I know a lot of forum articles have been written about the issues with climate control in the XJ6 cars, and I have read a lot of these articles, but I’m not getting any wiser, so I would appreciative any hint and tips that I can get.
I have an XJ6 SIII 1986 and the car has been in family ownership since 1998. When the car was purchased the climate control worked for most of the time, but after a few years it developed a fault that if the temperature control was set to minimum setting it produced cold air, but as soon as the temperature control was moved away from minimum, hot air started to come out. This was sometimes intermittent and my dad that used the car at the time didn’t think it was a problem, so it was left.
I have now taken over the car and I’m trying to sort out various issues.
At the moment there doesn’t seem to mater in which position the temperature control is set to, hardly any hot air comes out. I can also hear the whiring noise from the climate control servo unit on a constant basis, it never stops, regardless of which position the temperature control is set to. I’m also curious what controls the speed of the fan. I can set the fan speed to minimum and it’s working, but as soon as I set it to AUTO the fan is blowing with maximum speed, doesn’t mater if it’s hot or cold outside.
Reading a lot of the forum posts, everyone are saying that it’s the AC amplifier (C45402) that is faulty, but then I found one forum post where people were saying that if you can hear the climate control servo working, then the AC amplifier isn’t at fault. Maybe they are right maybe they are wrong.
Could there be an internal temperature sensor that is broken or what are your thoughts?
Andreas,
Welcome to Jag-Lovers.
Problems with the Delanair MK II Climate Control system are discussed here regularly, so there are likely to be hundreds of posts about this in the archives. Based on your post I would say that the probability that you have a failed A/C amplifier is at least 95%. Although some basic electrical troubleshooting is possible, the only way to really test the system is by installing a known good A/C amplifier.
The OEM units have a very high failure rate. There have been a few different kinds of aftermarket units produced that appear to be much more reliable. I restored the inoperative Delanair MKII systems in two of my XJ6s to fully operational heat and air conditioning. In both cases I needed to remove and replace the compressors and all the o-rings and get the refrigetant professionally recharged as well as install aftermarket A/C amplifiers.
The probability that your problem is due to a thermister failure is probably less than 1%.
There is only one aftermarket source of A/C amplifiers that I am aware of, Jag-Aire.com. I purchased one of their manual units to help me sort out the climate control problems in one of my XJ6s. I have no affiliation with Jag-Aire other than as a satisfied customer.
I agree with Paul Andreas, the Amp would be the most likely cause.
An other thing to check is the water heater valve, also known to get rusty, blocked and stuck.
There are inexpensive generic plastic replacements that work very well and it’s quite easy to replace.
Normally, in the AUTO setting the fans will work at Max speed until the system reaches the desired temperature.
**
Are you quite sure the servo runs continually, Andreas - and not confused with another noise…?
Basically; the AC amplifier delivers an error signal to the servo - turning it to the appropriate position, then stops (some half a minute +). It is the servo that mechanically controls the settings of flaps, vacuum valves, and microswitches etc - which controls heating/cooling to maintain the set cabin temp. The servo should only reset when the AC amp detects cabin temp drifts off…
As Paul says; it’s virtually impossible, a waste of time, to do meaningful diagnoses on a fault without a properly working AC amplifier…
…but servo motion is a key element in testing the AC amplifier. Ie, setting the temp control alternately to ‘65’ and ‘85’ should make the servo turn - then stop; each and every time. If not; the AC amp is considered defective. I have never encountered a servo that runs continually - and have difficulties visualizing what could cause it…so…?
Isn’t there a potentiometer of sorts in the servo unit? Something that tells the amplifier where the desired position is or at least where to stop. Also, DEF would need to know where ‚full heat‘ is?
I‘d think if that value was never reached the servo would never stop. Alternatively, maybe the servo is broken. You would need to pull the right hand panel (the vents are brittle) and see if it moves. Just guessing…
Would the amplifier reverse the servo motor if it was switched from full hot to full cold?
Are the defrost vents open? Maybe the system partially thinks it is in defrost somehow and blows full heat, full power.
Of course if the sensor (above the glove box) was broken… but even then the servo should eventually stop!
If the water valve was stuck then it would never get cold, but it would not be fully hot either - just a little warm in summer, bit cold in winter.
Thanks very much for your reply.
You are right, the servo run in intervals of every 30 seconds (ish), maybe I over exaggerated when I wrote that the servo runs continuously.
Reading what everyone have replied with, I need to get a new A/C amplifier first and take it from there.
Sorry to hijack with a question but since I have some climate control folks here… my 86 S3 AC does not work and I was looking for any sort of step by step debug list.
Sort of like the excellent lists available for starting issues and fuel system checks
In your initial post…you stated that the servo was running constant.
This is a significant concern. First, the servo unit has two limit switches…if the servo is running…it should only turn thru approximately 270 degrees. Failure of one of the limit switches would be a concern, however, the feedback pot on the servo should send a signal to the amplifier to stop the servo motor travel.
It is possible…and I have seen it on rare occasions…that the main drive gear on the servo gearbox has become free on the servo cam shaft. If that is the case…the servo motor would run…but not turn the fan speed switches, heat vacuum valve, or feedback pot. If this is the case…the gear can be drilled and pinned to the shaft…or secured with a loc-tite type bonding fluid.
I highly recommend doing some basic checks on the system with the amplifier disconnected to confirm basic system operation. You can go to: https://www.jag-aire.com/ja-16-details and download the manual and follow the sensing system test on page 6.
While doing these tests…you should be able to confirm fan speed, heater operation etc.
I wasn’t that far off! Nice.
I think it’s worth the few minutes; take off the two footwell vent screws and look at the servo: does it move, and does it change direction?
Visually it could be hard to see the cam moving…it really depends if the servo still has its plastic cover intact and present. But if the cam is moving…you should have fan speeds increasing or decreasing.
The first item to look at would be the flap actuator arms…and see if they move up or down. Although, that may not be the best option as usually a stuck flap is what causes the gear to come loose of the cam shaft.
As a side note…series III cars seem more prone to spin this gear. Series II cars seem to just snap the plastic cam lobe for rearward most flap lever…leaving it no longer responsive.
Randy,
I know of no checklist for getting an inoperative Series III XJ6 air conditioning system to work again, although I have done exactly that on two of my former Series III XJ6s, a 1984 XJ6 Vanden Plas and a 1987 XJ6 Vanden Plas.
Both of these cars had fully operational Delanair MK II climate control systems when I got them but unfortunately they failed during my long ownership and I returned them to proper functioning again. In both cases there was a complete loss of the R12 refrigerant and unpredictable operation due to failed A/C amplifiers and other components.
The general steps I followed in returning these two cars to fully operational climate control systems included:
I replaced of all o-rings using proper lubricant for the intended R12 refrigerant.
I vacuum checked the total systems to see if they would hold 30 inch Hg for at least a week, but they both leaked vacuum right a way.
I isolated, identified and replaced the leaky components which were failed compressors and hoses. This was very time consuming and frustrating work.
Once the systems held vacuum for at least a week I removed and replaced the receiver driers and had the cars professionally serviced with R12.
Once the cars held refrigerant I operated, tested and replaced failed components which included two OEM A/C amplifiers, one heater blower motor, one heater valve, one AISIN vacuum valve, and two mode selector microswitches.
Returning the climate control systems to proper functioning in both of these cars was very time consuming, frustrating, and expensive. Instrumental to this work was my use of the Series III Service Manual, S57 Electrical Guide, and Delanair MK II Service Manual. I learned a lot along the way and I am very glad that I did it.
**
There is a feedback potensiometer in the servo unit, David - it ‘nulls’ the signal from the amp when the intended position is reached…
Basically; the AC amplifier generates an ‘error’ signal to the servo by comparing the in-car sensor potmeter with the temp set one. Turning the servo to a position that quickly heats/cools cabin - and then keeps the servo in a position to maintain the cabin temp as set…
**
Which implies that the servo cycles between ‘full heat’ and ‘full cold’, Andreas - which is equally odd. Does it pause in between the cycles?
A functioning servo cannot rotate, it can only turn back and forth around 240(?) degrees. However mysterious; only the AC amplifier can power the servo - so whether the amp is reacting to faulty inputs or just wrongly doing its own thing, is moot…
Changing the servo is simple - it’s an unusual fault and a replacement servo, even faulty, is very unlikely to have the same fault. Finding an input fault is a wild goose chase - worthwhile only if the servo is innocent…
As an aside; the turning servo should produce some transient clues - in full cold the centre vents should open, and close in full heat…
Paul… thank you SO much for this detailed summary. I was afraid of this, but however expected this type of answer.
I need to study both of the docs you mention, but one basic follow-on question. I assume it did, but did some portion of your repair require you to tear apart the dash on the inside of the car? I am very hesitant to do so since the PO spent a fortune redoing it and I would hate to botch that nice work.
Randy,
I know of no checklist for getting an inoperative Series III XJ6 air conditioning system to work again, although I have done exactly that on two of my former Series III XJ6s, a 1984 XJ6 Vanden Plas and a 1987 XJ6 Vanden Plas.
Both of these cars had fully operational Delanair MK II climate control systems when I got them but unfortunately they failed during my long ownership and I returned them to proper functioning again. In both cases there was a complete loss of the R12 refrigerant and unpredictable operation due to failed A/C amplifiers and other components.
The general steps I followed in returning these two cars to fully operational climate control systems included:
I replaced of all o-rings using proper lubricant for the intended R12 refrigerant.
I vacuum checked the total systems to see if they would hold 30 inch Hg for at least a week, but they both leaked vacuum right a way.
I isolated, identified and replaced the leaky components which were failed compressors and hoses. This was very time consuming and frustrating work.
Once the systems held vacuum for at least a week I removed and replaced the receiver driers and had the cars professionally serviced with R12.
Once the cars held refrigerant I operated, tested and replaced failed components which included two OEM A/C amplifiers, one heater blower motor, one heater valve, one AISIN vacuum valve, and two mode selector microswitches.
Returning the climate control systems to proper functioning in both of these cars was very time consuming, frustrating, and expensive. Instrumental to this work was my use of the Series III Service Manual, S57 Electrical Guide, and Delanair MK II Service Manual. I learned a lot along the way and I am very glad that I did it.
Randy, follow Garys advice first. Establish that the system works mechanically before you tackle any AC internals. You don’t need refrigerant to run the system, only if everything else works and it doesn’t blow cool (looking at the sight glass and compressor clutch engagement is easy, though).
Gary is the best expert on fixing the system you can find.
Randy,
Yes, some disassembly of the center dash area was required to test, and remove and replace the failed climate control components. In order to access the large fan relay, AISIN valve, and A/C amplifier connector I removed the left cheek panel. In order to test the servo and fan motors I removed the right cheek panel. In order to remove and replace the failed mode selector microswitches I removed the ski slope, radio, and had to partially disassemble the lower front of the dash.
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two screwdrivers, needle nose pliers, carefulness and patience. You will start at the cheek panel and the vent is brittle.