Range Rovers Forum banner

Airconditioning guts out at high pressure

2K views 8 replies 7 participants last post by  witjes 
#1 ·
The air conditioning on my P38 continually cuts out on high pressure. Is this the problem with the receiving vessel or what?
 
#3 ·
Probably more with either one of the pressure switches, or the fans not working properly

Are the two electric fans running when the A/C is on?
As Sloth mentioned...

You can test them by jumpering the relays in the fuse box. Jumpering one relay will get them coming on in series (slow) and jumpering the other relay will get them to come on in parallel (fast)

If the fans themselves are physically ok and run properly, then this points towards the pressure switch not working properly to turn the fans on, OR the tri-pressure switch being faulty so that it's cutting the compressor out at a lower pressure before the single pressure switch kicks in to turn the fans on.

Or the other thing I just thought of... if you have a GEMS, then apparently they have an over temperature switch in the compressor aswell, which will shut the compressor off if it gets too hot. That could also be faulty (or cutting the system out because the fans aren't coming on)...

If you haven't already, then download RAVE - which is the workshop manual. It has all the electrical diagrams too, which will be helpful in finding the right pins to jumper to test various parts of the system.

The other way of testing the fans in slow speed is to disconnect and jumper the single pressure switch (mounted on the pipe coming out of the drier). If the fans come on, then they are obviously working. In theory, then you could jumper the correct pins on the tri-pressure switch which will click the fans over to high speed.

Also have a bit of a search on here, as there are quite a few threads relating to the AC system and the testing of the pressure switches.

Hope this helps,
Marty
 
#4 ·
Since replacing the compressor hose, the condenser and one of the alloy pipes on mine last year to stop all the refrigerant falling out within a couple of weeks, mine was behaving itself and working perfectly. About 3 weeks ago I had the switch panel out to replace some blown switch illumination bulbs and, rather than clean 16 years worth of accumulated dust out of the interior temperature sensor, I swapped it for a spare I had. A few days later with the outside at about 22 degrees, it was working perfectly. Left the car in the sun for an hour or so, got in an no AC. By then, once on the move, the HEVAC was showing an outside temp of around 24 degrees. After a while I drove through a thunderstorm and the outside temp dropped to around 20 degrees and the AC started to work again.

As this was a couple of days before I was due to drive to the south of France, figured it wasn't a situation conducive to a comfortable journey, so dropped it into a local garage with AC equipment. The only thing they could suggest was to try re-gassing it. When the system had been evacuated, the machine showed that only 600 grammes of refrigerant had been removed, so they filled it with the 1250 grammes that it should have and all seemed OK. Driving through France it was working fine until the outside temp got up to 32 degrees when it decided to stop blowing cold. Had a quick look when stopped for yet another tank of LPG and the compressor clutch wasn't engaging, despite there being 12V at the plug to it. Carried on and after a while it started working again. While in France it worked most of the time but every so often it would stop. By the time I drove home, it was working all the time and has done since (or at least I think it has, I haven't driven it since last Tuesday as I've been working at Silverstone since then!).

My initial thought was that the interior temp sensor I'd fitted was faulty and not giving a correct output when it got hot so I'll be cleaning up the original and refitting that, but the fact that the compressor clutch wasn't engaging even though there was 12V at the plug to it, does suggest the temperature sensor on the compressor on a GEMS. When I first got the car it didn't work which was due to a dirty connection in the plug to one of the pressure sensors and I initially suspected that but the fact that I had power at the compressor clutch would suggest that was OK and it was entirely down to the clutch not engaging when being told to.
 
#5 ·
Hi

High pressure cut out is a sign of not enough cooling in the condensor. You need to get the pressure gauges connected and see if it realy has high pressure or not. Not enough cooling can be caused by faulty fans, blocked air flow because of dirt and what is mostly forgotten too much freon in the system. If you overfill your system, the condensor will be filling up with liquid refridgerant and the part that is flooded does not contribute too heat exchange with the freon gas causing it too condense and become liquid. During This condensing the volume shrinks dramatically and this causes a decrease in the pressure pulling in new gas from the compressor. If the liquid level is too high it results in cut out of the compressor due to overpressure the same way as when the cooling is insufficient due to the earlier mentioned problems with flow of the air or dirt on the condensor.

Best regards

Jos
 
#6 ·
Have tested the fans not running but ok when hot wired fast and slow, tried running the system with fans hot wired still cuts out tested the system pressure starts ok then rises to red zone in about 10 seconds and the clutch cuts out the pressure drops back and the clutch cuts in again I have bypassed the temp switch ono difference what could cause the fans not to switch on and why is the pressure rising thank you for your help Upton i
 
#8 ·
How do you mean it's going into the red zone? Do you have a pressure gauge fitted?

Either the issue is with the valves in the compressor, or there is a problem in the thermostatic expansion valve. Or there could be too much refrigerant in the system.

Have a look in RAVE, under Workshop Manual - Section 82: Air Conditioning - Fault Diagnosis. There are 2 sub sections listed AIR CONDITIONING FAULTS and REFRIGERANT FAULTS - maybe there is something in one of the descriptions/fault charts that will explain what's happening...

Marty
 
#7 ·
condenser fans are activated via ECM by grounding relay 18 in under hood fuse box me also i don't have fans working with ac on, so i substitute the missing ground signal from ecm by modified circuit to kick the fans in series when the ac compressor clutch engaged as a temporary fix until i inspect the ecm for logged DTC ( for some true or false faults the ecm inhibit the fans driving signal to reduce the load on the engine as i had high vibration with gems before that may cause a knock sensor signal to captured by the ecm accordingly the load be reduced) that my guess as i learned from reading through similar topic. but i am sure there are many members here know much better than me can explain why the inhibition of condenser fans drive signal at the ECM gate.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top