voltage at Compressor clutch

[98RRover]

The AC in my 98 RR 4.0 has been off and on working lately, sometimes great, sometimes not at all.
I stuck a pin in the red wire at the compressor clutch while the compressor was running and cooling perfectly and checked it with a volt meter.

9.1 volts

The clutch was running and the ac was ice cold inside.

9.1 volts cannot be normal can it?

When it's not cooling right, the compressor clutch is not running and the voltage is 0.

[ian4002000]

The compressor clutch is controlled by the HEVAC system, as long as it works I wouldn't look a gift horse in the mouth ! Trace the wire and see if it goes directly to a relay if it does the voltage may be a problem

[98RRover]

With 9.2 volt at the compressor clutch I checked the battery 10.98 and I checked the volt at the alternator 11.5.

[TheTree]

With 9.2 volt at the compressor clutch I checked the battery 10.98 and I checked the volt at the alternator 11.5.

Mate

Those voltages seem very low :o

I suggest you compare it with this test procedure

Sticky: Electrical Troubleshooting Updated 2010 (http://www.rangerovers.net/forum/7-range-rover-mark-ii-p38/28663-sticky-electrical-troubleshooting-updated-2010-a.html)

Steve

[bee utey]

You'll get low voltage readings with a flat battery in your multimeter. Compare your readings with another meter as they all look equally too low.

[98RRover]

I almost went out and picked up a new Alternator today because the reading on my new meter said the output was only 11.5 directly from the alternator post.
I called two local parts stores but neither had a new one in stock, tomorrow thay both said, so I decided to test again with my old Fluke meter.

This time I got a 13.3 out put from the alternator post and 12.5 from the battery.

The new meter was way off. I almost spent $250+ because of the new meter readings.

The reading at the compressor clutch was better, 10.5 instead of 9.2. but still not standard 12V. Should I get a new alternator antway?

[wayneg]

If the alternator or battery are not the issue......
On Gems cars the power comes from the hevac unit, on Thor cars the hevac switches a relay to provide power.
On my latest Thor car the aircon did not work when I got it. It came with a hefty recent bill for aircon work, re-gas, hoses, dryer and fault finding, last note on bill was cant get compressor to engage, seek expert model related diagnostics. I spent ages going through everything, only thing I did not have a Spare Thor Hevac unit to swap over. I Could not get the Hevac to send power to switch the compressor relay. After seeking advice from the forum it was concluded all the important switching is done on the earth side of the compressor so running a switched 12v feed direct to the compressor is an OK fix.
I isolated the 12v feed to the compressor under the main fusebox, cut it and rewired a new fused 12v supply through a relay with a small on off switch on the dash. Easy fix and now my aircon is super cold when I want it regardless of the hevac signalling.

[ian4002000]

If the alternator or battery are not the issue......
On Gems cars the power comes from the hevac unit, on Thor cars the hevac switches a relay to provide power.
On my latest Thor car the aircon did not work when I got it. It came with a hefty recent bill for aircon work, re-gas, hoses, dryer and fault finding, last note on bill was cant get compressor to engage, seek expert model related diagnostics. I spent ages going through everything, only thing I did not have a Spare Thor Hevac unit to swap over. I Could not get the Hevac to send power to switch the compressor relay. After seeking advice from the forum it was concluded all the important switching is done on the earth side of the compressor so running a switched 12v feed direct to the compressor is an OK fix.
I isolated the 12v feed to the compressor under the main fusebox, cut it and rewired a new fused 12v supply through a relay with a small on off switch on the dash. Easy fix and now my aircon is super cold when I want it regardless of the hevac signalling.
Wayne , how are you cycling the air conditioning compressor with your switch and relay setup ? if you are leaving the compressor permanently engaged you will damage the air cond system which is why the compressor goes on and off with the controller to stop this occuring.

[wayneg]

Wayne , how are you cycling the air conditioning compressor with your switch and relay setup ? if you are leaving the compressor permanently engaged you will damage the air cond system which is why the compressor goes on and off with the controller to stop this occuring.

Please re-read my post, All the switching the system does is on the earth side, just providing a new positive path does not effect the usual process. It acts like old school air con, on or off

[p38arover]

For early GEMS cars there is TSB on a mod to increase the voltage to the clutch. I fitted the kit some years back. If you see a gold coloured heat sink (which is actually a high power resistor) behind the RH headlight and have a relay in the RL10 position of the engine bay fuse box, your car has the mod fitted.

Another part of the same TSB is to fit a new cable from the alternator to the battery. It's called the alternator link harness mod.

Another mod which I performed before the above was to reduce the air gap on the clutch. Initially I removed the shim and that worked for a few years. Then I machined a little off the boss of the clutch. I wrote about it on RangeRovers.net here: http://www.rangerovers.net/forum/7-range-rover-mark-ii-p38/35758-air-con-compressor-clutch-help.html
And here: http://www.rangerovers.net/forum/7-range-rover-mark-ii-p38/32567-removing-ac-pulley.html

[98RRover]

I understand what your saying, the switching is on the earth side from the comtrol unit, right?

Will the same setup work on a 1998 RR 4.0?

[TheTree]

Hi Ron that YSB106340 cable simply replaces the cable from the Alternator to the battery, is that correct ?

Steve

[98RRover]

I found my problem with low voltage is a low price meter.

I used my Fluke meter and got about 11.6 volts, so the voltage is OK.

I did find the compressor clutch problem was caused by a bad Expansion Valve. I replaced it yesterday and all is well now.

I now have Ice cold A/C blowing just in time for winter to set in.

[p38arover]

If I recall correctly, there was a TSB for the expansion valve.

[TheTree]

My aircon is behaving weirdly, a lot of the time it is not cold but then it will decide to get a bit cold.

Also the fans seem to run a lot harder than my old beast, but that may just be a side effect of it not being cold.

It has had the mod done so I am looking for the cause of this now

Steve

[TheTree]

Rave also only lists three options for the system not getting cold, expansion valve, low coolant or stuffed pump

It seems it may be worth me looking at the expansion valve

Steve

[davidsonsm]

Steve. Have you carried out the temp differential test before and after the drier? Seem to recall RAVE referring to it.

[TheTree]

Steve. Have you carried out the temp differential test before and after the drier? Seem to recall RAVE referring to it.

Thanks mate I will go through those over the next few days

Steve

[blindin]

As Ron b has mentioned, there are a few mods.
I have personally done the air gap by removing the shim, it worked fine after. I have also added a wire between the alternator and battery, I didn't know about the mod, but the power difference was over 1 volt, so I put a heavy cable in, and been working well.
You could fit a direct feed via a relay to the compressor, having the existing power to activate the relay, I think this is fine, but read above about a resistor, so I would check before hand. There is also a pressure valve which may be at fault. Again, I would start with the easy stuff. I found my fault by holding a screw driver to the clutch, it was magnetic, but not engaging.
Good luck with it.

[TheTree]

Everything points to the expansion valve so I am going to get a professional to take a look at it ... once I replace the engine that is !

Steve