Yep! It was activated by a simple microprocessor effectively but still more mechanical in process. One might term it the start of that thinking.

 

Nothing that fancy! The compressor got power from a relay controlled by a Ranco switch with a probe in the evaporator. It's about as "mechanical" an electric system as you can get. The solenoid was also powered by the clutch relay.

 

Glyn: regarding the AC in my Pale Primrose Mk2, it was, as Jagboi has correctly stated, installed by the selling Jaguar dealer in Winnipeg (Motor Sales) in 1966. The car was built on January 4, 1966 and dispatched to Canada shortly after. It was apparently not used in Winnipeg winters as it did not and does not have even a single sign of corrosion anywhere either on the body or the frame. I acquired it when it had just 16,000 documented miles on it. But Winnipeg summers can be brutally hot, ergo the AC installation.
Fully charged, the system produces very cold air (again, as Jagboi says) using the original York compressor. The point of this message is to say that the compressor cycling on and off is virtually imperceptible…in fact you have to be trying hard to feel it and even then you aren’t quite sure…I found that an unexpected bonus. I have experienced cars in which the cycling of the compressor is indeed very noticeable, as you suggest, but the 3.8 Mk2, at least this one, isn’t among them.

While this may be irrelevant to the discussion, the car remains on its original positive ground and has had only two upgrades: a Pertronix ignition unit (but using the original Lucas distributor) and an electronic SU fuel pump which looks identical to the original points pump (it’s hidden anyway). It now has less than 28,000 miles on it. But your advice about fuel pumps caused me to purchase the Hardi unit. It sits on the floor of my study…I’ll get round to it one day.

 

Thank you for the input Prof. I have not experienced a York on an XK engine ~ only other brands. The crank, damper & flywheel weight on an XK obviously ameliorate what I don't like about clutched compressors. The XK is an unusually smooth running engine due to the above mentioned. The Mercedes 200 & 230E W123's 4 cylinder engines were particularly irritating units in this regard. The wonderful punchy 280E twincam 6 was a whole different matter. I too run a Pertonix Ignitor hidden in my distributor cap.

 

I think the extra air system in the series XJ is to maintain the idle speed of the engine when the compressor is working more than smooth the bumps as the clutch engages and disengages. An XK will idle happily at very low revs, but, if you add in the air con on a hot day and then turn the steering wheel quickly to load the steering pump, there's a risk of stalling the engine, which isn't very pleasant on an alpine bend ...
​​

 

In Oxford? lol.

 

Believe it or not, there was a time that I used to go on holiday. On a very hot day in Sardinia, the engine of my Daimler stalled crawling around a steep uphill bend. Steering a heavy car at that speed without engine driven PAS requires significant strength. Fortunately, fear of stone walls and shear drops generates surprising muscle power even in an 11 stone weakling.
​​​​​​
​​​​​​It was my own fault as I hadn't pushed the slushomatic into bottom gear.

 

Slightly off subject but I have had issues with the PAS at low speeds. I have the Marles Adwest Variomatic on my S Type. Unfortunately my car is an Auto. Not that the auto is bad, on the contrary it is very good (BW35) but the PSI for the system is driven by the speed of the PAS pump and if you are on low revs (Auto tick over is 600 RPM) the pump is not turning quick enough to produce the PSI to make the steering light. In a manual you just blip the throttle but with an Auto this is not possible without lurching forward and hitting the thing you are trying to manoeuvre around. Glyn has suggested replacing the pully on the front of the Generator for a smaller one to create more RPM to the PAS pump but I have not got around to trying it yet.

 

Your other far more complex route is to go in the 420 direction and run the 1200psi Saginaw pump as they did with the Varamatic. But I think you will run into space problems. The 420 has a crossflow radiator and more space on the carb side of the engine with the squared up nose.

 

Many of the PAS rack conversions use an electric pump adapted from the Vauxhall Astra. It probably needs an alternator if you don't already have one. I've always used two foot driving on older automatics: left foot brake, right foot throttle. It makes everything easier once you are familiar with it and, for maneuvreing at low speed, allows a dab of throttle. It's not advised with modern autos as it may confuse the electronic brain. In fact, modern ones, or at least my XK, don't seem to need it, but I still cover the brake with my left foot. A lurch forward from most Jaguars could wipe out a row of houses.​​

 

The problem you might encounter with the 1200psi Saginaw pump is with the higher PSI you might be more prone to leaks.

I left foot brake on a regular basis and often hold the car on a left foot brake as a handbrake for hill starts.
I don't know if it is normal as my S Type is the oldest Automatic car I have owned but I find that if you have your left foot on the brake and dab the throttle to lift the revs it won't. It is almost like the torque convertor has locked up the gearbox and the engine speed cannot rise as the rear wheels are locked. Doesn't stall the engine but it certainly does not lift the engine revs. In the winter when the engine is cold I often have problems pulling away up a steep hill near my house. You just can't get the engine revs up with the gearbox in gear and the car stationary. In a manual you would just feather the clutch and lift the revs until the car is moving.
I seem to remember when my father was doing hill climbs and sprints in his Mk2 Jaguar there was a friend of his with a Plymouth Barracuda. He could sit on the line with his left foot on the brake and rev the nuts out of the engine then when the light went green he just released the foot brake and away he went. Not so in my S type.

 

The inability to rev when in gear is not something that I've come across, though my experience of automatics is limited. Is it the same in every gear (I don't remember the options on the BW 35)?

Edit: every gear not year 😕

 

Not with the Varamatic. 420's were fine. I would not put 1200psi on the first & second type steering boxes. Max 1000psi on the older boxes & early first type Max 850psi until they changed the top material that used to warp.

 

With an electric pump, you could either find a teenager to design and program a processor that adjusts the pressure with vehicle speed and raises the idle when you steer or you could put a switch on the dashboard to do it. I seem to remember small Fiats with a switch 'city driving' and something else. I don't know if it changed anything, but it entertains the driver.

 

What 's the belt tension like? The spring loaded tensioner on the 3.4/3.8 isn't great and it possible that under load when needing steering assist at low revs the belt is slipping on the pulley. I measured my belt tension and the spring loaded pulley couldn't provide anywhere near the correct amount of tension - from memory it was something like 20% of the typical amount for a belt of that type.

 

I will check the belt tension but I am pretty sure it is tight enough.
Anyone know if there was a smaller diameter pulley for the Generator. I run an alternator inside the old generator body which then powers the PAS pump so a smaller pulley might speed up the pump at low engine revs.
Sorry I seem to have highjacked this thread.

 

I personally would leave it there as it will keep the hood a bit cooler. To really deal with the heat you might review my post here as I had much more of an issue due to the powerful V8 in my saloon, https://www.jaguarforums.com/forum/m...ouvers-191223/

the heat build up if not addressed can affect all types of things from your power steering if you added that, to the ignition, etc. but it can be resolved...

 

jjsandsms,
It has taken a while to dig it but I did find it today. It is a Mark IV Allegro brand / underdash model from the 1970's.
I will update later with pictures. It has 3 speeds and two fans, two front vents, and two side vents. Evaporator is inside the case, Looks simple to me.
I also have the accumulator / dryer, adjustable belt pulley, drain hoses, and miscellaneous hardware and wiring which includes a relay.

 

jjsandsms

here is the unit: The compressor support brackets are the long stick and angled solid bracket shown in the second picture. Third picture shows the idler pulley and accumulator / dryer.

 

Thanks for the photos. The brackets are of interest as I have found there were several different ways to attach the compressor. I have a friend who has a XK120 coupe that had AC added. They used a smaller high output alternator mounted above the compressor which is located where the generator/alternator was located. The smaller alternator is then driven by the compressor with a short belt. Thus no idler pulley is needed.

Thanks the photos are useful.

jjsandsms