Need help with ac on 2001 Jag stype!!!
I replaced the pressure switch, new compressor, but still will not engage on its own.
I do remember I replaced the heater control valve this past winter. but that should not effect the ac or does it? I checked and cleaned the grounds behind both headlights and now at a dead end.
should the ac relay be giving a ground or does the computer or ac module sends a ground to the relay via pressure valve?
Thanks Leon

 

Dear Leon,

Run a quick check of relay #8 in the front power distribution box. This is under the hood on the right side (when facing forward). Relay #8 controls the compressor clutch. It routes direct battery power to the clutch.

Remove the relay and check the sockets as follows. The terminals are labeled on the bottom of the relay. A schematic of the relay's guts is printed on the side of the relay.

Connect your voltmeter's negative lead to a good ground. Contact #3 should have 12 volts present at all times. If not, suspect a blown fuse upstream. The exact fuse escapes me at the moment, but I can find it tomorrow.

Contact #1 should have 12 volts when the ignition is on. If not, a fuse is the likely fault. I'll have to find the number tomorrow.

Now switch your meter to read resistance. Contact #5 should show about 20 ohms or so to ground. This is a reading through the coils of the compressor clutch. I'm not positive about the 20 ohms value, but think it was somewhere in that neighborhood. Once again, I can confirm this tomorrow if needed.

Contact #2 is a switched ground, controlled by the AC module. This is what actuates the relay. I didn't actually test this contact on my car, as I found the problem elsewhere before getting this far. Your ohmmeter should show a good ground here when the AC is commanded on, but I'm not sure of all the prerequisites needed for the module to provide that ground. Ignore it for now if you don't see a good ground there, as I don't want to steer you wrong.

Contact #4 is not used.

If all these readings are good (with the caveat from above about #2), test the relay itself. On the relay, connect #2 to ground. Then supply 12 volts to #1. You should hear the relay click, telling you the actuation coil inside the relay is good. With the relay still energized, check continuity between #3 and #5. It should be near perfect continuity. This is the path that provides battery power to energize the compressor clutch. I'm willing to bet large sums of your money that you will find high resistance here. This is what I found today on my '02. I removed the cover and found heavy arcing on the contacts.

Since I didn't have a spare relay, I robbed relay #7. This is for the fog lamps, and figured I can do without them while I wait for a new relay to arrive. I plugged the good relay into the #8 position and bingo, my AC was back in working order.

If desired, you could also jumper across contacts #3 and #5 at the socket for relay #8. This will energize the compressor clutch. Do this with the engine OFF. You should hear a loud click as the compressor clutch engages.

Run these quick checks and let us know what you find. There is more you can do, but this will check the most likely culprits and only take a few minutes.

 

Did you replace the dryer when you swapped the compressor?
Wasted effort if you did not. You must always install a new dryer. Very cheap insurance and all compressor warrantee's require it.

Do you have the JTIS? It's the factory shop manual and you are in severe need of one right now!

Good thing is it's free on this site. Just look for JTIS at the top of the threads and follow the instructions. The forum has it set up to be very easy to install.

It's well worth it!
.
.
.

 

Dear Leon,

You had sent me a few PMs, but I have had very limited online access of late to help you unravel the mystery.

Please post here for all to see, so more people can help. You had mentioned wanting to jumper a control wire to run the compressor clutch manually, but you don't want to do that. You need the pressure switch in the circuit to maintain the correct system pressures.

Keep in mind the system had worked properly at some point in the not too distant past. Find and correct the fault(s), and it will once again perform as designed without the need for jury-rigging.

 

Everything is pointing to PCM not sending a ground to Relay..wiring schematic is showing the #2 pin on relay goes straight to Pcm..and this is the pin I'm getting Nothing.....
Please Help ...it about to get Hot....
Leon

 

Suspect everything else, PCM very very last.

 

Ditto. The PCM itself is highly unlikely to be at fault. There are many prerequisites for the PCM to command the AC clutch to engage. The trick is determining which required input (possibly more than one) isn't being met.

You mentioned the pressure switch was already replaced. What was wrong with it, or was this part of troubleshooting?

When was the last time the system had a full evacuation and recharge? If recently done, did the system work at all, even if just for a short time? If you have a leak and pressure has dropped below a certain point, the compressor won't engage.

On the climate control panel, what does your external temperature show? If this sensor has failed and is erroneously indicating a low temperature, once again the compressor won't engage. (Any time I take my car through the car wash, this sensor gets wet and reads low, and the AC won't run until I get up to freeway speeds and the sensor dries out.) If you don't normally use the exterior temp setting, you may not be aware of the problem.

 

no I do not have the manual, can you give me that site

 

I'm only getting 5volts at Pressure switch is this Right?

 

Ok, thanks for the info, I put a new compressor, dryer, and new pressure switch..my Heater control valve burned out on me this pass winter..and I didn't notice the ac was not working until now..I bought a used Ac control module just to be safe with no luck.
it worked perfect last summer with no problem. The system was vacuum down and recharge with no leaks...
How many volts should be at the Pressure switch? I'm only getting 5Volts

 

It's a HiLo pressure switch normally, to cut off the compressor as needed. It should by cycling on & off.

 

Yes. The JTIS is listed on one of the stickies at the top of the forum. Look for something with JTIS in the title.
Here it is for even easier access!

Details on Win7 64 bit new install method & new JTIS21 S-Type archive

A fellow member has placed it in a very easy to install format.
.
.
.

 

Thanks I'll check it out and get back to You all....You all have school me a lot on the
Jaguar!!

 

Dear Leon,

The AC pressure switch is a variable transducer, not an on/off switch. Here is an excerpt from a factory training guide:

"The PCM receives a feedback voltage signal from the sensor that is used to calculate a equivalent refrigerant pressure. The PCM will cycle the compressor clutch ON / OFF as necessary based on the refrigerant pressure calculation.

In addition, the PCM uses the calculation for control of the radiator fan speed and operation. The PCM engages the compressor after determining if there is adequate refrigerant pressure as compared to the calculated
(displayed) ambient temperature (DATC ambient temperature SCP message).

The compressor clutch is disengaged by the PCM if the discharge pressure rises to 29 Bar (420 psi) and above. Once disengaged by high pressure, the PCM re-engages the compressor at 24.1 Bar (350 psi) After normal system disengagement, the compressor clutch is re-engaged by the PCM if the discharge pressure drops to 20.7 Bar (300 psi) and below." (End quote)

What this means in plain English is that it would be tough to test the switch. More on that in a minute.

Here's the wiring diagram for your 2001:

http://www.jagrepair.com/images/Auto...x2022001en.pdf

Scroll down to Fig 3.4 for details. Per the description on the page above the wiring diagram, the three pins at the pressure switch are as follows:

1 = Reference ground (also for other sensors)
2 = 5V nominal supply (also for other sensors)
3 = 0-5V output to the PCM, decreasing with pressure (only for the AC system)

So basically pins 1 and 2 are for a fixed 5V supply across the resistor inside the sensor. Pin 3 is connected to a variable wiper that moves along the resistor, and supplies a variable voltage signal to the PCM that indicates how much pressure is present. There may actually be a strain gauge inside, instead of a resistor and variable wiper, but the general concept is the same and hopefully easier to understand.

As far as testing the switch, I'm not sure how best to proceed. The connector obviously needs to be connected to measure the output at pin 3. Can you backprobe the connector or is it sealed? If you can backprobe it, make sure you've got 5V between 1 and 2. Then see what you have between 1 and 3. If you read 5V there, that would indicate low pressure.

How low is too low? I do not know. I couldn't find the spec for the low limit when the PCM thinks the refrigerant has leaked out and won't engage the compressor clutch. The training manual quoted above merely mentions "adequate pressure" compared to ambient temperature. (That's why I asked earlier about your external temp reading on the climate control panel.) But if you're reading 5V (or anything close) across pins 1 and 3, I'd suspect either the switch is defective or the refrigerant pressure is too low. That's why I asked about recent evac and recharge.

For all you know, the refrigerant may have leaked out overnight after the most recent service. Service ports can be notorious for not always sealing up 100%, and you'd never think the system was empty because you just filled it. I do not care to discuss how I know this...

 

I have win7 32bit..and the 64bit will not run on my computer...do you have a site for the win7 32bit?

 

Thanks Kr....Your info is very helpful...the outside sensor appears to be working with the right temp. I will back track and let you know what I find..
Does the Heater control valve have anything to do with the ac clutch cycling off and on?

 

Well the JTIS is actually 32 bit and on my 64 bit Win7 machine I need to run it in virtual XP mode.

Might try that?
.
.
.