Aircon Q!

[Ferret]

Okay,

For the first time in a long time today the weather has warranted the use of some air-con.

Basically what happens is that the clutch engages for ~10seconds, the air in the cabin chills with a hissing noise and then the clutch kicks out.

The air temp comes back quite warm again over the next 10 seconds and then start again.

Is this normal?

I walloped a pressure guage on the low side and was watching the pressure as it's doing this. The pressure guage is a fairly cheapo one that has green/amber/red zones on it and I wasnt paying that much attention to the actual pressures - basically the guage would slowly drop until it hit the interface between 'good' and 'low' - the system would kick out and the pressure would build back into the middle of the 'good' area.

The aircon was kicking in and out at exactly the same pressures every time - is this normal or should the compressor be running permenantly?

Should I be looking at the pressure sensor switch?

[winfred]

sounds like it's low on freon

[Ferret]

sounds like it's low on freon

I was wondering if this were the case, but my little recharge kit cant push the pressure up any higher - may take it into a specialist for the job to be done then...

[Ross]

Yep, low charge. The gauge is reading the suction side of the compressor, when it shuts off due to low pressure the remaining liquid in the system boils raising the pressure enough to restart the compressor.
I'm assuming you are using the small 12oz can. Try a little more gas and see if things improve.

[Tiger]

Was the AC working last year? If yes, you should be able to charge it. You just have to shake the can to raise the pressure in system until compressor stays on all the time.

If no, then it is possible you got air in system... so it needs to be evacuated and redo.

[bmwrp8]

Okay,

For the first time in a long time today the weather has warranted the use of some air-con.

Basically what happens is that the clutch engages for ~10seconds, the air in the cabin chills with a hissing noise and then the clutch kicks out.

The air temp comes back quite warm again over the next 10 seconds and then start again.

Is this normal?

I walloped a pressure guage on the low side and was watching the pressure as it's doing this. The pressure guage is a fairly cheapo one that has green/amber/red zones on it and I wasnt paying that much attention to the actual pressures - basically the guage would slowly drop until it hit the interface between 'good' and 'low' - the system would kick out and the pressure would build back into the middle of the 'good' area.

The aircon was kicking in and out at exactly the same pressures every time - is this normal or should the compressor be running permenantly?

Should I be looking at the pressure sensor switch?

funny, i had a similar problem before as yours except pressure was fine. when the cabin is cool compressor cluth disengage and does not engage again till you turn of the ac for 5mins..never knew what the problem was till i changed my alternator due to bad charging then the problem with the ac went away. WEIRD

[Paul in NZ]

and once you get it fixed run the a/c evry month for 10 minutes or so....it defogs the car in seconds.

[Ferret]

Was the AC working last year? If yes, you should be able to charge it. You just have to shake the can to raise the pressure in system until compressor stays on all the time.

If no, then it is possible you got air in system... so it needs to be evacuated and redo.

Okay I've had the system evacuated and recharged - the system evacuated 998 grammes and put 1550 grammes of coolant in which ~ 55 ounces - does this sound correct?

The compressor is still cutting in and out, but the aircon is now blowing at an average of 6 degrees celcius (42F) which still sounds a bit high to me...

According to this document here: http://www.e38.org/e32/aircon%20conversion.pdf

1550 grammes of coolant is correct - I wonder if my reciever/drier is shot and needs replacing?

[Tiger]

55 ounce is a TON. Are you sure that is what is needed? E32 is a bigger car with different capacity. The pressure on the low side should be around 26 to 33 PSI when compressor is running.

Yes, compressor will kick on for a while and then shut off for a while... this is normal unless your car is super hot, it will stay on until car is cool and then cycle.

Make sure your aux fan is running when AC is on. This will severely affect the refrigerant pressure reading.

[bsell]

Okay I've had the system evacuated and recharged - the system evacuated 998 grammes and put 1550 grammes of coolant in which ~ 55 ounces - does this sound correct?

The compressor is still cutting in and out, but the aircon is now blowing at an average of 6 degrees celcius (42F) which still sounds a bit high to me...

According to this document here: http://www.e38.org/e32/aircon%20conversion.pdf

1550 grammes of coolant is correct - I wonder if my reciever/drier is shot and needs replacing?

Green sticker on my '95 525 reads 1550 +- 25g of R134 so you are on target.

Need to slap on a set of gauges to see what pressures you are shutting off at. It could be either an out of calibration low pressure or high pressure switch. Or the evap temp sensor is saying things are too cold (freezing up the evap) and stopping the freon flow. Which could come from a stuck open expansion valve (flooding the evap with freon=iced up evap and no airflow=hot air out vents).

You didn't say if the aux radiator fans are turning on. If it is really hot out and the viscous rad fan clutch is not doing its thing and your aux fans are not coming on, then your high-side pressures will go out of range causing the high pressure switch to operate and your clutch to stop operating. What a long sentence! ;)

Seriously, the best you can hope for is a 40 or so degree F drop in temp at the outlets. If it's 95F outside, inside won't get below 55F at the vent. This is with the recirc on, fan speed at max and all controls to full cold (inside air only, please!).

So slap on the gauges (low and high side), stick an instant read thermometer in the center dash vent, set the controls as described above and let us know what's happening.

Brian