[Stromaluski]

The A/C in my forester doesn't work and I'm really not sure why. I've owned it about 2 weeks now.

Background... According to the guy I bought it from, the A/C worked just fine until he was driving down the interstate and something went through the grill and killed the condensor and the radiator. He bought a junkyard condensor and put it all back together and charged it up. Worked for a little bit, then the switch on the dash stopped working (light never came on). He bought a new control head, but never put it in.

I changed the control head, and the light on the A/C button now works; but the compressor still won't kick on. Hooked up gauges to it and it was overcharged, so we pulled out some refrigerant until it was on the low side of good (30 psi/100ish psi). (Took out the a/c relay and jumped it to make the compressor come on). Compressor still doesn't come on with the A/C button... It seems to have an ok charge, but compressor does NOTHING unless forced to.

Anybody have any ideas?

 

[FishingFoz]

So if you jump the relay the compressor does come on correct? Does it come on if defrost is selected (if so skip to step 3)?

If so, there's a few things to check:
1) Swap the relay with an identical relay in the box, see if that works.
2) Shoot the high/low pressure switch. You're going to need a FSM for this, as I don't know the wires, however they're typically a ground if the system pressure is correct, and an open if the pressure is too high or too low. Also make sure the switch is connected. :biggrin: You can also try jumping the switch(s) to check their operation.
3) If the switch and relay is good, shoot the wire from the control unit to the ECU (or BCM). And from the ECU to the relay box.

If you or someone else can post the AC control schematic, it would be easier to help troubleshoot over the Internet.

Edit: On my own research, there's only a low pressure switch - mounted to the top of the receiver/dryer. If there is a high pressure shutoff, I cant find it - again I don't have a FSM. =)

 

[Stromaluski]

Tried swapping relays. No difference. Tried jumping the pressure switch on the drier, nothing.

What do you mean by shoot the switch and/or wire?

And I've never heard of an AC control schematic?

 

[FishingFoz]

Shoot: Use a multimeter to check for proper voltage and or ground in specified locations.

AC control schematic, aka the wiring diagram. If jumping the switch and replacing the relay did not fix it, then your problem is in the wiring or a bad ECU or BCM, or possibly another bad control panel (although doubtful). Having the diagram would make troubleshooting a lot easier, as you don't know what particular point to check on each plug and whether you're looking for a ground or 12v.

If at any point any of this gets beyond what you would normally would feel comfortable doing, I'd take it to the dealer - although at this point you're probably looking at an hourly labor charge to do the electrical troubleshooting.

 

[Stromaluski]

Cool. Thanks for the advice. I'll start checking wires and whatnot next chance I get, which may be as late as next weekend... :icon_confused:

 

[jgrote]

Mine is doing exactly the same thing. I like to troubleshoot from one end to the other, instead of starting in the middle. When I knew the compressor should be on, I pulled the wire from the clutch and checked voltage. I had 13.08vdc. Plugged it back in and clutch still did not engage. I then smacked the clutch and it engaged. My clutch is wearing out. There is a shim you can remove to get it to work again. The reason jumping may work is that you'll get a little more voltage jumping than you will through a relay.

As for pressure switches: On my 00 there are 3 wires going into the compressor; a 2 wire plug and a 1 wire plug. The 2 wire plug is going to an internal safety switch in the compressor. My switch was bad. I cut those 2 wires and twisted them together and all worked as normal. Jump the 2 wires in that plug and see if it works. If so, just jump it.

 

[FishingFoz]

@jgrote That must be the missing high pressure switch for the system, fond it strange it only had a low pressure on the receiver! And that definitely could cause the OPs issues (hopefully).

 

[jgrote]

Probably, mine was just bad. The pressures are fine. The newer ones (SG) have a "combination switch", which I hate very badly, but nothing built into the compressor itself.

 

[Stromaluski]

Thanks for the advice, everybody. Hopefully I'll have a few minutes tonight to check voltages at a couple places.

Seems like if jumping the relay does make it come on, then it's something prior to the relay; so either the pressure switch, ECU, control head, or the evaporation thermoswitch (whatever that is?). I'm looking through the wiring diagram in the FSM, and it looks like those are the only things prior to the relay that would make it not work? Somebody correct me if I'm wrong? :shrug:

 

[FishingFoz]

The evap thermoswitch tells the ECU if the evap is close to freezing up, shutting off the compressor.

If you'd like to post your diagram, it would make it a lot easier to help you. As it stands I have no intention on purchasing a 1998 FSM. But if your AC system is like most, the pressure switches, evap switch, control head, and sometimes other sensors give their data to the ECU, which then turns on and off the clutch relay and rad fans based on the inputs it receives...

 

[jgrote]

All of the various switches that can turn the compressor off are on the line going to the relay, including the switch built into the compressor. These are all low current switches. Since they are all just open/closed switches, you can just jump each of them until it turns on. The one in the compressor is the easiest one to start with, and the least important.

 

[Stromaluski]

The evap thermoswitch tells the ECU if the evap is close to freezing up, shutting off the compressor.

If you'd like to post your diagram, it would make it a lot easier to help you. As it stands I have no intention on purchasing a 1998 FSM. But if your AC system is like most, the pressure switches, evap switch, control head, and sometimes other sensors give their data to the ECU, which then turns on and off the clutch relay and rad fans based on the inputs it receives...

I have no idea how to convert a PDF to a JPG, so I uploaded the PDF copies to my Google Drive.

https://drive.google.com/file/d/0B8i0A6fnwykUY3Y3NFN4UEZPeEk/edit?usp=sharing
https://drive.google.com/file/d/0B8i0A6fnwykUanJtTC1nY1VsT2c/edit?usp=sharing

 

[Stromaluski]

All of the various switches that can turn the compressor off are on the line going to the relay, including the switch built into the compressor. These are all low current switches. Since they are all just open/closed switches, you can just jump each of them until it turns on. The one in the compressor is the easiest one to start with, and the least important.

Sounds like a good plan. :icon_biggrin:

 

[FishingFoz]

The troubleshooting steps you posted seem to follow a most likely to least likely item flow, then down the line as @jgrote put. His view seems the most logical to follow, since you have already checked the most common causes. The wiring diagrams vs the troubleshooting steps would be the most helpful @ this point. Also it would appear the 2 wire connector is a thermal shutoff vs a high pressure switch - this would make more sense as to why it's interacted into the compressor. :biggrin:

 

[jgrote]

High pressure, high temp... Call it whatever you want.:biggrin: We all have our own ways to troubleshoot. I don't do it the same way every time. I kinda use my gut to decide where to start. When I was checking my a/c on my 2000, I worked in this order:
1) I stuck my finger in the schrader valve to see if there was any freon in it, and there was.

2) I checked for 12vdc to the clutch. I found none. I hooked 12vdc to that wire (directly from battery) and the a/c started working.

3) Next I just used my meter to follow the wiring back. I found that I had 12vdc going to one of the two wires for the thermal switch, and none from the other. I deduced that these two wires either went to a switch (that was open for some reason), or the other wire was a ground of some kind.

4) I checked continuity of the other wire to ground, and had none. Therefore, I decided that it would be safe to hook 12vdc to that wire. The easiest way, since the other wire in the plug had 12vdc, was to connect the 2 together. I did, and it worked.

5) I cut the plug off, twisted the wires together, and called it a day.

Until today, I never knew exactly what that thing in the compressor did, nor did I care. It was broken and I bypassed it. Replacing it is cost-prohibitive, so I won't, but I did not hide any of my work, That way, anyone coming behind me can easily undo what I did if they choose. The reason I typed all this, and the moral to the story is, when troubleshooting electrical problems in anything old, follow the voltage. It will show you the answer. And if you modify something like I did, don't hide your work. That's an easy way to anger, or hurt, someone else coming behind you. It also pisses off the troubleshooting gods. I don't know why, but it does.

Edit: I must clarify that this is the type of work you have to do to keep an old heap running. This IS NOT the type of work I do professionally. Everything from step1 to step4 stays about the same, but then I replace the offending part, bringing the unit back to healthy factory spec. If my customers want a bodged together product, I tell them to find another tech. The things I work on professionally can hurt people if not working exactly right.

 

[Stromaluski]

As for pressure switches: On my 00 there are 3 wires going into the compressor; a 2 wire plug and a 1 wire plug. The 2 wire plug is going to an internal safety switch in the compressor. My switch was bad. I cut those 2 wires and twisted them together and all worked as normal. Jump the 2 wires in that plug and see if it works. If so, just jump it.

Hit the nail on the head with this one. I jumped the terminals with a paper clip to check (make sure you don't ground out the paper clip, haha) and sure enough, compressor kicked on. Cut the wires and spliced them together and now I have working AC again. Now to put just a bit more refrigerant in the system so it's correctly charged, haha.

Thanks for all the help, everybody! :woohoo: