DELANAIR AIRCON rotary BLEND FLAPS bit of heat leakage

1989 XJ40 3.6L 130K miles garaged car June 22 2020… that straight 6 engine winds out nice to 5.5K.
MY AC compressor is not working and belt is off pulley. So just fresh air available for now.

I now get only fresh air out the vents mostly from center vent in summer, that all works , nice volume of air blows out center vent but sometimes or most times … the air is warmer than ambient meaning some outside air is leaking past the heater core and out thru the center vent.
Q1_Does this indicate maybe upper blend flap feedback POTENTIOMETER-resistor needs adjustment? or is it normal to have a bit of air leak past the FLAPS through as the core?

Even with a vacuum heater water valve (fairly new replacement part) , car eventually warms up and then park-stop somewhere–car sits—… the vacuum bleeds off and the valve opens up (default with no vacuum on valve is heater valve is OPEN) and thermal siphoning would certainly eventually heat the core up… default valve should have been CLOSED with no vacuum but alas it is not that way.

It is a shame considering the complexity of the system that the AIRCON designers who have probably zero experience repairing anything, did not think to install a PLEXI port or removable plug (called a witness hole in construction industry regarding coupling nuts) inspection hole to see what those “invisible” rotary blend flaps are doing and where they come to rest.
Q2__Is it possible that this is normal blend flap clearance leakage or are those Blend flaps fairly air tight?
Q_3 Anyone try adjusting the feedback POTS?
Yes AC would be nice, our SD509 (no thermal or HI-LOW switch on this original OEM com) comp seized due to low charge, SH7H15 , almost same CC’s displacement, and has same mounting bracket dims and should be a good reasonable cost replacement-just need to pick one of 40 or so back CAPS… thinking GM style 7/8 & 3/4 screw on fittings…
Thanks to all on the AIROCN BradK 1989 XJ6 black and grey

Download this, it will tell you everything about the design and operation of your climate control system …

How I wish that were true, I have that manual and it’s the first thing I looked at. There is nothing in that: “DEALER TRAINING, Delanair MkIV Air Conditioning System” 6meg PDF regarding:

Vent position alignment and and setup

Vent tolerances for air leakage

Troubleshooting guidelines

Voltage guidelines on motors

Zip zip zip zip…No information on the above. “Dealer Training” is at best, enables locating all system parts and reassembling without anything breaking at worst just a overview and not a repair service manual.

This manual is a generalists guide to “principles” - theory of operation, a big difference from a service manual. With a proper service manual one would have Theory and Principles of operation but so much more that would enable rebuilding the whole system to factory specs, and this overview guide hardly qualifies.

I’m sure if there were a misaligned or leaking flap vent Jaguar repair department would spend less time, have a more guaranteed outcome, by swapping out the unit as the manual tells nothing on these alignment and calibration issues.

Tech writing and service manuals have all but disappeared. Years ago Tektronix, Hewlett Packard, even Heathkit made great manuals that you could with time rebuild the whole unit, align and calibrate it, troubleshoot most failures, had good flow charts too everything required to keep the item operational and to factory specs. Amazing manuals, sadly is a dead art. If the above companies owned Delanair, they’d have not turned out such a light weight overview document. That Delanair manual is lacking in so many areas.

Yes it is better than nothing but frankly it is almost nothing.

Thanks for the thought and help, but need more technical information than the Delanair “Overview”

The XJ40 is known as a ‘hot car’ when the A/C is not working.
With or without a coolant cut-off valve (my '91 didn’t have one), in heating mode all of the ambient air gets pushed through the evaporator before, as you would expect, passing through the heater matrix and out of the upper and lower vents.
The problem is that in cooling mode, after the ambient air has passed through the evaporator it then passes across the face of the heater matrix befor exiting the floor and centre vents so it picks up some heat in that process.
Obviously the situation is much worse if the A/C compressor is missing or not working since the ambient air does not get cooled passing through the evaporator but still gets heated passing over the heater matrix before entering the cabin.
Buried in the archives somewhere there is a post from me on that subject when I had to remove the drive belt from the A/C compressoir after it seized at the start of a long journey with no A/C in a car that became unbearably hot even in our UK moderate temperatures.

If you want to check voltages etc, have you a copy of the JDHT CD-Rom JHM1130?
If so there is an excellent diagram of the electrical circuits in a 1990 model which I presume HVAC wise is similar if not the same as your '89 in that it details the voltage inputs/outputs to/from the climate control microprocessor for the servo motors and feed-back potentiometers for the blend flaps.

Bryan Thanks so much.
I have paper edition foldouts electrical schematics… so that’s OK
I was just wondering if anyone fiddled with the POSITION feedback pots… it has on some occasions given cool air, matching ambient temps, but most times yes it picks up heat… maybe the rotary flaps feedback circuit needs its connectors cleaned and pots wipers cleaned, (in audio, pots wipers get dirty and can loose connectivity-a very likely scenario) … maybe the feedback pot is loose (dubious)… I should probably source a BARBED BALL VALVE to just shut off 100% the HW flow in summer and sadly just have to remember to turn it on in winter… but that would put it to rest for sure…

Thanks again for your insight… but sad the OVERVIEW was not a service manual and if it was meant to be one it is piss poor on tech info.

Thanks again
I think if users like you and I designed the system, it would be far superior.

Yes my biggest dilemma is picking the right end cap for a new Sanden SD7H15 compressor to replace the SD509 unit. But it’s a joyous car to drive even without AC.

Brad K
89 2 tone XJ6 NY

My 1990 XJ6 has no vacuum heater water valve so to increase AC efficiency in summer months I clamp off the heater hose with a plastic clamping pliers used in auto repair shops.

1 Like

Good simple idea that works for a flawed complex system

Good idea… plastic clamping mechanics pliers… will look for a nice pair…
Thanks again!

Brad K
89 XJ6 black and gray

Brad …

You stated … “I now get only fresh air out the vents mostly from center vent in summer, that all works , nice volume of air blows out center vent but sometimes or most times … the air is warmer than ambient meaning some outside air is leaking past the heater core and out thru the center vent.”

Not exactly sure what you mean but going back to basics. ALL of the air that comes out of the many vents (demister, facia, both center and ends, floor, and rear) is supplied solely by the two fan assemblies. Each fan assembly has a vacuum operated door on the top which when closed sucks in the air from the cabin and when open sucks in air from the outside under the scuttle.

Since your compressor isn’t working only cabin or outside temperature air (or a combination of the two) is being delivered to the vents. As you know your 89 model has a vacuum operated water shutoff valve that is held closed by vacuum when full cold A/C is selected and then modulated according to warmer temperatures selected. Why is the valve held closed with vacuum and fails to the open position? … My only guess that this is a safety feature so that if it should fail (loss of vacuum) during very very cold outside temperatures it would still provide hot water to the heater core and keep you from freezing to death during your Siberian rally.

So in your case if you keep the hot water from going through the heater core it makes NO difference what position the two blend door are in as far as the temperature coming out of the vents. The doors will merely determine WHERE the air is coming out into the cabin.

Even if you clamp shut the hose feeding the hot water into the heater matrix you will still be getting some warm water into the core through the outlet hose because of heat convection. I’ve actually heard of people putting a water valve on both the inlet and outlet hoses to prevent this.

So in your case if you keep the hot water from going through the heater core it makes NO difference what position the two blend door are in as far as the temperature coming out of the vents. The doors will merely determine WHERE the air is coming out into the cabin.

There is a concecpt called THERMO SIPHONING. Run the car to operating temps. Park somewhere for shopping etc… Water vacuum valve slowly loses vacuum and opens… Thermo siphoning will easily replace the cabin heater core with hot water… Get back in the car after shopping, now CORE IS HOT, if any leakage in the flaps…it will affect the outlet temps…

In electronics and audio work I’ve done. POTS change value and can even loose connectivity due to wipers normal wear action as dirt oxides accumulate on the wiper… if this has happened the final position of the rotary vanes wont be accurate and repeatable with any accuracy. Cleaning the pots (assuming the have not repositioned themselves due to loosening of the fasteners, would make them precision feedback senders again. My suspicion is the POTS could use a clean as any old POT benefits from cleaning.
It can be only 3 things, !-Some heat leakage is normal to the design or this Aircon OR 2 the flaps due to normal seal wear or alignment errors allow air to bypass their seals OR the feedback circuit does not return the same OHM value causing FLAPS to miss the optimal position.

It is a minor heat leak… annoying… I will in the interim get some HarborFreight Hose clamps (set of 4 under $8) and clamp the line or clamp 2 lines… although thermo siphoning could still take place on the cabins heater cores return hose as was mentioned. Since we cant easily check FLAP alignment we experiment with a clamp or clamps.

Thanks again
Brad K

Brad …

As far as your water valve slowly losing vacuum and opening during extended stops why not simply install a $5 one way check valve in the vacuum hose just prior to the water valve. This should hold the vacuum indefinitely…

As I understand it Thermosyphoning relies generally on a free flowing, vertical system to operate. So if you can keep the water valve closed there is no free flow through the heater core which is basically a horizontal system anyway. Although you will get a small bit of static convection water heating from the outlet pipe back into the core I certainly don’t think it will be enough to significantly fill the core with hotter water than is already there.

Hope you can get the entire climate control system up and running soon.

No matter what “tittle” we label the heat transfer concept The facts are the heater core gets heat in the summer … Ive installed a HFreight #65116 $8 clamp set (1inch one was AOK) on the non vacuum valved hose, what may be the return line. I’m sure much less heat will be able to get into the core with a clamp one one line and vacuum valve on other… Will post results as the weather is hot now to see if we have ambient outdoor temps coming form the AIRCON…

Brad K