Good old aircon - on the hottest day so far....
Discussion
Not quite the usual question.
Ie. I know where it is. I know where the fuse is located. I have even found the temp control rheostat and have left it alone. The blue light comes on and I have the system gassed up and its not leaking. So why the heck is my clutch not engaging on the aircon pump?
I'm guessing at 3 potential reasons:
- No electrical feed - in which case how do I test this as I seem to have a spool of red wire exiting the passenger side of the pump - should I have a live feed when engaged?
- Pressure switch non-operative - in which case, where the heck is it!
- Clutch jammed or failed - however this appears unlikely as it has worked randomly twice in the last 5 days. On one occasion I was standing outside the car with it idling and I heard the clutch engage and lo-behold I had nice cold aircon - stopped the car and restarted and then no clutch engaging. Doh.
It's been pretty tempremental ever since I've owned the car but the last 2 days weather means I need to sort it out properly. All help appreciated.
Cheers
Ie. I know where it is. I know where the fuse is located. I have even found the temp control rheostat and have left it alone. The blue light comes on and I have the system gassed up and its not leaking. So why the heck is my clutch not engaging on the aircon pump?
I'm guessing at 3 potential reasons:
- No electrical feed - in which case how do I test this as I seem to have a spool of red wire exiting the passenger side of the pump - should I have a live feed when engaged?
- Pressure switch non-operative - in which case, where the heck is it!
- Clutch jammed or failed - however this appears unlikely as it has worked randomly twice in the last 5 days. On one occasion I was standing outside the car with it idling and I heard the clutch engage and lo-behold I had nice cold aircon - stopped the car and restarted and then no clutch engaging. Doh.
It's been pretty tempremental ever since I've owned the car but the last 2 days weather means I need to sort it out properly. All help appreciated.
Cheers
My aircon has similiar issues:-
a) When on the revs drop by 100 but dont come back up again (used to be ok so I assume just needs a 'tune up').
b) My aircon engages each time BUT particularly on VERY hot days it cuts out (ie clutch disengages) and has to be turned on again. ie still blows but the air gets warmer. press the button and clutch is reengaged. Cant work out for the life of me how to fix !
a) When on the revs drop by 100 but dont come back up again (used to be ok so I assume just needs a 'tune up').
b) My aircon engages each time BUT particularly on VERY hot days it cuts out (ie clutch disengages) and has to be turned on again. ie still blows but the air gets warmer. press the button and clutch is reengaged. Cant work out for the life of me how to fix !
The pressure switch is on top of the drier receiver bottle.
The drier bottle is in the front of the passenger side wing in front of the wheel.
Accessible by taking the wheel off and removing the rectangular inspection cover (its below the circular cover for access to the headlamp).
The drier is a thermos flask size and shape. Its held in a P clip type fastener thats bolted to the back of the inspection cover.
A pita to get at and it will be very rusty cos of all the water that comes in through the hole under the front indicator
It has two hoses connected to it and an electrical plug attached at the top. Disconnect the plug and give it a good clean with contact cleaner and spray with wobblyD40 or similar.
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 its 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 suitale 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 clucth 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.
Hope this helps but all the usual disclaimers apply. Author will not be held responsible for any consequential loss or damage if you try following this test procedure. Especially the unbelievably painful back from trying to work upside down in both footwells at the same time and the consequential lack of sleep
(Guess what I was pratting about with over the weekend)
The drier bottle is in the front of the passenger side wing in front of the wheel.
Accessible by taking the wheel off and removing the rectangular inspection cover (its below the circular cover for access to the headlamp).
The drier is a thermos flask size and shape. Its held in a P clip type fastener thats bolted to the back of the inspection cover.
A pita to get at and it will be very rusty cos of all the water that comes in through the hole under the front indicator
It has two hoses connected to it and an electrical plug attached at the top. Disconnect the plug and give it a good clean with contact cleaner and spray with wobblyD40 or similar.
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 its 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 suitale 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 clucth 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.
Hope this helps but all the usual disclaimers apply. Author will not be held responsible for any consequential loss or damage if you try following this test procedure. Especially the unbelievably painful back from trying to work upside down in both footwells at the same time and the consequential lack of sleep
(Guess what I was pratting about with over the weekend)
Mikesr,
Thanks for a very comprehensive reply. In fact you may have hit the nail on the head with one of your first suggestions.
<quote> When the AC switch is pressed you should hear a click from the first relay in the heater control box </quote>
Hmmm. I don't hear any relay clicking. Anyone know where to look for the offending relay?
CossieMetro,
My understanding is that clockwise to decrease the temperature in the cabin. But be aware of the infamous frozen pipe syndrome if you choose to fiddle....
Moderators: Any chance of adding Mikesr as a sticky or in the FAQ as aircon questions appear to be extremely common.
Thanks for a very comprehensive reply. In fact you may have hit the nail on the head with one of your first suggestions.
<quote> When the AC switch is pressed you should hear a click from the first relay in the heater control box </quote>
Hmmm. I don't hear any relay clicking. Anyone know where to look for the offending relay?
CossieMetro,
My understanding is that clockwise to decrease the temperature in the cabin. But be aware of the infamous frozen pipe syndrome if you choose to fiddle....
Moderators: Any chance of adding Mikesr as a sticky or in the FAQ as aircon questions appear to be extremely common.
Edited by apguy on Tuesday 4th July 09:30
mikesr said:
Turn it on and test for 12V at the red wire going to the compressor.
No live feed
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.
Yep got a click
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 suitale earth).
Yep got 2 12v feeds from rheostat
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.
Ahh, I appear to have 12V at the white/pink wire. Its switches from 0v-12v when I hit the aircon button on the dash, however my pink and white is not at pin 19, its the one 2nd in from the right in my piccy.
What I can't locate is the the feed that is supposed to go to the pressure switch and ultimately the big red wire on the compressor...
Edited by apguy on Tuesday 4th July 12:17
Thats the whire/pink as it leaves the control box on its way to the thermostat.
You need to check the white/pink at pin19 on the engine connector. Its up under the dash by the rollcage passenger side. Its on its way back from the pressure switch at that point.
It goes to the ECU and a 0V comes back to the control box to energise the second relay that puts the clutch wire to 12v
You need to check the white/pink at pin19 on the engine connector. Its up under the dash by the rollcage passenger side. Its on its way back from the pressure switch at that point.
It goes to the ECU and a 0V comes back to the control box to energise the second relay that puts the clutch wire to 12v
Thanks for all the assistance so far. But I've now cracked it....
Took the plunge and removed the wheel and pulled out the access panel. Boy what a mess of cable behind there. Saw that on top of the receiver dryer is the pressure switch.
The pressure switch has 2 feeds on one side and 2 outputs on the other. Using the trusty test-lamp I find that out of the 2 feeds I have 1 constant with ignition and 1 switched with the dashboard aircon button. So things are looking good. Test the 2 outputs and I have nadda.
So I'm now thinking that the pressure switch has gone south. Give the pressure switch a clout and now I have a live on one of the outputs. Start the car and whooppee I have aircon. So my diagnosis is that I have a sticking pressure switch.
Its a very simple switch that seems to consist of a plunger that sits in the the receiver dryer and when the system pressure is high enough it rises and makes the contact across the switch. The only anomally I can find is that although I have 2 live inputs only one of the outputs goes live when its working. Doesn't seem to affect the compressor though....
Anyone know where I can get a replacement pressure switch from?
Thanks for all the valuable help.
Took the plunge and removed the wheel and pulled out the access panel. Boy what a mess of cable behind there. Saw that on top of the receiver dryer is the pressure switch.
The pressure switch has 2 feeds on one side and 2 outputs on the other. Using the trusty test-lamp I find that out of the 2 feeds I have 1 constant with ignition and 1 switched with the dashboard aircon button. So things are looking good. Test the 2 outputs and I have nadda.
So I'm now thinking that the pressure switch has gone south. Give the pressure switch a clout and now I have a live on one of the outputs. Start the car and whooppee I have aircon. So my diagnosis is that I have a sticking pressure switch.
Its a very simple switch that seems to consist of a plunger that sits in the the receiver dryer and when the system pressure is high enough it rises and makes the contact across the switch. The only anomally I can find is that although I have 2 live inputs only one of the outputs goes live when its working. Doesn't seem to affect the compressor though....
Anyone know where I can get a replacement pressure switch from?
Thanks for all the valuable help.
Edited by apguy on Tuesday 4th July 14:04
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