Seeking information about AC air flow directions

(Roger Mabry) #1

My great AC shop has been trying to find the source of the abnormal high side vent temp with the AC on… normally I see 39-40F at the side vents with the
AC fans on Low speed…they are about 5 degrees higher when the new GM fans are on High speed. Now they are only producing 53F temps… all else has been confirmed to be working properly… thermostat cycles off/on properly. The pressures on the charging gauges are proper and comparable to past figure.

Nothing appears to be wrong…I am looking for technical information that might have been in a Jag Shop Manual… the air flow direction using inside/outside// that shows air flow and hopefully has some flow speeds?

The '71 S1 XJ is the first year Jag had all the AC stuff inside the car… no rear evaporator etc. and two fans in the firewall.

Is there any information/knowledge of why there is only a thin piece of foam wrapped around the heater matrix/core between it and the coils in the evaporator? I have attached photos of the two with the heater matrix out in one photo and in place in another. Rear of the evaporator is shown to provide information about the coils.
Attached Thumbnails

(Frank Andersen) #2

What about temp at centre vents, Roger - same difference…?

An answer is higher ambient air temps, of course - but the set-up should not change outlet temps with ambient inlet if it is working perfectly…

All air is first passed through the evaporator for cooling and drying, then passed past or through the heater core for tempering. In full cold the heater core is mainly, but not entirely bypassed - and the heater valve is closed; check that the heater valve is closed? The bypass flaps may have changed? The expansion valve may have changed - not necessarily malfunctioning? If the temps are the same side to side, the ‘fault’ if any, is not in the side branches…

The difference is really too small for conclusive fault-finding…?

xj6 85 Sov Europe (UK/NZ)

(Roger Mabry) #3

Frank, stock there are no center vents on a S1, just the two side “fascia” vents… I have added two, the source for one is from the bottom of the evaporator where a hole was already. The other source is from the the right hand tube that used to feed the rear passengers heat and cold. The air is even on both sides and the temps the same 53F after cooling down the air.

The heater functions perfectly… (water flow has been confirmed off by clamping of the feed line) but heat is not needed much in So Cal. AC is used about 300 days per year. They are separate systems on a S1… no climate control blending is done. My questions concerns the closeness of the heater matrix and the coils in the evaporator with only a thin piece of foam being wrapped around the heater coils.

The expansion valve is a new one, setup with R134 - adapted to the S1 flare on the right side and the capillary tube
extended by cutting and adding more tubing to the bulb on the left (drivers) side. It is functioning properly.

I am afraid some of the insulation from the two fans area have dropped down and are blocking the screens around the
coil in the evaporator. Any proper examination involves removal of the center console and maybe much more… I did
this about 10-15 years ago when the heater matrix was leaking. The pictures show how far down the removal is
to take out the evaporator.

I am hoping someone has a S1 Jaguar Shop Service Manual and can look for any information about the PATH of the air that flows through the evaporator. Plus, is there any flow information in amounts that pass through the evaporator in a period of time and how is that measured? The shop says some manufacturers give that info for troubleshooting. Do the manual talk about the heater matrix/AC in any manner? I only have aftermarket manuals and the Jaguar CD parts and service manual. Something has changed recently with no work being done to stop the very cold air of the past and only
allow the air to cool to 53F…38-40F is much better and desirable. The volume of air at any of the vents has not changed.

All we know is the air flows from the top flap, either from the outside of the car or from the inside depending on how it is set. It then enters the evaporator and is pushed around the inside/coils and out the exits that are selected open. With more air speed, the air feels “cooler” on the faces of the occupants… but with the speed the air heats up… Coldest air by measurement is at minimum fan speed… this is normal AC stuff.

The only other suggestion I have had is the Jaguar Ranco thermostat… it does cycle off/on but may be doing this too early and not allowing the maximum amount of coolness to occur. It is possible the capillary tube has backed out of the coils or the thermostat is failing after only 46 years! This will be tested today by the shop…it is easily replaced as it is external to the evaporator and attaches to the front surround panel.

(Colonial 1) #4

Hi Roger,
I have a S1 Repair Operation Manual (albeit for XJ12) which doesn’t offer any information on this. The level of a/c info is about the same as in the XJ6 Service Manual.

(Frank Andersen) #5

The Ranco just disconnects the compressor clutch, Roger, stopping the compressor - which may be supervised…

However, stopping the compressor will drop system pressure, and that there is no problems with pressure - the Ranco is likely innocent,

(Frank Andersen) #6

If your AC is the Delanair I it probably follows the logic of the better documented Delanair II - but lacking the centre vents, the airflow differs. And Jaguar may have chosen a different system initially. The Del II uses the centre vents for max cooling, though also to deliver bended air as the cabin temp reaches the desired temp - the side vents ditto, but their flow can be manually controlled

The slower the air moves the mre ‘cold/heat’ is transferred to the air from the evaporator/heater core respectively - though the effective cooling/heating effect of the cabin increases with airflow, within the capacity of the respective parts. Effective AC systems first cools the air in the evaporator, to dry the air by condensation, then reheating in the heater core - which influences air flow. But it is perfectly possible to have the two air flows coexisting, but in separate streams - it is not clear from your pictures if this is your case; but clarifying this is likely required…

The manuals may or may not elucidate on flow routes and flow rates, but not in relevant detail - the appropriate manual for the AC system fitted is likely more pertinent in your case…?

Questions arising; did you add vents before or after the detection fo the change of air outlet temps? Added venting to the evaporator outlet will increase air flow through it - and increase outlet temps…

xj6 85 Sov Europe |(UK/NZ)

(Roger Mabry) #7

Simon, thanks for checking the Shop Manual. I was hoping for advanced information but understand how little was passed on through the manuals.

Frank, the added vents have been there for years now. The temps from the one hose coming from the bottom area
of the evaporator actually gives colder air temps by about 3-5 degrees F. The S1 AC is totally different from the later units… I had a '74 Jag XJ and hated their attempt at Climate Control. Air flow has been increased for the system by the
use of GM fans… they bolt in the old firewall holes and look almost stock… just much more air flow. Only drawback is the increased noise on High speed… but that is mostly used to clear the windscreen or initially when the car has been closed up outside. The rear package tray “hat” has been blocked off with a plastic bag over it to contain all the air in
the car - no flow through and loss of cold/hot air through the trunk area. I have vent windows and side vents if I want
outside air into the car - plus the center grill intake has been modified to bring in the outside air to the side vents if desired. The Jag evaporator and heater matrix, inside controls for the vents and AC are all that is left from the original Jaguar installation.

I am removing the evaporator this weekend and will then return the car to the shop with it out. We evacuated the coolant yesterday for this chore to begin. This is a VERY involved job on a S1 XJ, they wrapped the car around the heater matrix and evaporator… job is MANY hour long to do the R&R… I removed this one about 10-15 years ago and learned a lot about the inside of a Jaguar! Reason that time was to fix a leaking heater matrix that lives behind the evaporator.

The expansion valve was replaced again, this time with a modern valve and long capillaries - it is equivalent of the stock valve in size but setup for use with R134.If interested, contact me for the shop address and phone number.

More close examination was made and a laser probe used to measure the temp of the floor of the car at the air flow area below the evaporator… the hole used for the second vent tube in this car. The temp, with the car inside the shop and AC running on High speed, 83.5F.

The plan is for me to remove the evaporator and return the car to the shop with it out… examine the whole area behind the unit and then put insulation EVERYWHERE in that area. We need to lower the firewall/floor temp in the
evaporator area and behind the stock Jag vent tubing.

We are hoping that the sudden decrease in side vent temps and the other vents is due to a leak around the evaporator and while doing this, will insulate to get even better temps in the future.

Should this plan fail, I will convert the AC/heat to a Vintage Air system… but that would mean making a new side panel for the center console to cover the end of the AC box that would stick out, losing some glove box area and the under the glove box shelf. Plus, all the engineering needed for the controls to remain stock looking. Hopefully we can find and solve the temp problem using the stock inside stuff. Everything outside - in the engine compartment area was updated years ago when the conversion to a SBC was done.

(Colonial 1) #8

Thanks for posting the details specific to the S1 for future reference.

Wouldn’t it be great if the market for these cars improved enough for a bolt-in replacement from the aftermarket supplier to be developed? I suppose reducing manufacturing costs would be a factor as well.

(Frank Andersen) #9

Blocking the rear shelf ventilation is counterproductive, Roger…

It was designed to allow noiseless venting of cabin air, while still maintaining a degree of overpressure in the cabin - preventing ingress of outside air fumes. Also, cabin will cool faster if the ‘hot’ cabin air is replaced by cold air from the AC instead of relying on convections…

However, like the some alterations you have done; it is not clear which conversions were done immediately prior to the discovery of the side vent temp rise - to possibly explain it…? I assume that there is no change that the earlier lower temp vent reading was ‘the’ spurious reading…?

All that said; the higher vent temps will delay cabin cooling to some little(?) time, but if the system is still able to maintain cabin temp at set levels; system cooling capacity still seems adequate? if so, the rise in temp seems a minor glitch, not requiring drastic action - except for the principle of the thing, of course…:slight_smile:

I’m not familiar with the details of the earliest AC; the plain heater system used a heater sensing unit in the air ducts below the instrument panel to vary heater core flow - I assume a different set-up applies with the AC?

xj6 85 Sov Europe (UK/NZ)

(Roger Mabry) #10

Frank, none of these mods have JUST been done… they have been on the car for years now. Eliminating the flow through ventilation helped keep the car cool or hot… by not letting the air out of the car. US autos of the same era had vent windows and side ventilation vents and the car windows to let out the air not desired.

It is counter productive to try to heat or cool any car with the new air being let out… having a very quiet car was the
Jaguar goal… but not efficient in heating or cooling… guess the temps in the UK are much cooler than the southwest or the inefficient Jaguar S1 XJ AC system would have been improved much earlier.

As other owners know, it would be nice if a AC manufacturer would make a new bolt in system for the evaporator heater with the needed extra vents that was efficient like today’s systems. GM fans are a direct replacement
but the rest of the stuff needs modernizing.

By eliminating all the other outside the cabin AC stuff as sources of the high vent temps, we have gotten the problems source down to the the stuff left inside. Insulation of the evaporator firewall area and the floor underneath can only help cool the air better. The rest of the inside of the car has been totally covered with insulation, including under the headliner and inside the doors… from the area above the pedals to the rear package tray. If you want less noise in a car, add more insulation - plus it helps keep the car cooler by a lot.

By next week the cause of the high vents will show up…my personal opinion is the non adjustable thermostat… by replacing the RANCO brand with a totally adjustable unit… the high and low temps and other controls can be hand
set… I think it is stopping the compressor too soon - at a higher than desired temp… we have sourced another brand
that can replace it and it on the LIST.

But trying to cool the car with 83.5F floor temps in the air path under the evaporator being added to the cooling air is not efficient.

(Roger Mabry) #11

Thanks to David Boger for looking in his Shop Manual for the thermostat specs… as expected the info in the shop manual is not much more complete than the regular service manual on the Jag CD.

Evaporator is out now… no apparent problems noted. Will put insulation on the flooring under the area and around the firewall high up so the vent tubing does not receive any heat from the engine compartment. The rest of the car is already insulated.

The left hand side of the expansion valve currently has the stock pipe with the return hose to the compressor… it will be changed to one with a screw on fitting for ease of servicing the system in the future.

I expect the thermostat will be replaced with another brand that is totally adjustable. That way we can control the start/stop temperature the compressor cycles at in the future.

Removing the S1 evaporator is not a fun job. Took about 6 hours today and parts of the dash wood had already been removed prior to today. Doing the work myself will save me a lot of shop hours of labor. It will be tested with coolant for any leaks… but the system was holding the charge before, so this is only a precautionary testing.

(Frank Andersen) #12

By next week the cause of the high vents will show up…my personal opinion is the non adjustable thermostat… by replacing the RANCO brand with a totally adjustable unit… the high and low temps and other controls can be hand

set… I think it is stopping the compressor too soon - at a higher than desired temp… we have sourced another brand

that can replace it and it on the LIST.

**The purpose of the Ranco is of course to stop the compressor when the temperature of the evaporator drops too 2C - to prevent icing in the system. If it disconnects the compressor at higher temps - it is defective. Or the capillary tube is incorrectly inserted - ‘10 cm in and in contact with evaporator finning’…?

Cannot see an adjustable ‘Ranco’ doing anything better; if it drops evaporator further, you risk icing - and increasing temp is not the intent.

As for venting; if cabin temp is 30C and the evaporator outlet temp is 5C - replacing the hot air by venting is quicker than cooling the stagnant air in the cabin. And vice versa for heating - and a secondary function of the venting is to vent out wet breathed air from the passengers. replacing it with dried air from the evaporator, reducing window misting…

As an aside; there is a chart in the workshop manual (for the Del II) relating high side pressure reading with ambient temps - and the low pressure readings with evaporator temp. Is it something like that for your system - possibly explaining the temp differences you have experienced…?

xj6 85 Sov Europe (UK/NZ)

(Roger Mabry) #13


The manuals on the CD and Shop Manual are very brief for the S1…not much detail for my system. The High and Low pressures in my system are correct (per the shop) for a system of this type… I had a pressure chart but it is attached to the Service Information printed out and left at the shop. They have done LOTS of conversions and have many years of AC experience in all types of vehicles. Ambient temp has been around 85F when all this work have been done… it is still hot in So Cal (except for the last day and next two).

My thoughts on the adjustable thermostat… RANCO not adjustable… it is possible turning off too soon and not removing the maximum heat… even though it is cycling the compressor On/OFF now. That compressor cycling is controlled by the thermostat… correctly or not at the temp it “senses” to be its setting.

Big question now… how much insulation can I really fit into the floor area and get the evaporator back in place?

It is true they wrapped the S1 XJ around the heater matrix and evaporator and all the vent tubing barely fits.

(Derek Bauder) #14

I think this is going to be my winter project this year. I’d rather bite the bullet and replace it with modern equipment than try to get 40yr old English AC to work.

I’m sure I’ll be pinging you for advice (and sympathy…) :slight_smile:

(tony) #15

Hi Roger, have you considered whether it is possible to replace the evaporator itself with a modern universal, or unit from another vehicle?

I believe they are up to 20% more efficient (plate&fin vs serpentine, I think without checking my books)

Long shot maybe, as space and orientatation may be tight/impossible, but every little % helps in the dream of an ice-cold S1 XJ

(Frank Andersen) #16

In principle, Roger, there should be two ‘thermostats’ involved; one relating to cabin temp/air flow temp. On the SI with plain heating, this is the ‘heater sensing unit’ which varies flow through the water flow through the heater core. This ‘thermostat’ is varies vacuum applied to the heater valve and heater flap actuator - basically using ambient air to cool and heater to warm according to driver’s ventilation control settings to automatically control cabin temps…

On the Del II an in-car sensor detects cabin temp and an electronic AC amplifier translate various sensor data to control flaps, heater and fans via a servo. The question on your system is whether such ‘automatic’ controls are used to stabilize cabin temps - and if these are involved in the change of outlet valve temps…?

The Ranco is just a switch, connecting and disconnecting compressor to prevent that the evaporator from freezing up. The main temp control, ‘thermostat’, for maximum cooling effect. of the evaporator is the expansion valve, varying refrigerant flow into the evaporator based on outlet pipe temp and inlet pipe temp - to ensure that the correct amount of refrigerant is injected into the evaporator. All refrigerant must be evaporated, with no liquid residue

This ensures that the evaporator is kept as cold as possible - the maximum cooling effect. If the outlet pipe temp increases, the expansion valve increases refrigerant flow - and vice versa, to ensure the evaporator stays the coldest possible/allowable. All the while; the evaporator is affected by the air flow through it - but if the ambient air temp is too low to keep the evaporator above 2C even with the regulating effect of the expansion valve - the Ranco turns off the compressor.

In effect; the Ranco, working properly, has no influence on actual evaporator temp variation. If the Ranco turns off the compressor prematurely; it is faulty - but even then; the evaporator does not operate continuously at the limit of 2C, it is likely ‘warmer’ than that. Ie, air outlet temps is not necessarily tied to Ranco controls - and the cooling capacity of the evaporator is not infinite. If ambient air is hot enough; even optimum delivery of refrigerant may not prevent its temps to rise. And also; the faster the air is flowing through the evaporator the less the outlet air is cooled - and as the ambient airflow itself always heats the evaporator, the feedback effect will influence outlet air flow temps…

In theory; checking evaporator temps versus air outlet temps is one way to clarify mutual effects. And indeed to verify, by watching compressor engagement/disengagement clarifying if the Ranco is functioning as it should. A somewhat risky test is to bypass the Ranco, to see how this affects air outlet temps. However, this may cause destructive icing and may not be conclusive…

Adding further Insulation around the evaporator (and heater) to reduce outside interference is fair enough - but probably has minimal effects, given the overall system capacity…?

Much depends on the configuration of the various controls on your AC system - to eliminate possible factors other than the ones mentioned…

But again, if the system gives satisfactory cabin temps; drastic actions seems like a bit of overkill…?

xj6 85 Sov Europe (UK/NZ)

(Roger Mabry) #17


Yes, I have been following another Forum member who has converted his S1 to modern AC. It has been
done before this but his AC system comes with new dash wood, adjustable tilt steering column and new styled center console. I only want to convert my system (maybe). Mine has been working fine until very recently 38-40F side vent temps… then the temps raised up to 53F for a reason not found yet.

As Frank has explained each pieces purpose… we have eliminated all the item under the the cause. Removing the evaporator to examine everything was just a step in the process. I will insulate under it all the way to the bottom of heater matrix… the rest of the car is insulated.

Frank, my heater thermostat is non vacuum, it is a Vintage Air Heater Servo unit with its own little control box… all electric. The only vacuum lines left in the radio/heater air are for the center scuttle vent controls. We have confirmed that is not opening unless done by the On/Off switch that is the same one used by Jaguar but with potentiometer control shaft used for the On/Off. The heater water control valve is controlled electrically by that switch.

When the evaporator is back in the car, we will probe the fins when running and confirm the temp the thermostat actually cycles off the compressor… if too early we will change the thermostat. I am just following the shops logical method of determining the cause and confirming nothing has changed inside the over the years.

The photos show the newest expansion valve for R134, it is just like the OEM valve except filled with and setup
for R134, part number 040401 on top of the valve. That pipe on the valve had already been converted to a modern
threaded end for ease of taking off the hose. The other side now has been done the same way. Being able to
easily remove the tubes makes taking out the evaporator and replacing the valve is much easier.

I told them at the beginning I am keeping the car and wanted cold AC air… they are complying and I am doing the
majority of the work since I have the intimate past experiences and Jaguar “skills” to do the job, plus the time. It will
be completed very soon in time for our winter!

(Frank Andersen) #18

It’s all rather odd, Roger - a temp change without an obvious cause, and further item changes not offer any temp changes…hm…

As long as the compressor is running, the evaporator is at maximal cooling - given proper expansion valve function giving optimal delivery of refrigerant. Air vent temps may still vary (as may evaporator temp) depending on changes in ambient temps and air flow speed - which again refers back to the initial question of air flow routing…

Since my experience is with the ‘automatic’ regulation of the Del II, based on cabin temp - a similar symptom may there come from some control failures. In the Del II the system will run full cold until the set cabin temps is reached - then resets to deliver blended air at the desired temp, using the heater core and fan speeds to control cabin temp. My imperfect understanding of the earlier system offers no help here

Since the system has been checked out by competent AC technicians; it’s vain to suggest that the system was improperly evacuated before refill, and the receiver drier not changed. Leading to contamination, which may give proper pressures, but inefficient cooling…

xj6 85 Sov Europe (UK/NZ)

(Roger Mabry) #19


We are still looking for the temp change cause… the expansion valve was replaced this time to use one just found with the proper size and capillary tubes that do not need modification. It did not change anything but made it more “stock” except for the R134 being used internally in the valve bulb.

I am sure this S1 XJ is supposed to work sort of like the Del II, reach the desired cabin temp set on the thermostat and then shut down the compressor… that is not happening now. Max temp is selected and it does not reach that desired temperature… I only have numbers, not temps, but all the way clockwise is coldest temp.

I am sure the tech did the correct job in evacuation and charging of the system…receiver drier was changed due to be opened to atmosphere for valve change.

My guess, is the thermostat is slowly failing and shutting off too soon - at too high a temp… that will be checked first thing after all is back together again. Am waiting for heat insulation material to arrive to start the reinstall.

(Frank Andersen) #20

[quote=“Roger_Mabry, post:19, topic:357814”]
I am sure this S1 XJ is supposed to work sort of like the Del II, reach the desired cabin temp set on the thermostat and then shut down the compressor… that is not happening now. Max temp is selected and it does not reach that desired temperature… I only have numbers, not temps, but all the way clockwise is coldest temp.

In the Del II the compressor runs continuously, Roger - cabin temp is controlled by resetting flaps and fan speeds. In principle diverting a suitable amount of air passed or through the heater core. The compressor is only disconnected if evaporator temps drops below 2C - independent of cabin temps. I don’t know how cabin temps are controlled on the early AC versions, so can’t say what may go wrong here to interfere with max cooling…

Obviously, we don’t really want to drive a car with inside temps constantly at 50F or below - but certainly; high cooling and heating capacity will serve to reach desired temps more quickly, and cope with extreme temps. So your chase is certainly worth while…

xj6 85 Sov Europe (UK/NZ)