AC amp itself - and the standard procedure is to change the amplifier…
If this is not an option, going instead for ‘manual’ control of the servo by a suitable switch from a 12V source - no further testing is required. You just install the switch - there are pages of solutions in the Archives…
Further testing is only relevant if the AC amp is replaced, and it still does not operate the servo appropriately. Which either mean that the replacement servo is also defective - or the in-car sensor or temp control, or something else, is at fault…
@Frank_Andersen - I looked for about 30 minutes for the ‘manual’ control post. I can’t seem to locate it. Can you think of a few keywords I should be searching for? I would like to get a temporary manual fix in place as I’m getting a new amplifier.
With a momentary DPDT switch…this will do the trick. There are commercial options designed for the jaguar. Please remember this option requires a functioning servo and in car wiring and must be installed into the harness on the left side amplifier plug connection to be easily removable and not interfere with other electrical connections from the servo. Your biggest challenge will be to find a suitable location.
