Hi Neighbors,

Without real time information you are unfortunately shooting in the dark.

From your description I do not think you have a cooling issue but, maybe.

The fans speed is controlled by the software; it varies the pulse width of the voltage thereby changing the fan speed. That sounds fancy but the bitron switch is telling the computer to change this speed, there is no discreet switch, independent of the computer, which changes the fans speed/voltage.

My xk8 is apart for the next several months, I have a Foxwell Scanner nt-530 loaded with the Jag software, and you are welcome to borrow it for some time. It is pretty powerful and reads most everything and allows resetting many variables. With it you will have a better handle on what is happening in real time.



As an aside, back in the late 90s I had a Ford SHO, they were known for having the compressor run cold then shut off and after a while cool again. The repair was called a shim-ectomyy. I have no idea if this applies but back in the 90s Ford and Jaguar were pretty much tied at the hip and many Ford parts are on/in/around the jags of that time.

Re: A/C Issue - Works Great - Then Blows Warm - Then Blows C

Post by Zenriddles » Thu Jun 24, 2010 12:38 pm

Needed - "Shim-ectomy"

Go here -
http://www.v8sho.com/SHO/ACClutchAdjustment.htm

97 SHO Ebony 190K -Welded



wj

 

Cheap voltmeters are perfect.

Yes, if the relay contacts are dirty, that could cause the problem.

I'll be out for the rest of the evening; have to attend am event downtown.

I will read and respond to your posts late tonight.

hope cleaning the relay works

 

Hi,
The fan behaviour definitely sounds wrong. Their operation is a function of both engine temperature and aircon state.

This is all normal

1. OK
2. May be OK
3. Should only occur if either the engine temp gets too high, or the refrigerant pressure drops below 8 bar
4. OK, but note that the temperature gauge is a placebo. It has three positions: cold, 'normal' and 'oh cr*p' By the time it moves towards the red region, your engine is already too hot. Take engine temps from the OBDII reader.

I've borrowed these two snippets from the AJ26 / AJ27 ENGINE MANAGEMENT SYSTEMS training guide that may clarify the effects of the relationship between engine temps and refrigeration pressures on fan and clutch behaviour:







That's definitely wrong.
The fans run in series at the low speed (i.e. they share the 12V feed), and parallel at high speed (each has a separate 12V feed)

Removing F12 should either stop both fans, or stop the RH fan - depending on which mode the ECM has commanded. Removing F14 should stop the LH fan, but only if the ECM has commanded high speed operation.

There is a fan control relay module located under the LHS front here:
https://www.jaguarforums.com/forum/x...8/#post2014976

Pulling F14 would have no effect in low speed mode, ...but I cannot see how the RH fan is getting power with F12 removed, even if there is a fault in the module.

Are there any signs of work having been done in this area?

 

Today Arthur drove the car to the mechanic. When he arrived he noticed the fans were at full fast blast. To test he started the car again but the fans went to low speed, he left the car running with AC on but the fast fans never engaged and after a few minutes the clutch disengaged.

Just to rule things out, we connected the fans directly to 12v and both fans run at full blast.
With an outside temperature of 104 degrees Fahrenheit, we started the car and let it run with AC on (with the fans direct) for several minutes.
Coolant gauge remain, as always, in the center and the AC clutch never disengaged.

At least we know that when the fans run at full blast the water pump at low RPMs is doing it's job, but we will change the coolant pump and thermostat no mater what.

Some of the times, when the engine coolant temperature and/or the refrigerant pressure raises above it's thresholds, the fans are not receiving 12V.

Is it normal that I didn't see any warnings that both fans were not connected to the car electrics?

Thanks for your input.

 

Hi,

Just an idea... If it was my car, I would check all the ground wire connections and the connectors having to do with the sensors and harnesses they plug into and the relays making sure the contacts in each connector is clean and the connector halves are fully mated. if that doesn't cure things, look for a broken or almost broken wire close to the connectors. Use the "wiggle" method. With the latest behavior of the fans it sounds more like an intermittent situation rather than a complete part failure. Fingers crossed you find the cause.

 

Congrats! Hope the price was reasonable.

 

Hi,

My apologies, I did not see your full post before writing earlier.

I think you are getting a lot closer to solving the problem.

The additional information reduces the search to whatever the coolant sensor high limit and the refrigerant high limit send the signals to and from there back to the fans. I believe you already cleaned the fan relay contacts? Were you able to clean where those contacts go into the base on the car? Oh and the connector to the ECM, ACM (air conditioning control module) By chance did you also check the connectors between the refrigerant sensor & ECM and coolant temperature sensor and ECM? I'll have to look at the schematics to see what else might be the problem maker.

It seems odd there wouldn't be at least a text message of some sort in the odometer window about the fans not connected.

Addendum Sunday morning:

After the car was at the mechanic's shop and the engine at idle speed with the AC on; the fans only ran at low speed. After that, did you happen to drive the car home (or elsewhere) with the engine running at normal RPM and the AC on? Thanks.

 

Someone mentioned using a phone to get coolant temperature. Did this and I've got an accurate real time display of temperature. Can also add more gauges visually to show any data (flow rates, MAF, fuel trims, etc) available at the OPD port. It's easy. Get a wireless bluetooth connector ($7 cheap to $35 and probably no difference). This plugs into the OBD port. Software is cheap. There's "Torque" but I have no direct experience. I went w/ OBD Fusion ($10) because it works on an iPad (bigger display). Real Gauge looks like a great idea but it's more involved to install and only gives temperature. It certainly looks better! Given the engine's sensitivity to heat, can't imagine driving w/o a real number.

 

Check the obvious and easiest first. After all the car was in a garage out in the country for several years. Rodents love plastic covered wiring.

We will check all ground wires and disconnect and reconnect all relays. I may replace all the fuses. Is easy.

Thanks

 

Hi,

Yes, do the easy and inexpensive things first.

Did you happen to drive Wilson home from the mechanic's shop yesterday? With the AC on? If so did you notice the speed of the fans?

I've attached pdf files of the schematics (4.1 and 4.2) with some notes.

Thanks.

 

Both fuses are in play in high-speed mode. F12 powers the RH fan, F14 the LH fan.

I'm a tad confused Earlier, you mention that the fans run at one speed, here it's both?

Yes - there is no direct monitoring of whether the fans are operational or not.

That is what the fan switching (via the fan control relay module) does when the ECM commands high-speed operation. I can't reconcile the wiring in JTIS to the results you are experiencing. Removing F12 should render the RH fan inoperative irrespective of the mode commanded. Removing F14 should disable the LH fan, but only in high-speed mode.

That aside, it appears that you do have dual-speed fan operation? so I'd focus on the AC switching off. Again, you can't make a judgement on engine temps from the dash idiot gauge. A cheap ELM327 clone and a smartphone will give you a much more accurate indication.

Do the pressures in the AC circuit resemble those in the table above?

Finally, on the the '97MY, the AC module additionally monitors the lock status of the compressor clutch. Check that connection is still good. The connector is somewhere around the dipstick retaining bracket. Sorry I can't be more precise on its location.

Quick Q: - what are the last six digits of your VIN? The reason I ask is that it's noted in JTIS that pinouts may not match the diagrams on early cars

 

The car was to be connected to a computer, but fortunately there was another similar Jaguar at the shop and we swap sensors and relays.

Swap the fan relay only, same problems.
Swap the AC pressure sensor only, fans high speed kind of engaged but it was not at full speed, difficult to explain.
Swap both the AC pressure switch and the Fan relay and the high speed engaged as it supposed to.
When we finally tested both transplanted parts it was late in the afternoon and the temperature was "nice", tomorrow we will run more test.

Is it normal for two system related parts to fail? Since the car was living in the Hill Country there was never traffic and the car was always on the move, the previous owner never experience any problems since she only used the car during the nice cooler weather.

This are the part numbers I need to replace. I google them and could not find hits. Who do you buy Jaguar parts from?

LJA7658AA Sensor, and
(?)JA6702AA Relay



I'm getting there

Thanks

 

Progress

Parts swopping on a Jaguar can get very expensive very quickly, so being able to borrow was a lucky break! It's entirely possible that the items failed separately, but weren't noticed by the PO.

The pressure switch LJA7658AA is now LJA7658AB and showing as available from Heritage, so you could get one via a dealership. The relay module LJA6702AA is also listed, but out of stock. Both Jagbits and SNG Barratt list it but they're expensive.

Neither seem to be frequent failures, so consider sourcing from a breaker. Both are common to the XJ8 so will be easier to find.

 

Hi to all. Arthur purchase the sensors and relay from the local dealer. But we have another problem.
Remember the oil leak? Is the left cam cover is broken and needs to be replaced.
Where can I find a new one? Any suggestions everywhere I look are no longer available or out of order.

Thanks

 

I found this cover on line, part number XW936P052BF.
Will this part work for my 97 XK8?
My broken part is XW936P052AC
But since mine is leaking could it be a replacement or a different cover?
I read in the forum some Lincoln parts are interchangeable.
Is there a Lincoln cover that would work?





Your suggestions will be appreciate it

 

OK I'm laughing. Just called JagHeaven to see if I could help out. He got your email. Price is 225. Hey forum, are broken covers often a problem on a 4.0? How about w/ the 4.2?

 

You will need a cover off a 97 or 98 xj8 or xk8 N/A engine. It can also come from a 99 and newer xjr or xkr with the supercharged engine, including the 4.2L. You need one that doesn't have the hole for the VVT. If you can't find one send me a PM, I have a used set off a 98 xj8.

 

Yes I'm in contact with them very nice people.

Thanks

 

Thanks, I just commit to another set. Should have check the forum before.

 

It took forever to get the cam cover. but while waiting Arthur took pictures of the chain lifters and as described by the previous owner they were replaced with modern metal units.



Out with the old bent/cracked cover and in with the new. Plastic, really? I have stronger bakeware in my kitchen! Is the cam cover oven safe?



We also changed the thermostat and the coolant pump, which has metal impellers, should we asume is not the original?

So far no burned oil smell.