emerald and aircon
Discussion
Big disclaimer - never done this myself, try it at your own risk etc etc
I haven't got an emerald but I did trace all the wiring when I had a suspect wiring problem on the aircon.
The MBE has a req input and ack output - req is pulled to 12v by turning on the aircon and if the ecu says yes it pulls the ack to earth.
So to get the aircon working with the Emerald you need to fit a relay so that when req wire coming from the pressure switch is at 12v it closes the relay and pulls the ack to earth.
Have a look at the wiring diagrams for the relevant pins to use. You can get at them on the nose connector above the passenger knees and the connector on the heater control box in the passenger footwell. I've pasted my aircon diagnosis guide below which describes how the MBE ECU controls the aircon
I believe req from the pressure switch is pin 15 on the nose connector and the ack is pin A6 on the heater control box
Diagnosing Why the Air Conditioning Clutch Doesn’t Engage
WARNING WARNING WARNING
All of the following is from a 98 4.2. TVRs vary so if in any doubt about wires/colours/pins and plugs don't start waving a multimeter around the electrics
Before doing anything pore over the wiring diagrams from the Cerbera CD and make sure you have identified the plugs and control boxes and the connectors.
If you can't match pin numbers and wire clours with the diagrams do not proceed with the testing.
Earth on the heater contol box is a black wire on pin B3 of the connector with fewest wires
12V is pin B1 on the other connector - green wire
When the AC switch is pressed the heater control box puts a request into the ECU for the aircon to be turned on. The request is 12V on a wire via a relay that goes through the thermostat switch and the pressure switch.
If the ECU says yes it pulls another wire to 0V that energises a second relay in the heater control box that puts 12V onto the AC clutch wire out of the control box to the red wire going into the compressor.
Sooo nice and simple and not much to go wrong
Turn it on and test for 12V at the red wire going to the compressor. (I use the oil filler cap as earth) If it’s live there is a problem with the box of tricks on the compressor.
If no 12V at the red wire then here we go.....
When the AC switch is pressed you should hear a click from the first relay in the heater control box.
If the relay has clicked then you should be able to measure 12V on one or both contacts of the thermostat in the driver footwell (need to measure from the contact to a suitable earth). If only one contact has 12V then the thermostat is open and you have found the problem.
if neither are live check there is 12V at pin B2 white/pink wire on the heater control box. If not the box is faulty.
If both contacts are live then the pressure switch is next in the chain.
Check this at the engine harness connector in the passenger footwell. Its probably hidden up above the roll cage next to passengers left knee.
IIRC its pin 19 and a white pink wire. Its right at one end of the plug. Again test to a suitable earth.
If no 12V then the pressure switch is open and its mucky contacts or the pressure is too high or too low.
If there is 12V then it could be an ECU or heater control box fault.
If the ECU is happy then there should be 0V at the heater control box pin A6 which is white/black
and there should be 12V at pin B5 which is white/green. This is the feed to the AC clutch so if this is at 12V and the red wire at the compressor is not there is a break in the wiring somewhere betwixt compressor and control box.
I haven't got an emerald but I did trace all the wiring when I had a suspect wiring problem on the aircon.
The MBE has a req input and ack output - req is pulled to 12v by turning on the aircon and if the ecu says yes it pulls the ack to earth.
So to get the aircon working with the Emerald you need to fit a relay so that when req wire coming from the pressure switch is at 12v it closes the relay and pulls the ack to earth.
Have a look at the wiring diagrams for the relevant pins to use. You can get at them on the nose connector above the passenger knees and the connector on the heater control box in the passenger footwell. I've pasted my aircon diagnosis guide below which describes how the MBE ECU controls the aircon
I believe req from the pressure switch is pin 15 on the nose connector and the ack is pin A6 on the heater control box
Diagnosing Why the Air Conditioning Clutch Doesn’t Engage
WARNING WARNING WARNING
All of the following is from a 98 4.2. TVRs vary so if in any doubt about wires/colours/pins and plugs don't start waving a multimeter around the electrics
Before doing anything pore over the wiring diagrams from the Cerbera CD and make sure you have identified the plugs and control boxes and the connectors.
If you can't match pin numbers and wire clours with the diagrams do not proceed with the testing.
Earth on the heater contol box is a black wire on pin B3 of the connector with fewest wires
12V is pin B1 on the other connector - green wire
When the AC switch is pressed the heater control box puts a request into the ECU for the aircon to be turned on. The request is 12V on a wire via a relay that goes through the thermostat switch and the pressure switch.
If the ECU says yes it pulls another wire to 0V that energises a second relay in the heater control box that puts 12V onto the AC clutch wire out of the control box to the red wire going into the compressor.
Sooo nice and simple and not much to go wrong
Turn it on and test for 12V at the red wire going to the compressor. (I use the oil filler cap as earth) If it’s live there is a problem with the box of tricks on the compressor.
If no 12V at the red wire then here we go.....
When the AC switch is pressed you should hear a click from the first relay in the heater control box.
If the relay has clicked then you should be able to measure 12V on one or both contacts of the thermostat in the driver footwell (need to measure from the contact to a suitable earth). If only one contact has 12V then the thermostat is open and you have found the problem.
if neither are live check there is 12V at pin B2 white/pink wire on the heater control box. If not the box is faulty.
If both contacts are live then the pressure switch is next in the chain.
Check this at the engine harness connector in the passenger footwell. Its probably hidden up above the roll cage next to passengers left knee.
IIRC its pin 19 and a white pink wire. Its right at one end of the plug. Again test to a suitable earth.
If no 12V then the pressure switch is open and its mucky contacts or the pressure is too high or too low.
If there is 12V then it could be an ECU or heater control box fault.
If the ECU is happy then there should be 0V at the heater control box pin A6 which is white/black
and there should be 12V at pin B5 which is white/green. This is the feed to the AC clutch so if this is at 12V and the red wire at the compressor is not there is a break in the wiring somewhere betwixt compressor and control box.
Edited by mikesr on Tuesday 5th May 22:20
as an aside though, when i spoke to karl some time ago he said they had the aircon working with K3 so give emerald a call aswell and their info plus Mike's diagram will surely see you sorted in no time Gassing Station | Cerbera | Top of Page | What's New | My Stuff