Thread: Air con wiring advice needed?

Originally Posted by fender22

Is there a permanent positive wire under the bonnet somewhere I can get a feed off?
The relay idea sounds good, save loading up the whole thermostat circuit. I'll switch the relay with the feed wire to the compressor. The guage of the cable to the compressor is quite light actually? Would have thought it would be a considerable load to pull the clutch in

The starter motor will have a permanent positive on one side of the solenoid.

ditto for the alternator.

Is anyone familiar with the characteristics of the temperature probe leading to the thermo amp ? Does it go open circuit when it gets cold or does it conduct more when it get's cold ?

What would happen if i shorted the wires to the probe ? Would the aircon not start or would it not turn off until the pressure switches cut in ?

Could shorting the probe temporarily damage anything ?

*bump*

Originally Posted by isuzu110

Is anyone familiar with the characteristics of the temperature probe leading to the thermo amp ? Does it go open circuit when it gets cold or does it conduct more when it get's cold ?

What would happen if i shorted the wires to the probe ? Would the aircon not start or would it not turn off until the pressure switches cut in ?

Could shorting the probe temporarily damage anything ?

nornally if you short the two wires on the thermister the op amp turns on.
its a balanced setup comparing the resistance greated voltage in the temp pot and normally wont damage anything.
its ony a small voltage.to test.less than 5V.

i cant see the photos so im guessing its a plastic case under dash unit.
with the deisel defender the temp amp is under the seat and has a temp adjust screw and some inline fuses.

i found these on both sides of the car depending on battery or model.
think they a dirty green.

the fan switches are common cheep and melt easy.best to run relay for each speed.

pressure switch normally in series with the clutch.
normally clutches draw very low amps and melt down before blowing a fuse.most genuine land rover systems dont supply enough volts to the clutch when it starts to wear it often wont engage as the under bonnet heat rises and the clutch requires reshim.

once had a problem with a vehicle with 2 batteries.

the power was conected to one and the earth on the other.when the voltage control circuit switched off the a/c cross fed and caught fire.

Thanks for the notes

Here's what I know so far:

Thermo amp under passenger seat is marked Genelco 14-995S 3649 28(5)F

Has a potentiometer undeneath tehrmo amp allowing adjustment of reference temperature. It is marked (C)old on one extreme and (W)arm on the other. Mine was set a 2/3 towards the cold end.

8 way connector to thermo amp under passenger seat had wires:

Green - Earth
Black - Clutch/Pressure Sw
Red = +12V
Blue - Earth
Yellow - Temp setting Potentiometer on dash
Yellow - ditto
Grey - Temp probe on evaporator
Grey - Temp probe on evaporator

Temp probe was giving ~5.6K Ohm across probe when disconnected from thermo amp at room temp. The hotter the ambient temp, the lower the ohms from the probe.

Temp setting pot on dash seems to range from ~10K on warm to 15 ohm when on cold.

My aircon runs for 10min and then clutch on compressor disengages yet there is power coming from thermo amp red wire. There is no power reaching downstream pressure switch. I suspect there is some fault (relay) in between thermo amp and pressure switch.

Still investigating

So if the thermostat is giving you a call for cooling, but the compressor isn't engaging then it's most likely one of the safeties is tripped. I don'tknow my way around vehicle a/c, but the stuff I work on will have a high pressure switch, often a low pressure switch, ditto a motor overheat protection device (commonly referred to as a 'klixon' in my trade), fuse(s) & some other stuff like overloads which won't be on car a/c as it's powered by the engine.
Of course, you could just have a loose connection somewhere.

If you can find a wiring diagram, that'd be a big help to determine the possible fault.