Curious AC Symptoms
 

So I know that I have no A/C because the air never gets cold. I know that there 's no freon because when I take the caps off the fill adaptors and press on the Snyder valves, nothing comes out. I think also that my thermal valve is burnt. Now the weird part. The compressor clutch is turning on and off as I engage and disengage the a/c system. There's no noise when the a/c is engaged. Sounds completely normal. I can physically see the compressor clutch whizzing round when the Climate control switch is turned on and stopping when I turn it off. So the compressor seems to be working. But there can't be any freon in the system because I would have heard something when I pressed the pin in the Snyder valves. (I tried both and nothing).

I am wondering whether that Thermal Fuse is actually burned up. Maybe just on its way. Theory: I bought it from an old lady who didn't drive it much and I live in New England. Perhaps it was juts out of freon and it hasn't had the AC on in so long that Fuse hadn't burnt up. Surely if the AC compressor was spinning for any length of time with no Freon the thermal valve would be toast. Maybe I am toasting it myself as I drive around with the AC on and no Freon. Just so happens I took a picture of the Thermal Fuse when I first bought the car. Very hard to see if the photo is relevant because the picture was taken from an angle that doesn't capture the areas that now appear burnt. Here's what it looks like now:

https://cimg4.ibsrv.net/gimg/www.jag...c83475c3d.jpeg

https://cimg5.ibsrv.net/gimg/www.jag...edc2bf6b5.jpeg


And what it looked like when I bought it.

https://cimg7.ibsrv.net/gimg/www.jag...6da6401610.jpg

Any thoughts? If my theory is correct, I should not run the AC any more. Alabasi suggested in another thread to just put new adaptors on the compressor feed lines, new O-Rings on the compressor and then fill it with R134.

If my theory is right, then this AC system has not been gone for very long. Maybe a recharge is all it needs?

Thoughts and advice?

if the compressor is clicking, you need to watch it with engine running to see if the cluttch slows down on rotation when it engages with the magnet.

if it does, it might just need refrigerant but also It might need refrigerant oil.

if the thermal fuse is melted, replace it.

you can disconnect the compressor by pulling the electrical connector connected between the clutch and the magnet. That way you can bring air into the cabin by putting the controls in AUTO and 65.

If you don't know the type of refrigerant and refrigerant oil that was in the system you should take the car to a shop that has a refrigerant tester.

in other words, you cannot mix R12 and R134 refrigerants and each requires a different oil. Some people used to recharge with R22 or other regrigerants. Best to confirm with a professional.

Hi Jose

I'm not sure how you answer helps. I've read and re-read what you wrote. You talk about knowing what kind of Freon but I wrote that this has the old style connectors which means necessarily that it had R12 because you can't put R134a into those connectors. Isn't this so? I already know not to mix. I was thinking after I replace the the connectors with r134a, O-Ring seals and flush the system and add a new drier. RIght now I am just trying to determine whether my compressor is functional and I think it is. I am trying to rule in or out non-functionality as a result of low freon (which I know there isn't any).

Also, I have confirmed that the compressor engages when the ac switch is turned on. I haven't jumped it to hear a click because I can see it engage when the ac is switched on. Further it doesn't come on at all when the thermal fuse is removed. I think this means that the compressor is working properly AND that the thermal fuse is NOT blown despite it's appearance.

I uploaded a video of what the ac clutch does with the thermal fuse in place and the ac is switched on.
What you told me seems to be general advice about ac troubleshooting and I have a specific question. I am not knocking you, just asking because you have confused me. Should an engaged compressor run at different speeds? I didn't think so.

If the clutch engages the thermal fuse is good. An engaged clutch does not confirm that the compressor is fully functional. It can be spinning like crazy and not doing its job

If the system lacks freon the thermal fuse should blow. That's the whole idea of the protection system. But....the superheat switch at the back of the compressor might be faulty, or disconnected, or the connection rusty/corroded, thus rendering it inoperative.

The compressor, when engaged, runs at whatever speed the drive belt dictates. That is, there's no 'variable' speed aspect to it relative to compressing freon.

Cheers
DD

I'll add that the superheat switch is normally open. When closed (due to lack of freon) it completes a ground circuit to the fuse, thus blowing it.

Cheers
DD

Hi Doug

I am trying desperately to write clearly and I think I am failing. The Thermal Fuse, AND the circuit as a whole appear to be functional. When the Thermal Fuse is in place, the Compressor works as one would expect. That is to say, 1) thermal fuse in place -> 2) AC Mode Control Switch turned on -> Compressor spins as shown in the video, 3) When AC Mode Control Switch turned OFF -> Compressor doesn't turn.

On the other hand, when the Thermal Fuse is pulled out completely, the AC Compressor does not engage no matter what you do with the AC Mode Control Switch.

Now, it is possible is it not, that the AC is out of freon, but the system has not run long enough (because I live in a place where it is very easy to drive for a while with no climate control on because it isn't that warm or cold and because the car hasn't been in use that much at all) to heat the Thermal fuse up enough to blow it. That is what I am trying to figure out.

As a corollary, I know there is no R12 in it because none escapes when the fill valve is actuated. There's no noise from the AC Compressor. Sounds completely normal. So, assuming the circuit to activate it is good (there couldn't be corrosion where you suggest because then it wouldn't come on or off with changes to the Thermal Fuse- do you agree?) What else could be wrong with the compressor if it Turns on and off properly, doesn't exhibit signs of failure like noise or obvious damage. Doesn't it just leave seals?

@ muttony
Since you say that there is no refrigerant in the system, one of the ways you can check if the compressor is working,( you already know that the AC clutch is activating) is to remove the lines at the rear of the compressor. With the key on and the AC switch on turn by hand or with the engine running you should hear the suction and pressure side doing its thing, you can put your finger on the pressure side and its like feeling for compression at a spark plug hole. The bigger line is your suction or low pressure side.
Normally, when the AC clutch engages, it actually turns the compressor pistons. With the AC clutch disengaged, the pulley just freewheels.
If you are going to switch to R134a, there are a few things you must do.
1. Drain the compressor oil. ( on my A6 compressor, there is a drain plug on the underside of the compressor)
2. Replace the black O-rings with green ones.
3. Replace the dryer and use AC flush to flush out your condenser.
4. Replace the oil with 4 ozs of PAG oil .
5. For best performance with R134a, you will have to remove the expansion valve(NAPA) and replace it with one that is compatible with R134a or use an Allen key and adjust your existing expansion valve (1/2 turn in).
6. Install R134a Adapters on the R12 Schraeder Valve, Remove the schraeder valve from the R12 fitting. The R134a adapters will have its own schraeder valve
7. Evacuate and charge the system 75% of the R12 volume

Thanks. This is what I am thinking of doing. But I am trying to avoid charging the system if I have a compressor problem because independent ac shops are not plentiful in New England. I don't recall ever seeing one. Midas etc, but don't want to do that because they are likely to either refuse to do it or break something.

Good tip about checking the compression.

Oh and Schrader not snyder.lol

So far so good !

What's in question isn't the circuit to engage the compressor clutch. It's obviously working.

What's in question is whether or not the protection circuit....designed to disengage the compressor....is working. It sounds like it isn't.



I dunno, specifically, how long it should take for the protection circuit to recognize that there is no freon. I would think it would happen rather quickly.


I don;t think we have to assume. The compressor does engage so the engagement circuit is good.

I was thinking of corrosion (or other fault) at the superheat switch, which could prevent the protection circuit from operating....but would have no bearing on the engagement circuit


Seals, yes. Or pistons worn such that no compressing is taking place

Cheers
DD

A lot of shops assume there must be something exotic about the AC on these old Jags. As far as the refrigeration side of the system goes, well, it's plain as mud. Nothing remotely unusual about it.

Now, the 'automatic climate control' side of things....that's another story :)

Cheers
DD

Thanks Doug, now I understand what you are saying about the superheat switch. Is there a way to test the superheat switch on the compressor? I thought the Thermal Fuse and the superheat switch were the same thing.

There's a technical bulletin (Service Bulletin 03/84) that says the Thermal Fuse Melt times.

The Thermal Fuse melts at 157-182 degrees Celsius

It takes 2 minutes for the Fuse to melt at 14 v and 5.5 minutes at 11.5 volts.

The heater resistance is 8 - 10 ohms when cold.

See Page 25 of 44 at https://www.terrysjag.com/XJS%203.6%...ash%20Wipe.pdf

I know I have run the AC for more than 6 minutes so I think Doug is onto something here.

More info. I checked the thermal fuse connector (where the fuse plugs in) and the center plug did have some corrosion. I cleaned it off and plugged in and ran the car for 6 minutes with the AC on. That fuse heated up a lot but did not blow. I couldn't touch it at first. I peeled back the bubble of melted plastic so I could see the fuse material itself and it looks good and not burned. But that compressor kept going for 6 minutes. It might go out after more time or not. Don't know. Maybe I'll try it if I conclude I need a new compressor anyway.

I think I have to pull this compressor and check out whether it still works. I wonder whether it might be less bother to just buy a new one with HSLP and delete the thermal fuse all together. I'd be starting with a clean slate at that point. I found instructions on how to switch from Superheat to HSLP on https://www.terrysjag.com/XJS%203.6%...e%20Clutch.pdf at p. 18. The instructions presume you are using a Jaguar provided replacement kit which of course I wouldn't be since one presumably can't get them anymore. The instructions, less illustrations, in case Terrys takes down the page some day.

Modification Procedure
1) Disconnect battery
2) Depressurise the air conditioning system Part No. JLM 1041 JLM 1042 JLM 1043 AEU 1689 DAC 4651
3) Remove the compressor unit, and discard the thermal fuse, bracket and harness.
4)- Place the compressor in a vice as shown in Fig. l and grip using the forward mounting flange. Do not overtighten. As direct metal to metal contact can result in damage to the clutch drive, place a piece of wood (Fig.l A) in the vice on which to rest the clutch drive. IMPORTANT: THE COMPRESSOR MUST BE POSITIONED IN THE VICE AS SHOWN IN FIG.l TO PREVENT LOSS OF REFRIGERANT OIL WHEN THE REAR HEAD IS REMOVED.
5) Release and remove the compressor rear head securing nuts 4 off (Fig.2 B).
6) Displace and remove the compressor rear head (Fig.2 C) and carefully remove filter assembly from rear head (Fig.2 D) and retain. Discard head.
7) Remove and discard rear head 'O' ring seal from main body of compressor (Fig.2 E).
8) Clean filter (Fig.2 D) and compressor seal face. NOTE: BEFORE FITTING NEW 1 0 1 RING SEALS LIGHTLY COAT WITH SUITABLE 525 VISCOSITY REFRIGERANT OIL.
9) Fit and align new rear head seal (Fig.2 E) to compressor body.
10) Fit filter (Fig. 2 D) into new rear head and align head to compressor. Tap rear head lightly until flush with compressor body . Fit and tighten securing nuts to 34 Nm (25 lbs ft).
11) Fit and secure new pressure relief valve (Fig.2 F) to rear head, and tighten to 13.5 to 19 Nm max (10-14 lbs ft max). NOTE: The relief valve is supplied complete with the 'O' ring assembled. Lightly smear with 525 viscosity oil before fitting to rear head.
12) Fit the high side low pressure switch 'O' ring (Fig.2 G) supplied in the HSLP kit to the recess in the rear head location.
13) Carefully locate the HSLP switch (Fig.2 H) and push until it is correctly seated into the rear head location.
14) Fit circlip (Fig.2 J) and ensure it is fully located into the rear head.
15) Fit new 'O' rings to rear head high side and low pressure ports (Fig.Z K).
16) Refit compressor to vehicle and fit new harness supplied in kit.
17) Reconnect battery.
18) Connect and secure refrigerant hoses to compressor, evacuate and recharge system and check operation.

High Side Pressure Switch is Part Number JLM 1043 or JLM 1165 one on Ebay for $35.00. Welsh Enterprises with some wiring for 55.95. 1165 is more plentiful than 1043.

Presumably if you buy a new A6 with HSLP connection you'll have to figure in the cost of the HSLP switch as well. In my case it looks like my Superheat switch might be broken so I can't switch it.

Making Notes for myself at this point.

*Some A6 compressor use metric fasteners; some use SAE. Check before you struggle. No fun trying to thread a metric bolt into an SAE hole.
*Compressors with the HSLP switch don't use the thermal fuse. The switch at the back of the compressor has a wire that goes right to ground.
* This post has an instructional pdf on how to convert from Superheat to HSLP.
*The connection at the compressor clutch is 2-wire regardless of superheat type or HSLP type. There is a 1-wire connection at the rear of the compressor for the HSLP or superheat switch. The linked post also contains a pdf with instructions for wiring HSLP.
*Post with Pictures of the different connection holes for HSLP and Superheat.

Cheap new A6 are supposedly available, but I haven't found anyone. If someone coming across my notes knows of these please reply so I can look into it. I can find plenty of Reman'd ones. Also, I have a P/N for the HSLP Switch and harness that would have to be purchased, but they cost a bit. I think a GM version is surely available, But not P/Ns for the American versions.

Try not to run the compressor too much with no refrigerant.
If you go to Walmart you can buy the cheap R134 refrigerant. Down here in Florida it's like $5 per can.

@Doug I fiddled a bit with the compressor when I got home from work today. I confirmed that the clutch engages with 12v by jumping it. I didn't hear the noise when it engaged as some said I would , so I thought maybe something else was up. But when I jumped it I heard a little clack as it engaged. I think the clutch is very close to the engagement point (meaning the gap is very small) when it isn't engaged. It made a little "click" when it engaged, You wouldn't hear it even over the wind noise if it was outside. Is this significant to failure of the superheat switch to work?

More importantly, I checked the superheat switch fuse for continuity and it is still good. This is so even though it clearly melted the plastic. In the second picture above you can see the melt, and when I tested the fuse it got very hot but didn't fail.

I pulled the superheat fuse connector off the back of the compressor and there is no corrosion that I can see. The connector's metal is bright metal. A little dirty, but I've seen much worse. With an inspection mirror I could just see the connector pin for the actual switch and it looked like bright metal too. I felt it and didn't feel any corrosion; it was very smooth. Any chance the switch part in the compressor (that I can't see) is somehow broken inside of the compressor or internal to the switch?

Or maybe it takes longer than 6 minutes to fail? I'm trying to think of how long I have run the climate control since I owned it. Can the fuse be the wrong one? Do they make more than one kind of these fuses? Something with more resistance?

Looks like I was correct about the delay for the Thermal Fuse to blow. Theory - My Thermal Fuse is no longer attached to the compressor but is out in the open zip tied over the front fender next to the coolant expansion tank. Is it possible that in this location air passing through this location keeps the fuse cool (air cooling?) delaying the fuse blowing?

More info on the Thermal Fuse:

Kaps on https://www.autoacforum.com/i/ratingicons/note.gifSun February 06, 2005 7:59 AM https://www.autoacforum.com/i/dominant/trans.gifhttps://www.autoacforum.com/i/icons/toolbar_offline.gifhttps://www.autoacforum.com/i/dominant/trans.gifhttps://www.autoacforum.com/i/icons/toolbar_view.gifhttps://www.autoacforum.com/i/dominant/trans.gifhttps://www.autoacforum.com/i/dominant/block.gif

Dear Alex,
Does this Jag have separate Thermostatic eXpansion Valve (TXV) and Suction Throttling Valve (STV), or a combination Valve In Receiver (VIR) system?

A superheat switch works like this-normally open, closing at approx minus 1-5 PSI, which causes a short to a slow acting (the resistor) fuse, normally with three terminals. The slow acting feature allows the fuse to withstand momentary surges of current(caused by momentary closing of the switch) without opening the circuit. A standard fuse, which opens immediately when shorted, will not allow for temporary fluctuations which can be normal under certain conditions.

The superheat switch senses compressor return (suction, low side) pressure through the large hole in the center of the switch port. The switch/fuse circuit is designed to prevent compressor failure when the refrigerant and oil return is low. This less than 0 pressure can be caused by low refrigerant, or by a stuck closed Suction Throttling Valve(STV). The STV, depending on manufacturer, is often called a Pilot Operated Absolute valve (POA) because the actuator is controlled by a pilot mechanism unaffected by barometric pressure.

The superheat switch/fuse system originated on GM vehicles in the early 1970s, to prevent compressor failure when
1)the thermostatic expansion valve or POA valve sticks closed, starving the compressor's moving parts of lubrication
2)low refrigerant due to a leak causes oil starvation.
The addition of this safety circuit substantially reduced the frequency of compressor replacement.

It is necessary to remove the 3 prong thermal limiter switch and jumper the circuit during system charging, till lower than normal suction side pressures are raised by a full charge.

To test the x valve and POA valve operation:
If the system has 2 ports on the low side, one will sense evaporator pressure, the other senses pressure after the suction throttling POA valve. Connect gauges to both.

remove Thermal limiter switch, jumper circuit, run engine and AC system, system pressures should be normal.
disconnect blower motor, raise engine RPM to 1000-1500, watch evaporator pressure gauge, it should cycle between 25-32 PSI. Compressor return pressure will cycle between 0-32 PSI, it should not go below 0 PSI. You will see the STV cycling when the compressor return pressure goes up and down. If return pressure goes below the range of minus 1 to minus 5, TXV or POA is defective. Don't do this for more than 5 minutes, to prevent compressor damage.
I hope this helps.
Kaps



-------------------------
A. C. Doyle said "Eliminate all other factors, and the one which remains must be the truth."

George Bray on https://www.autoacforum.com/i/ratingicons/note.gifSun February 06, 2005 2:17 PM https://www.autoacforum.com/i/dominant/trans.gifhttps://www.autoacforum.com/i/icons/toolbar_offline.gifhttps://www.autoacforum.com/i/dominant/trans.gifhttps://www.autoacforum.com/i/dominant/block.gif

The XJ-S / A-6 compressor superheat switch is normally open. It closes when suction pressure drops to an unacceptable level (negative pressure I believe), or it could be when temperature increases to an unacceptable level. Iâ € ™m not certain. Anyway, closure of the switch completes a circuit to earth, causing the thermal fuse to blow after a delay of around 2-5 minutes. The delay is enabled by a resistor acting as a heater in the 3-terminal fuse box assembly.

The objective when the thermal fuse blows is to stop the compressor, semi-permanently, until a service engineer rectifies the underlying problem, as Jaguar would envisage. No allowing for DIY!

Low pressure may occur for reasons such as a low charge of refrigerant or possibly a blockage, e.g. of the expansion valve. Yes, the XJ-S has an expansion valve. Iâ € ™m 99% certain there is no suction throttling valve (STV), or combination valve in receiver (VIR).

My suggestion is to leave the superheat switch disconnected, by-pass any fuse and fit a HPCO switch instead.

Jaguar recommend the following checks â € œif the refrigerant level is satisfactory and there is not a blockage in the air conditioning system but the thermal fuse persists in melting:â € �
â € œTEST PROCEDURE A
For use with a cold engine and at ambient temps below 30C.
Connect a test lamp in series with the superheat switch. Note: with the test lamp connected in the circuit, it will prevent the thermal fuse from operating as a safety device, therefore great care must be taken when carrying out the test.
Connect a manifold gauge set to the air con system.
Ensure a serviceable thermal fuse is fitted.
With the ignition and air con switched on.
Depressurize and evacuate the air con system, then close the manifold hand valves.
The test lamp should not light during this operation.

It the test lamp lamp does not light then follow test procedure B.

TEST PROCEDURE B
With test lamp not illuminated, connect the centre hose of the manifold gauge set to a refrigerant supply container.
Start and run the engine at about 2000 rpm. After a few minutes the lamp should light. As soon as the test lamp lights, carefully operate the low pressure hand valve to allow refrigerant to charge the system. As soon as the system becomes charged the lamp should go out.
If the above lamp functions do not occur, renew the superheat switch.
After checking, remove the test lamp from the circuit and reconnect the switch lead onto the terminal.â € �

The Jaguar manual also says:
â € œOn â € ˜earlyâ € ™ vehicles (and this is written in a manual published c. 1989/90), a superheat switch is included in the compressor clutch circuit to provide a compressor protection system. The superheat switch and thermal fuse guards against a low refrigerant charge or blockages causing extreme superheated refrigerant vapour conditions resulting in compressor damage. The thermal fuse is a sealed unit containing a heater and a meltable fuse. The superheat switch is located in the rear of the compressor in contact with the suction side refrigerant vapour. With a low refrigerant charge or a blockage, the pressure drops and the temperature rises. This condition closes the superheat switch contacts which complete the circuit, melts the fuse, and disconnects the battery supply to the compressor clutch winding and the thermal fuse heater. The compressor ceases to operate and damage from insufficient lubrication will be avoided.
The thermal fuse melts at 157 to 182C
Time taken: 2 mins - 14v system voltage
Or 5.5 mins - 11.5 system voltage
The heater resistance, cold 8 to 10 ohms.
CAUTION: After a thermal fuse melt, establish and rectify the cause before replacing the thermal fuse unit complete.

High Side Low Pressure Switch (HSLP)
On later vehicles the thermal fuse and superheat switch has been replaced by a high side low pressure switch....etc, etc.â € �

I hope this information is useful.

Regards
George

Sure. Any switch can fail


I'm not aware of any different ratings/values for these thermal limiter fuses. But, who knows, maybe the manufacturing is sloppy or they're currently be made to a different spec. AFAIK, the original GM part (6551258) was discontinued ages ago.

Cheers
DD

They're still making them for John Deere Combines. I found some on the interwebs for $10.00.

Oh, they're still available from various sources. NAPA, Advance Auto, etc. Google "35759 Fuse"

Whether or not they're being made to the same spec as the GM originals, I dunno

Cheers
DD