AC not engaging on 1999 Forester

[phatline]

Hi,

 

First let me say that I'm a proud new owner of a used Subaru (my first). It's a 1999 Forester S with 138k. It's great, but the AC was out when I bought it. There's a sticker indicating the last AC service was 7/05, so this is apparently a recent failure.

 

The green button light comes on when depressed but the clutch does not engage. I checked the fuse (good) and relay (seems good). I also tested the input signal in the relay socket, and it is 0V regardless of the AC button state. So I think there is a disconnection somewhere between the button circuit and the fuse box, but I'm hoping someone here has useful advice to me before I dive in--it doesn't look easy to trace those connections.

 

I know the fuse works because removing it causes the AC button's green light to go out. I suspect the relay is fine because I tried swapping a known good relay (deicer) into the AC socket (no effect) and because the signal to the AC relay is simply dead.

 

Tried to search for threads here, but the search engine turns up nothing on "A/C" or "AC" even though I manually found some posts with those keywords. I hope I'm not asking a common question.

 

Thanks in advance!

[Legacy777]

Does the compressor clutch engage when the ac button is depressed?

 

If not, I think you're on the right track with the issue being electrical.

 

BTW, the search engine requires a minimum of 4 letters to search. You can search for 3 letter things by using an astericks a/c* or 2 letter word by using two astericks *ac* However you're going to get A LOT of other stuff if you just use the search term *ac*. For that search to be effective, you should add another term.

[OB99W]

[...]So I think there is a disconnection somewhere between the button circuit and the fuse box, but I'm hoping someone here has useful advice to me before I dive in--it doesn't look easy to trace those connections.

You could just be low on refrigerant. There's a pressure switch mounted in the receiver/dryer that won't let the A/C engage if the pressure is too low. Of course, there are several other possibilities (open thermal switches, wiring problems, etc.), but low refrigerant is common.

[phatline]

Does the compressor clutch engage when the ac button is depressed?

 

Thanks! I was out doing more testing. The clutch does not engage. The connector to the AC receives no voltage on any pin. The AC relay does not switch. I see no voltage changes at the relay terminals.

 

I opened up the dash and looked at the AC switch itself (not so easy to get out). Somehow I burned out the bulb, which is going to make future test harder. But I verified that the switch is working, and by working I mean it is grounding a wire when activated (the wire is black with white stripe). I presume this wire is supposed to go to the relay, but I tested and there is no connection. So either the wire is open somewhere, or there is more circuitry between the AC switch and the AC relay (does anyone know?).

 

Thanks for the search engine tips!!

[phatline]

You could just be low on refrigerant. There's a pressure switch mounted in the receiver/dryer that won't let the A/C engage if the pressure is too low. Of course, there are several other possibilities (open thermal switches, wiring problems, etc.), but low refrigerant is common.

 

Thanks! This may be my problem. All I have been able to determine is that the AC button works and the AC relay is getting no signal from it. Is this the point that I should take it in to the shop and have them check the refrigerant? I'm not equipped to do that stuff.

[nipper]

#1 reason ac does not work, low or no rerigerant. There is a pressure switch that will not allow the ac to come on unless the proper pressure is there.

 

Welcome to the faimily

 

nipper

[OB99W]

Thanks! This may be my problem. All I have been able to determine is that the AC button works and the AC relay is getting no signal from it. Is this the point that I should take it in to the shop and have them check the refrigerant? I'm not equipped to do that stuff.

You're welcome!

 

There's a quick check you can do with an ohmmeter, assuming you have one and know how to use it. The receiver/dryer is a cylinder about 2" in diameter and 7" long, having 2 refrigerant lines attached and a 2-wire electrical connector (my info shows yellow and brown/yellow wires for the '99 Forester). That electrical connection is to the pressure switch. The test can be done with the engine off; pull the connector (be sure to depress the lock tab), and check continuity across the switch contacts in the dryer (not the harness). The reading should be very near zero ohms. If the switch is open, it's likely that the refrigerant level is too low; the pressure switch could be bad, but that's much less likely.

 

Since the last A/C work was apparently done less than a year ago (you said 7/05), there seems to be an unacceptable leak rate, and a shop should check for that before fully charging the system. If there's currently no refrigerant charge at all, the dryer may be moisture-saturated and have to be replaced, and the system should be evacuated; definitely not work for a first-time DIYer .

[phatline]

You're welcome!

 

[...]The receiver/dryer is a cylinder about 2" in diameter and 7" long, having 2 refrigerant lines attached and a 2-wire electrical connector (my info shows yellow and brown/yellow wires for the '99 Forester). [...] The reading should be very near zero ohms. If the switch is open, it's likely that the refrigerant level is too low; the pressure switch could be bad, but that's much less likely.[...]

 

Thanks again. I verified the pressure switch reads open. I guess it's time to take it in to the shop. Much appreciated!

[OB99W]

Thanks again. I verified the pressure switch reads open. I guess it's time to take it in to the shop. Much appreciated!

Glad to help. You've done about as much as you can with a multimeter; at least now you have an idea of what to expect when you take it in for service.

[phatline]

Glad to help. You've done about as much as you can with a multimeter; at least now you have an idea of what to expect when you take it in for service.

 

For the record, I took it in to a mechanic. There was no refrigerant. He filled it up and performed a leak test and found no leaks. So either the leak is very small or he missed it. Cost $143 (for labor and 1.5 units of refrigerant), but if it does leak over the next few weeks he will not charge labor to check the system again. It just seems to me like 100% bleed in 11 months (max) would be a fairly large leak.

 

Thanks again!

[OB99W]

It's interesting that no leakage was found, but that apparently you're only covered for labor "if it does leak over the next few weeks". If there's a leak severe enough to be evident in a few weeks, it should be detectable now without too much difficulty. Seems like either the mechanic didn't do much/proper leak testing, the leak really is small, or the mechanic is hoping you won't notice a drop in A/C performance for at least a few weeks :-\ . If the charge doesn't hold for a reasonable time, and your "mechanic" isn't an A/C specialist, perhaps you could try to find one.

 

Leaks can develop in lots of places (including pinholes in hoses, condenser, evaporator, etc.), but the most common locations are at fittings (o-ring seals) and the compressor shaft seal. Leaking refrigerant doesn't leave a visible clue, but it sometimes carries enough refrigerant oil with it to be noticeable; if you see an oily area around a connection, etc (may be dirty), that could be an indicator of a leak.

 

Here's hoping you can keep your "cool" .