I changed my AC compressor and thought that was the problem with the AC not turning on. I have also change out the relay. Now I am wondering if the car is not sending a switch on signal to the clutch/compressor. I put a voltmeter into the plug that goes from the relay into the clutch.

Should I see a jump in voltage in the wire to the compressor when I switch the AC on in the car. I would think that the wire I underlined in yellow below should go to 12-13 volts when I switch on the AC. Any thoughts?

With the AC off and the car on I read a voltage of .08, with the car on and the AC on it actually drops to .04.

 

I'm sure someone more knowledgeable will reply, but my first though is if there is enough freon charge (pressure) to create continuity across the A/C pressure switch? Also, if the pressure is too low, seems like the clutch relay may require jumping while adding enough freon for the pressure switch to make contact. Fortunately now for me, I have a local A/C guru that I can lean on.

 

after flushing the system, putting in the compresor and dryer I used a vacuum pump and got to a steady -30. To and add 134a I turned on the engine and added through the low side using a manifold setup (followed procedure from EricTheCareGuy on YouTube- he is pretty good). The system only took maybe 5 to 8 ounces of 134a before it stopped accepting it. I assumed this was because the AC system was not kicking in to pull in the refrigerant, but I could be wrong and maybe I have some other issue.

I guess I may have a chicken and egg problem. Is the compressor not turning on because I cannot get enough 134a in or can I not get enough 134a in because the compressor is not turning on???

 

I am having the same problem. Can't figure out the easy way how to jump the ac comp clutch to make it draw in the Freon. After tracing it out, I am thinking it's that 6 way combination AC Freon switch in front near the engine oil coolers. Not jumping that whatsoever,. When I get back on it, I will skip all that and apply 12 volts directly to the AC comp clutch by unplugging the clutch and jump it off that way with a home made 12 volt jumper from under the car. Pretty sure it's just spade terminals in there. A hot and a ground to kick that clutch in until it sees enough 134a to continue on it's own when reconnected properly. Been a few years since I replaced the comp unit & clutch combo. But there must be a different way thru a relay I am sure.

Anybody know of a boot or under bonnet relay that we can jump to accomplish the same thing? Those AC comp connectors are a bitch to get to down there by the engine mounts.

 

When installing the freon, I use a small bucket of very hot water to put the can into ( upright). The hot water increases the pressure in the can and allows more of the R134a to move into the system. Otherwise, your input will stop when the pressure in the system equals the pressure in the can ( hence the partial fill). HTH.

 

Marc, on my 02 XKR, under the brake booster cover, there is a cover over 3 relays inline. The forward most is brown (other 2 are black) and is my clutch relay. I can remove that relay and with a paperclip, jump the socket at pins #3 & #5 (see bottom of relay for numbering) to engage clutch)

 

Thank you very much Dr D. That's the exact medicine I needed. Jaguar Forums is the best. Always a friend around to cover your back.

Sorry but all my relays are black colors for 3 years now. Replaced 40+ of those relays with new ones as a PM. This fixed 2 very serious issues with my 01' XKR.
One was refusing to kick in the starter when warmed up on very rare & random occasion, and the other was sudden engine shutdown upon a hard shift to second gear on less than perfect roads. Found the relays on ebay in bags of 20. They work well.

Opened up all the old relays I replaced. The points looked perfect on every one of them.

Helping out a friend with his 2005 Volvo 60, 5 cylinder. Minor collision ruptured it's condenser but all repaired now, and we tried jumping the compressor the exact same way, paper clip the relay. Starting to think something happened to it, because not getting any reaction with the paper clip. BTW, that car's AC relay is clearly identified in the box's cover.

 

Glad to help.
Since I too had purchased a "black relay" at Advance Auto, allow me to attach a thread with WhiteXKR's and my comments about relay transient voltage protection.
https://www.jaguarforums.com/forum/x...y-fuse-114672/

 

This concerns me. Didn't know there was any differences. Very good info right there. Thanks for the heads up.
I haven't experienced any abnormalities for years already now, so I assume the cheap Chinese relays I used must be protected since everything works as it should.
I see the brown relays only have 4 pin outs. All the ones I switched with are 5 pin outs and work the same.
I had one limp mode, but that was after I washed the engine, and it cleared itself in about an hour or so of drying out. This is one thing about the XKR's, even in limp mode, they can still keep up with the traffic.

 

Marc: The Jaguar relays show a component (resistor) across the coil on the schematic molded on the side of the plastic relay case. My black one has a schematic molded on the side of the plastic relay case but without the resistor. (Sorry, but I do not know the correct resistance value) Maybe your black ones have a schematic molded on the side also.
Sorry for any appearance of highjacking the thread.

 

The component is actually a diode. It's there to prevent voltage feedback from the relay coil when the compressor is turned off. Especially important if the relay is driven via an ECM, because that means that the ECM is using some form of transistor to switch the ground of the relay. This feedback voltage can cause damage to those transistors. The feedback voltage also can cause the points in the relay to stick over time. Used on many relays where a motor is involved ( such as the electric cooling fans, AC clutches, etc).

Here's a short , fun little video that sort of demonstrates this.

 

Hello Darb:
I actually installed a diode across my Advance Auto relay in 2011 which is still intact ILO a bypass resistor. At that time, WhiteXKR was even referring to a diode in the original earlier post as I assume that he had not learned of such a resistor at that time.
Here is that earlier thread starting around #7:
https://www.jaguarforums.com/forum/x...03/#post382711
Although I have some electronics training (1960's), I am more than indebted to WhiteXKR's (Steve's) expertise and for his providing innovative electronic products for Jaguars such as ours.

 

My new relays have schematic printed on them, and doesn't show any diode or resistor. The relay cover appears to be sealed with glue or high frequency welding.


I ohm'd it out and cannot detect either.

 

Appears to be unprotected. Ohming out across such relay coils, protected or not, will virtually display a short circuit. In my case, I removed the cover to know for sure.