B

Bob Fenton

Member
The factory fitted air con on my 2007 Defender 90 TDCi has not worked since I bought it last year.

I had the system recharged but that didn't fix the problem and I basically forgot about it until I became motivated by the recent warm spell of weather.

I undertook some basic diagnostics at the weekend with the following results:

1. When I switch the A/C on the button lights up and the fan switches on.
2. The fuse under the dashboard is fine.
3. There is no power getting to the compressor.
4. If I apply power directly to the compressor the clutch seems to engage but there is no cold air.

Based on the above, can anyone suggest what I try next? I was wondering about a possible relay failure but I am unable to identify which of the many relays (under dash and under seat) may relate to the A/C.

Any help would be much appreciated.

Thanks.
 
I found this on another forum and found it helpful so I thought I'd re-post here.

I'll further investigate the problem later with the aid of the diagram.

Puma_Underseat_Relays.png
 
Is the system holding gas? When you had it recharged how much gas was left in the system before they started? (the machine starts by recovering any gas remaining in the system before refilling it, so they should have told you)
 
No, the switch lights up and the fan runs but there is no power at the compressor clutch. If i feed in power manually, direct from the battery, the clutch engages but there's no cold air.

I swapped the relays around last night but to no avail, it seems they are all working.
 
If the system has gas, and with the compressor clutch engaged it still doesn’t work, then it’s likely the compressor is faulty.
If l were you l would take it to an aircon specialist they will probably diagnose it in ten minutes.
 
As above....except the system has a pressure switch so the clutch does not engage and the compressor run with no gas or lubricant in the system. It could be as simple as a wire fallen off the pressure switch which is usually on top of the drier.
 
NeilB said:
As above....except the system has a pressure switch so the clutch does not engage and the compressor run with no gas or lubricant in the system. It could be as simple as a wire fallen off the pressure switch which is usually on top of the drier.
Click to expand...

That sounds simple enough to check. Excuse my ignorance but where is this located?
 
It's screwed into the drier top or the pipe just below.....Its the white part fitted to the green pipe.

AWR2674.jpg
 
An AC system is not hard to understand. A few minutes looking on the web should provide how the system works. All you need to do is check you have 12v at the pressure switch with the engine running and AC on. If you do and the clutch is not engaging then you probably have no gas or a faulty pressure switch. You can jumper the pressure switch if you are sure you have gas. Once jumpered the clutch should engage on and off. There should be a hiss sound inside the cab as the system pressurises. If the hiss continues for more than a minute you probably have low gas.....or a leak! If you jumper the pressure switch and the clutch does not engage then you need to look for where the 12v to the compressor goes missing.
I do wonder how the AC shop checked your pressure without the AC running......
 
You make it sound very simple Neil. :)

As I mentioned in my original post, there is no power getting to the clutch. If I feed power to it directly, it sounds like its engaging but there's no cold air.

Out of interest, it it possible to check the refrigerant level visually?
 
There won't be 12v to clutch if the pressure switch is open. In this heat it will take a long time of running before you notice any cool air out of the vents. It will probably need cool air flowing over the heat exchanger. A trick they use in the Middle East (where I had all my AC problems!) is to pour cool water on the heat exchanger to cool it down and simulate cool air flow. In the picture below the switch is number 4. The heat exchanger is in front of number 1 (radiator). You can't check gas level visually although if the drier has a window on the top you may see bubbles pass as the gas is in a liquid state by then.
1_air_conditioning_condenser.png
 
NeilB said:
... In this heat it will take a long time of running before you notice any cool air out of the vents. It will probably need cool air flowing over the heat exchanger....
View attachment 152081
Click to expand...

That's interesting, I just ran the engine with the vehicle stationary and I gave it about 5 minutes before I concluded there was no cold air.

I'm also guessing that if the pressure switch proves to be faulty, the system will have to be depressurised to change it.
 
First things first, if your compressor clutch is not coming in (which you have proved works) you either have a power supply problem (cables fuse etc ). To low or to high pressure in system. Or control fault hi or low pressure switch.
You need to be sure your system is charged to the correct pressure before you start fault finding, or your wasting your time. As suggested link pressure switches as necessary to prove they work. My guess would be faulty hi or low pressure switch. If you find the compressor runs non stop, it means its probably faulty as it should cut out after 10 seconds or so on the high pressure switch. Good luck
 
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