P38 Aircon probs.

Got the aircon regassed today, and I cannot get the condenser fans to work.

The fans themselves are fine, if I operate relay 13, or 14 the each of the fans kicks in on full speed, if I operate relay 18, they both come on at half speed, so the wiring from the relays themselves is all ok and doing what it should, it just seems that the ecm is not asking for the fans to run when the aircon is switched on.

Also, does anyone know exactly how the Dual Pressure switch (trinary switch) works? The explanation in the workshop manual makes no sense whatsoever. It basically seems to say that the switch has 3 modes, open circuit, closed circuit, or 'shorted'. Not sure how the 'shorted' mode differs from closed circuit.

I also had a problem with the compressor clutch not cutting in, but managed to solve that by removing the shim from the spindle, to reduce the clutch plate gap. Any comments whether I can consider that a permanent repair or not?

Reply to
SimonJ
Loading thread data ...

SimonJ nearly made me spill my Shiraz on 06/06/2006 02:46 by writing:

The fans don't run very often; I've seen a report of the car being left stationary in 40 degrees C and still not requesting the fans - it seems the viscous fan moves enough air on its own.

If it's keeping you cool, it's working!

It should be permanent enough (until you run out of shims to remove!) I don't know of anyone having problems having done that.

Andy

Reply to
Andy Cunningham

I have an odd one too. I have it switched off most of the time & when i want it on i press the button & sure enough cold air comes through. But if I'm in standing traffic after a little while it goes back to warm with no cooling effect & once i get going on a motorway or at speed it comes back on full force!! Any ideas, it doesnt bother me too much as i dont really like aircon, but it's getting warmer now!!

Ta

Nige

Reply to
Nige

That sounds like a fan problem as well, it may be overheating with no airflow through the condenser, and switching itself off until you get moving and cool it down again.

Reply to
SimonJ

The aircon guy reckoned that the fans should come on low all the time the aircon was switched on. (and he was a proper aircon specialist, not a garage which happend to have an aircon unit)

It isn't particularly cold, but does reduce the temp to some extent.

Reply to
SimonJ

Nige nearly made me spill my Shiraz on 06/06/2006 09:25 by writing:

I have seen this happen on another car in fairly extreme conditions. It was a Grand Vitara (hey, it was a free upgrade on the hire car) in Death Valley in California. 115 degF in the shade, and with the engine running waiting to get past some roadworks in the sun, the air temperature around the car reached 160 degF according to the temp. display, and it just couldn't cool that down to much more than about 90 degF.

Back to the RR - I don't think this is the case in UK temperatures, even with the nice weather we've having now. It does sound like it's not getting enough airflow to cool properly, though that's when you'd expect the electric fans to kick in.

Ah... A thought. The HeVAC actually requests the engine ECU to switch the fans on. It is possible that at idle, the ECU thinks there's too much load elsewhere and won't switch them on unless the engine is getting too hot.

You'd need to use something like a Rovacom to monitor the fan request/fan active signals from the ECU, or work you way around with a multimeter to get the same effect to prove (or otherwise) the theory.

Sorry, I don't have a better explanation.

Andy

Reply to
Andy Cunningham

SimonJ nearly made me spill my Shiraz on 06/06/2006 09:43 by writing:

I know that's the case on most cars, but AFAIK most cars don't have the viscous coupled fan as well as the electric ones.

I didn't get interested in what's under the bonnet until I got the rangie, so I might be talking b******s here.

Andy

Reply to
Andy Cunningham

I get the symbol up sometimes, i have put that down to a faulty heater temp sensor as it does fit in with it. Is it possible these are connected?

nige

Reply to
Nige

I'm wondering if my fans are working at all!!

Any idea of a way of checking?

Ta

Nige

Reply to
Nige

Nige nearly made me spill my Shiraz on 06/06/2006 10:06 by writing:

It's possible, or it could be the IAT sensor.

If you're around here (Berkshire) I can pop it on the Rovacom for you.

Andy

Reply to
Andy Cunningham

Nige nearly made me spill my Shiraz on 06/06/2006 10:27 by writing:

You can put 12v straight to the fan to see if it works, or jumper the pins at the relay.

Andy

Reply to
Andy Cunningham

If the P38 aircon is like the Disco II it's a proper climate control system and will do it's best to hold the cabin temperature at the set level. Some cars with "air con" have very little automatic control temperature it's on or off.

My Disco II climate control, automagically adjusts the incoming air temp to heat or cool the cabin as required. The only time I really notice a cold draft is on initial "cool down" after starting up after standing in the sun and when there is full sun shining in when driving.

Try winding the set temp right down, below 16C the Disco II system goes into, full, non-stop, freeze yer knackers off mode.

Reply to
Dave Liquorice

Under the bonnet, fuse box on o/s, the relays are in the top right corner, as you look from the front of the car.

Check fuses 30, 36 and 37 first, they should all be getting a feed with ign on.

Remove relay 13, short pin 3 to earth, and the left fan should come on full speed.

Remove relay 14, put 12+ to pin 3, the right hand fan should come on full speed.

Remove relay 18, connect pins 3 & 5, both fans should come on half speed.(with both relays 13 & 14 replaced in the fuse box)

That's as far as I have got checking mine! I suspect something to do with the pressure switches, but it is a pain to have to vacuum and regas just to replace a switch if I am not certain it is faulty, any pointers on how the pressure switches work would be good anyone!!

Reply to
SimonJ

L322 is the same - even has a pretty sun sensor ;-)

Reply to
Neil Brownlee

Cheers, but i'm in Yorkshire!!

Reply to
Nige

I have it set to 'lo' and it still doesn't seem to cool very well

Reply to
SimonJ

The condenser fans only kick in when pressure switch 2 closes if the system pressure exceeds 17 Bar. Then initially the two fans are connected via the relays in series so operate at half speed. If the pressure rises further to 21 Bar (305 psi!!) then the dual pressure switch closes and switches the relays to connect the fans in parallel with the 12v supply so they both operate full pelt. I've never been aware of my fans running in 5 years! I did have an intermittently weak AC system. This was caused by a sticking pressure balancing valve (or named something like that). This is a valve that balances the pressure in the low pressure and high pressure sides of the system. Both HP and LP pipes pass through this valve where they go through the bulkhead, you can see it if you follow the pipes under the bonnet, it's bolted on the bulkhead. This guy (Martin) knows his stuff if your anywhere within reach of London -

formatting link
Gaz

Reply to
Gazza

If you hadn't put in your original post that you've just had the aircon regassed I'd suggest that low gas was a possible cause. LO should make the cabin decidedly chilly... Might be worth taking it back for them to check they did the job properly.

The fans don't do the cooling of the cabin air they cool the output from the heat pump. If the heat pump is working properly the air should be cooled without the fans at all...

The aircon in my Disco II was naff when I got it but being winter didn't notice for several months. When it finally got hot enough for aircon to be nice it wouldn't cool very well (if at all) but occasionally a bump would kick it into action and masses of cold air would appear. Got it regassed and it's been fine since. Very nice today driving up from Leeds in blazing sunshine and an exterior temp of 26C. B-)

Reply to
Dave Liquorice

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.