Thread: Disco Aircon on and off

Originally Posted by vrdw

Thanks for the info: I'll short the switch and see if the compressor kicks in. I will also check the wiring to the comp/clutch see if there's a break. I'll let you know the results. At the moment it's got a mind of it's own. It kicked in today but lost it's coolness after about ten minutes? Viv

If the 'coolness' goes after running for a while - tends to suggest that the evap maybe icing - after you stop and park for a while - is there a lot of condenser water under the vehicle.

The stat on the evap coil is there to stop serious freezing and should switch when the coil is less than 0 Deg C - it may take a while for the 'ice' to reach the sensor.

Icing is caused by three or four things things

Lack of airflow across the coil
Insufficient Refrigerant Gas
Faulty Expansion Valve
Blockage in the system between the condenser and the expansion device

Expansion valves do fail but very rarely

Blockages - reciever driers or TX valves can get bunged up

Airflow, unfortunately this is a self agravating situation - you have low air flow so the coil begins to freeze - and the ice forms it reduces the airflow even more - and thus it goes on

Insufficient refrigerant - this is the 'normal' cause for coil freezing in auto AC

If you could get me the suction and discharge pressures that would help

..... if not - do a feel test - but be careful as some pipes are quite hot.

Pipe from compressor to condenser coil (the one by the radiator) this pipe should be hot - too hat to hang onto for any length of time

Pipe from the condenser to the reciever drier - this should be warm to the touch - if its still hot then the condenser / and or fans are not operating properly due to air blockages / dirt.

The pipe from the reciever drier to the TX valve or firewall - this should be just the same as the pipe prior to the reciever - if there is a vast difference in temp means the reciever drier has a blockage.

The pipe from the firewall to the compressor (larger pipe) should be cold to the touch at the firewall - if its not cold and all the other pipes are ok then it indicates either a faulty tx valve, a refrigerant overcharge - or strangely enough an undercharge

If it is very cold and icing is on the pipe at the firewall then its overcharged.

I'll do a sketch and post it

basic sketch

May I suggest that ladas's excellent troubleshooting post be copied into another appropriate section for posterity?

Tutorials or something?

Originally Posted by ladas

If the 'coolness' goes after running for a while - tends to suggest that the evap maybe icing - after you stop and park for a while - is there a lot of condenser water under the vehicle.

The stat on the evap coil is there to stop serious freezing and should switch when the coil is less than 0 Deg C - it may take a while for the 'ice' to reach the sensor.

Icing is caused by three or four things things

Lack of airflow across the coil
Insufficient Refrigerant Gas
Faulty Expansion Valve
Blockage in the system between the condenser and the expansion device

Expansion valves do fail but very rarely

Blockages - reciever driers or TX valves can get bunged up

Airflow, unfortunately this is a self agravating situation - you have low air flow so the coil begins to freeze - and the ice forms it reduces the airflow even more - and thus it goes on

Insufficient refrigerant - this is the 'normal' cause for coil freezing in auto AC

If you could get me the suction and discharge pressures that would help

..... if not - do a feel test - but be careful as some pipes are quite hot.

Pipe from compressor to condenser coil (the one by the radiator) this pipe should be hot - too hat to hang onto for any length of time

Pipe from the condenser to the reciever drier - this should be warm to the touch - if its still hot then the condenser / and or fans are not operating properly due to air blockages / dirt.

The pipe from the reciever drier to the TX valve or firewall - this should be just the same as the pipe prior to the reciever - if there is a vast difference in temp means the reciever drier has a blockage.

The pipe from the firewall to the compressor (larger pipe) should be cold to the touch at the firewall - if its not cold and all the other pipes are ok then it indicates either a faulty tx valve, a refrigerant overcharge - or strangely enough an undercharge

If it is very cold and icing is on the pipe at the firewall then its overcharged.

I'll do a sketch and post it

Hi: Seems the pressure is the issue: the pipe from the firewall is not that cold? there again the system has been working fine today so I have to wait utill it plays up again. I haven't found a workshop I can trust to diagnose the problem wo taking all the advice that's been given on this site and narrowing down the problem ao I can tell the guys here what to look for and what to test... will post once the system plays up again. Viv

the gas was recharged recently and like I said it works great some days.

So much for that then.

Ok try this, coming from a dry dusty sandy area try cleaning out the actual aircon switch, I have huge problems with the aircon in my Ford cutting out and this was why as we travel dirt roads the switch contacts get full of dirt, a can of contact cleaner or even compressed air might do it, you dont want to much pressure either, worth a try.