2005 Legacy Manual AC troubleshooting

[sub]

EDIT: This is a 2006 Legacy, not 2005. Sorry.

 

Looking for someone to confirm the logic and validity of this diagnosis. My AC will sometimes work, and sometimes not. Sometimes for just a bit, sometimes longer than others. No real rhyme or reason to it that I can tell. Lately it seems to work less and less. For instance, I just went out and started it this morning, and AC worked for about 1 minute blowing cold air, then the air turned warmer, to about ambient outside temp.

 

Had it looked at and they say:

* Found A/C clutch engaged once but now it will not come on unless relay is bypassed.

* Checked charge in system found it was low

* A full charge is 15oz and it only 9oz. Recharged system.

* Suspected high pressure switch but after testing it found ground signal is not getting to the compressor clutch relay even if pressure switch is bypassed

* Appears to have a wiring short or other issue in the harness, need continued diagnostic time.

 

The suggestion at this point is that the wiring needs to be traced, looking for a short or bad connection.

 

Does the testing methodology that was used seem complete and valid to determine a wiring short?

Anything else that should be tested before starting to dig into wiring harnesses?

 

Thanks

Edited August 24, 2020 by sub
Model year was wrong!

[Max Capacity]

http://people.csail.mit.edu/ilh/vacation/

 

The service manual might help.

[Max Capacity]

I think there is a discussion on here or over on the Outback.org forum about this issue.

 

https://www.subaruoutback.org/forums/

[sub]

http://people.csail.mit.edu/ilh/vacation/

 

The service manual might help.

Thanks for that, I'll see if I can gather anything useful from that.

I'm not really convinced it's a wiring issue, just based on behavior, but I don't know the AC systems well enough to say whether things were tested properly by the shop or not. I'll keep poking at it.

[apexi]

So, even with the proper charge at around 15oz it still only works sometimes? Or that was the symptom with 9oz? I wouldn't go too crazy if it was acting abnormal with a low charge

[sub]

So, even with the proper charge at around 15oz it still only works sometimes? Or that was the symptom with 9oz? I wouldn't go too crazy if it was acting abnormal with a low charge

No, it’s still not working properly. No change with the recharge to 15oz, same behavior as with 9oz.

[blue wrench]

I don't know exactly what the deal was with the following, but almost all 05 Legacys I have worked on did not have cabin filters when I came across them during a major service. The compartment is there it was just empty and it did not have the access hole to easily reach the cabin filter, you need to take the entire glovebox panel off. The later years do come with an access hole covered by a bracket and some dash fabric.

 

The reason I mention this is because the lack of cabin filter causes the evaporator to become plugged with dust,dirt, etc. And does not allow to the temp sensor that is installed right on the body of the evaporator to read accurately.

 

The only way to really check though is to completely pull the evaporator from the dash. Yes it is very doable in the car, no dash removal required. It isn't the most complicated job but it's not exactly fun if you're doing it for the first time because of the cramped space you have to work around.

[sub]

I don't know exactly what the deal was with the following, but almost all 05 Legacys I have worked on did not have cabin filters when I came across them during a major service. The compartment is there it was just empty and it did not have the access hole to easily reach the cabin filter, you need to take the entire glovebox panel off. The later years do come with an access hole covered by a bracket and some dash fabric.

 

The reason I mention this is because the lack of cabin filter causes the evaporator to become plugged with dust,dirt, etc. And does not allow to the temp sensor that is installed right on the body of the evaporator to read accurately.

 

The only way to really check though is to completely pull the evaporator from the dash. Yes it is very doable in the car, no dash removal required. It isn't the most complicated job but it's not exactly fun if you're doing it for the first time because of the cramped space you have to work around.

Oh shoot, I just noticed that I fat fingered the title of this - it's actually a 2006! Sorry for that. I wonder if I can edit the title....

[blue wrench]

It may still be worth checking out if the production date of your car was close enough to the 05MY. If you can pull your glovebox you will see if the access hole is there or not.

[r.lee89]

You try to put the horn relay into a/c clutch relay temporary to see if that fixes the problem.

 

It seems from the wiring from relay to the clutch is ok. The problem seems to be from the a/c button to the relay is the issue.

You can also put the a/c relay out and test for power when its not working it should have power at 2 terminals of the relay with the a/c on.

[sub]

Ok, good idea. I've already tried swapping relays, no change.

I've checked voltage at the relay terminals (85 and 86 as labeled on a relay) Here's what I see:

* When tested against a ground screw, I get 14V from one terminal.

* When using the other terminal as ground, I get nothing. This is tested with the AC switch on and car running.

 

With the AC on, shouldn't I get 14V when testing across the relay terminals?

[r.lee89]

Test the other terminal again to B+ and you should read above 13V if the system gets grounded.

If it still reads nothing then there's either a break or the something is telling it to not to turn on.

The next step would be to check the wiring coming out of the ECM

[sub]

I've tested as far as I can, had it looked at again by the same shop and the diagnosis was either a bad connection to ECM, or ECM itself. Connections were reset but problem persists.

I think at this point I might get a second opinion from the dealership before going down the ECM path. If I'm able to resolve this I'll update.

[bluesuby]

Browsing this morning and found some explanations why the a/c isn't performing. I too have a problem which is the a/c is not putting out 100%. The unit is fully charged and the compressor cycles on/off as it should. When the ambient temp reaches high 80s I sometimes get good cooling but if on a trip over an hour it will suddenly fall off. The compressor continues to cycle, and the air coming from the vents is slightly cool, but if the sun is out on a cloudless day things are not good. I removed the dash panel to make sure the drain hose isn't plugged. It's ok. It also looks very clean in there despite Subaru stopped puttting cabin air filters in late 2004-sometime 2005 because (I was told) the replacement of filters involved tearing the dash out. I read up on the system and found there's an expansion valve but it looks like the system must be evacuated to replace this part. I am no expert on a/c and this job is beyond me....if indeed that's the issue. Any ideas on what might be causing the problem? I think someone mentioned a temperature sensor on the evaporator. Is that part easily changed out? I'm probably going to visit a professional shop, but since it's now September and weather relief should be here soon. I hate to spend hundreds on a fix before next June. My car has 183,000 miles and Murphy's Law says as soon as the job is done, someone will t-bone me and total out the car. Edited September 5, 2020 by bluesuby
spelling error (June)