2G 2gb A/C electrical circuit?

[pauleyman]

I have a non working AC system and I'm trying to diagnose. System worked intermittently last year. Here is what I know so far.
AC switch lights up
AC fan comes on. (suggests ac ecu is good?)
Clutch never engages
System is not low on freon, dual pressure switch shows continuity

I have the factory manual (97 talon Tsi)
but I may as well be reading greek when I look at a circuit diagram.

I've tried to check for power at the AC relay but I get none but I only tested with the engine off/ignition on. Not sure if engine ECU plays a role with AC ECU.
Given the intermittent nature of the AC I'm inclined to think it isn't something mechanical. When it worked it worked well.

I don't have a problem applying a jumper etc but I'm a little out of my element here. Some other posts suggest AC control ECU but I don't know where to start diagnosis.

Anybody got any pointers?

 

[wrencher]

I'd start at the easiest access point of the system to test.
The A/C compressor clutch relay in the underhood power distribution box.

Pull the A/C relay ( it is a standard micro relay)

You must be logged in to view this image or video.

Bottom of this picture shows the pinout for the relay.
Part of the diagram depicts a manual test of a removed relay.
Power and ground applied to 1 & 3
should give continuity with an OHM meter attached to 4 & 5

To test vehicle though....
The sockets or those same corresponding pins of the relay in the relay/power distribution box
Test these too with relay removed
Just properly identify the terminals to know what is being tested etc.

3 is power from the A/C controller/dual sw circuit
1 is ground from ECU to turn on relay in effect compressor clutch engage
5 is power supply key on relay applies to clutch once relays is activated
4 is out put to compressor clutch.

Once the relay is out test the clutch coil real quick....
OHM meter should be about 1-5 ohms roughly between terminal 4 of relay socket to battery ground /block ground.
Otherwise wiring issue to compressor or field coil/ A/C clutch has failed.

Terminal 5 relay socket in relay box....
battery power key on. This is switched power via relay for clutch

I use a fused jumper wire (easily made add on fuse holder with spade terminals attached)
jump 5 into 4 with the jumper wire engine off key on simulating relay activation.
A/C clutch should engage.

If it does you have confirmed that part of the circuit.

Now your into relay control.

Terminal 3 check for power key on & running.
That is A/C controller/ dual sw circuit.
If power missing chase back via diagram thru all components to find source of voltage loss.
Terminal 1 is ECU supplied ground to activate coil in relay and close relay contacts.
^it can be a little more elusive to test with relay removed

So to counter that do some testing with relay installed....

I use bread ties burn the ends off with flame to melt the plastic.
That exposes the tiny conductive wire core.
the little tiny wire makes for a good little insulated ( sans the burnt/exposed wire ends) wires to back probe relay circuits with the relay installed ...
Just make a little "u" shape out of the lil wire over your to test relay terminal/socket & pop the relay back in.

You can use those to test the relay circuits with relay installed in car with it running & A/C requested.

If its missing ground to terminal 1 of relay with A/C selected chase back wiring to ECU.
Or into ECU inputs /outputs.

These tests are simple just study the diagram
Know the circuits involved test with volts/ohm meter to confirm what they are
(have had many instances where something is different car versus service info)
Don't jump anything until the circuits are understood & terminals /sockets are properly identified ....

Many edits later......

You must be logged in to view this image or video.

Below attachment depicts turbo relay box A18x is A/C relay receptacle

 

[wrencher]

In case all the OEM A/C diagrams help Ill add them here;

 

[pauleyman]

Well my meter is broken. Key on engine off the condenser fan works. I swapped the two relays to make sure the AC relay is good and it is. It does not activate when in the AC socket so I obviously have no power there with key on engine off.

 

[chrysler kid]

The relay transmits the go signal of 12v from the switched power source, it does not supply power

Once the switched 12v is applied to the relay, the relay engages the constant 12v battery source to the compressor

So you will want to find out why you aren't receiving 12v from the switched power source to the relay.

I assume you have already checked the fuses for the ac

 

[wrencher]

A volt meter would make quick work out of diagnosing this.
Maybe pick up a low cost cheap one @ harbor freight?

IF its charged & the condenser fan comes on with A/C request...
We can surmise ;
The Compressor ECU is requesting A/C
The ECU is receiving A/C request after pressure switches & engaging fans
(by sending grounds to fan relays / also sends ground to A/C clutch relay =all same outputs for A/C operation)
But the compressor clutch is still not engaging.
The A/C clutch circuit is likely at fault.

So need to test it

Another way to test the compressor field coil itself;

You can also disconnect the triangular connector to the A/C clutch & ohm the compressor side out to ground.
Should be 1-5 ohms
Or with it disconnected jump 12 volts right into that black wire with a white tracer (jump power to compressor side of harness-sole wire in 3 wire connector shell)
The clutch should engage.

If it doesn't engage you found your culprit.

 

[pauleyman]

I did test the coil at terminal four at the relay box 19 ohms. I'll get another meter soon. Freakin Klein unit too. Won't read dc. Everything else works.

 

[wrencher]

Eh ya 19 is high...
Jump it out at the compressor or terminal 4.
Betting it wont engage.
So you would be looking at a A/C clutch or complete compressor replacement in that case.

 

[dustyboner]

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

http://www.mediafire.com/file/dyy6un7pyoihfk1/2g_HVAC.pdf

 

[pauleyman]

I finally got a working meter. I jumpered the clutch and I heard a click. That doesn't mean it's engaging but it's at least functioning. I didn't quite follow the above instructions with the bread tie. I'm assuming that you mean to wrap the bread tie around one of the relay plugins and leave the wire exposed so I can probe it. Can I just go ahead and jumper the clutch with the car running and see if I get a c? Given what I see on pressure gauges I believe the system has a full charge. I don't see any signs of a leak. When I test a Schrader valve it definitely has refrigerant in it. Symptoms I was having was AC would randomly drop out. When the AC did cut on it worked well. Without testing a lot of stuff I wouldn't be surprised if I have a bad AC computer

 

[chrysler kid]

I finally got a working meter. I jumpered the clutch and I heard a click. That doesn't mean it's engaging but it's at least functioning. I didn't quite follow the above instructions with the bread tie. I'm assuming that you mean to wrap the bread tie around one of the relay plugins and leave the wire exposed so I can probe it. Can I just go ahead and jumper the clutch with the car running and see if I get a c? Given what I see on pressure gauges I believe the system has a full charge. I don't see any signs of a leak. When I test a Schrader valve it definitely has refrigerant in it. Symptoms I was having was AC would randomly drop out. When the AC did cut on it worked well. Without testing a lot of stuff I wouldn't be surprised if I have a bad AC computer

Yeah you can supply 12volts to the clutch, as mentioned the unit should function as long as the fans are.operating when the switch is pushed

I've been debating bypassing the AC temp sensor in the glove box. I understand it's purpose for cool to mild days as to not freeze over the evaporator coil, but it seems to kick off the compressor at.its.coldest point.

 

[pauleyman]

I finally got some time. Jumpered coil with gauges connected. You can hear the coil/clutch but compressor never engages. Gauges dont move. At a minimum loks like I have a bad clutch. Im guessing this isnt serviceable with the unit on the car?

 

[chrysler kid]

Correct.

I'm not sure how it's described in the service manual, but I'm confident that the easiest way to remove the compressor and re install is to remove the intake manifold