Air Conditioning - Range Rover
Regarding converting to R134A:
I sent my compressor to a company in Florida that rebuilt it for $175 (AMC, Longwood, FL, 407-831-0448). The dryer and expansion valve were available from a local auto A/C shop for about $20 each. I had some new hoses made (by the same shop) for about $10 each. I also purchased all new o-rings and a retrofit kit (GM kit, $23) from them.
I flushed the other parts using flushing fluid, my air compressor and a cheap sand blast gun (siphon type).
After that I brought it to a shop to have it evacuated and filled.
And boy does time fly, now that I'm looking at the receipt, it's been 3 years since I did all this. Wow, now that I think about it I've had the RR for over 6 years. Where does it go.......
My compressor stayed the same. But they changed the dryer.
You need to change the dryer and get as much oil out of the system as possible. You can remove the compressor, open the oil fill port, drain it out and flush it (then fill with the proper oil). The condensor is easily blown out with compressed air and flushing fluid. The evaporator is not as easy due to the expansion valve. I do not know if you can flush through it. I had to replace mine, so I flushed it out directly at the evaporator inlet port (flush and oil emptied out in the engine compartment). It's not that bad to get at. Takes about an hour to dissasseble that side of the dash.
At least one shop I spoke with said they would simply change out the dryer and "deeply" evacuate the system. They said the oil would be recovered during the evacuation process. I did not due this, so I can not vouch for it's effectiveness.
Let me know if you need any more details.
These are the numbers AMC Manufacturing had on my receipt.
Part Number: 4271-01 Description: Sanden 709 2-GR CL
A dealer tech told me something interesting about converting our A/C system from R12 to R134 refrigerant. He said that we should use a receiver drier that has a higher setpoint for the pressure switches. This is due to the fact that the R134 system runs at a higher pressure than R12. Can anyone confirm this? Those of you who have converted, are you noticing the a/c comp cycle time for frequent than before? Dave Brown has indicated this issue on his conversion.
You can bypass the pressure switch for a short period of time to determine if it is the pressure switch or refrigerant pressure problems. If the clutch remains engaged when you bypass the pressure switch, you will need to check the pressure of the system. If it is OK, then it's the pressure switch.
If not, there is also a thermostat switch. Part of it is attached to the temperature control. The probe from this control unit is stuck in the fins of the evaporator. It attempts to regulate the temperature of the cabin and also protects the evaporator from freezing.
Symptoms I had were the system started to cycle more and more often, until one day the compressor would not engage. It needed a new thermostat. Not an easy job to replace, but easier than the heater matrix.
The ECU does not tell the compressor to engage (at least not on '87-92 NAS models). The lead going to the ECU tells the ECU the clutch is engaged.
It's a little different by years. From memory, the clutch is engaged by a relay (typically found on the bulkhead.) This relay receives its control signal by way of the; 1)AC/Heat control switch, 2) the thermostat switch and 3) the pressure switch.