Air Con tri switch test?

[wayneg]

Time to get the aircon working. Has been to shop, previous bill for dryer, regas, Hoses, $600 later and compressor still wont work ( all done by previous owner)
Was told the compressor runs and cold air emits if 12vs given direct to compressor.
I want to test the tri switch on the drier. Is there a method. Should I get 12v going in and out. Any help or ideas to test / check the system. This is all new to me.

[CountP]

Have you tried the aircon relay?

[wayneg]

Ist thing I did was put in a known good spare. I then jumped direct across the relay terminals which I thought would make the compressor run regardless. No joy. This is why I want to test the tri switch as my understanding is it makes and breaks the circuit ( I might be wrong)

[Blknight.aus]

the Tri switch controls the relay....

if yiou cant get it to run by jumping the relay then the problem is in the main feed to the relay or the connection from the relay to the compressor.

the simple way of eliminating the tri switch is to test it for continuity. if its open circuit then its either broken or low on gas (or way over pressure) if when you put 12v directly on the compressor with the vent fans on you get cold air out of the vents then its not out of gas.

[benji]

If the tri switch is working and it's way over pressure then your condensor fans will be on high.

[wayneg]

I have started again from scratch. Checked the Relay OK, Checked 12v at fusbox ok. Checked continuity fusebox to compressor OK. Realised i jumped the wrong terminals on the fusebox before, Got it right this time and compressor kicks in and icy cold air floods into the cabin

So Relay good, fused 12v supply good, Comp Good, Gas I presume plenty.
If the pressure switch controls the relay can I jump that safely.
Should I get 12v somewhere at the Pressure switch?
What makes the compressor cut in and out, is it an internal switch. Can I jump the relay safely until I find the problem?
Can I just unscrew the switch. I read you could as there was a valve behind but don`t want to put the switch into orbit.
I want to be prepared as it looks like the bumper has to be removed for good access.

[DoubleChevron]

Do you have some gauges you can throw on it ... I've only worked on a couple of cars, but the ones I have had a shrader valve behind the switch, so in theory you can unscrew them without releasing all the refrigerant............ However I am willing to post the switch back if it lands in Ballarat :)

if it's low on refrigerant it might be dropping the low pressure switch out (I think I have that right). it's hard to tell anything without a manifold/gauge set.

seeya,
Shane L.

[wayneg]

I am presuming that the gas pressure is fine as the Shop that did the work has commented that the system is fine but specialist Land Rover investigation/ diagnostics required.

[Blknight.aus]

I have started again from scratch. Checked the Relay OK, Checked 12v at fusbox ok. Checked continuity fusebox to compressor OK. Realised i jumped the wrong terminals on the fusebox before, Got it right this time and compressor kicks in and icy cold air floods into the cabin

So Relay good, fused 12v supply good, Comp Good, Gas I presume plenty.
If the pressure switch controls the relay can I jump that safely.
Should I get 12v somewhere at the Pressure switch?
What makes the compressor cut in and out, is it an internal switch. Can I jump the relay safely until I find the problem?
Can I just unscrew the switch. I read you could as there was a valve behind but don`t want to put the switch into orbit.
I want to be prepared as it looks like the bumper has to be removed for good access.

no becasue the relay also has inputs and controls from the AC thermister, the ac switching/brains, the over heating engine turn off ac control and the 3 way pressure switch.

if you jump it on permanantly it will ice up the evaporator and then keep on going till you liquid lock the compressor.

[wayneg]

My understanding now is that a Poss+ signal comes from the Hvac/ecu to the relay. The neg- side of the relay goes through the various switches High low pressure to earth. That in my mind says if the neg- relay terminal on the fusebox goes to earth the pressure switches are closed, in a good state.
That is what I am testing so presume they are good.
Where does the Poss+ come from to activate the relay. Is there something that can fail that would stop the feed I can test ie temp sensor.

I have noticed that when the car is running and the aircon switched on randomly I can get momentary power to the relay and the compressor kicks in for a milli second

[Blknight.aus]

that is most likely the aircon switch thats part of the fan speed controller.

(I need to wedge a 5c piece between the facia of the missus disco to keep that working)

very very roughly...

all of the things that you can control to turn on the AC are positive switching,

all of the things that the vehicle has automated control over to protect the AC are negative switching....

IF

1. the fan speed control works correctly for the AC/heate fan
2. you dont mind your AC only having the equivalent of the MAX cooling setting
3. you can get the AC to engage just by putting a +ve feed to the signal side of the compressor control relay

THEN

you can cut the wire away from the +signal side of the relay and patch in a manually controlled one.

HOWEVER....

this is only a temporary fix until you sort out the probelm with the "controller" side of the AC as you will only really be running on the systems that are designed to prevent the AC system from damaging itself.

[wayneg]

Blknight, Thanks for assisting.
Can I ask am I right in my assumption that the pressure switches are good if I am getting a good earth at the relay terminal.
Would the Evap temp sender failing stop the poss+ feed getting to the relay?
Can it be tested?
Trying to understand Rave gives me the impression this sensor causes the compressor to cut in and out under normal working conditions.

[Blknight.aus]

correct, if earth is present at the -ve side of the signal drive on the relay then the triswitch, temp switches are good.

theres 2 temp switches.

one from memory is in the earth side and is there to prevent the evaporator from icing up.

the other is a temp sensor that chats with the temp control side of the hevac and controls the compressor via the +ve side

but its been a while since I was digging around in there.