A/C Help!

[smallwwb]

So I now live here in Sunny Hot Southern Arizona and would like to have working A/C. I have done some a/c work before, and am familiar with the process to clean out an old r12 system, flush it, dry it out, and evacuate the system before putting in the new 134a.

So I did all that on my 88dl, new 134a valves, vacuumed and checked for leaks. Everything good.

Then I began to add the 134a into the system, and the compressor will not turn on. It will turn on if I run power directly from the battery. I did that for awhile and it pulled a little more refrigerant in, and now both high and low sides read about 100 PSI, but then it seemed like the compressor was having trouble turning.

I checked each component individually for blockages before I put the system back together, and everything blew air through fine.

My best guesses as to the problem are: bad low pressure switch, or expansion valve not working.

Well, I can't FIND a low pressure switch! There is a switch on the high pressure side between the condenser and the drier, but nothing on the low pressure side.

I do not know how to check the voltage for that high side switch. The expansion valve is up in the dash along with the Evaporator, and I'd rather not have to get at that if I don't have to.

 

This would probably be better off posted on an A/C site, but no one seems to know much about the old subarus.

Anyone have any ideas?

[nipper]

If i remeber correctly these have a rotation sensor on the front of the compressor/clutch. If this sesnor fails the AC will not turn on.

 

You can look there as it is generally a simple system.

 

Have you jumped the pressure switches to confirm they are not the problem?

[Dogbone]

I got my Loyale's formerly non-functional A/C working great recently, so maybe I can help.

 

The "low pressure switch" is technically called the Trinary Switch. It is located on the passenger side of the engine bay, plugged in near the condensor. It is the round plug with four wires.

 

How it works is somewhat complex. It has two sets of contacts.

 

One set of contacts, the set that controls the A/C relay (and ultimately controls the compressor), will open when EITHER the refrigerant pressure is too low OR too high. When the refrigerant is at proper pressure these contacts are closed. [Edit: The wires going to this set of contacts are the Black/White and Red/White ones]

 

The other pair of contacts simply control the condensor fan, and will close when it detects a certain amount of pressure (cooling load) in the condensor, and open when there is not much pressure (cooling load). This simply prevents unneccessary operation of the condensor fan, such as when the car is moving at 55 mph on a mild day and there is already plenty of airflow through the condensor. This pair of contacts does not electrically affect compressor operation.

 

It's dark outside now, and I can't remember the colors offhand, but with the ignition switch on you can unplug this plug, and use a piece of wire to jump between the pairs. One pair will cause your condensor fan to run when jumpered, the other pair you will then know is for activating the A/C compressor relay. Knowing this you can then use this to rule out a switch issue, a pressure issue, or a compressor issue. [Edit: I checked this morning, the Black/White and Red/White wires go to the A/C relay, jumper these out to bypass the pressure switch to check/troubleshoot compressor operation. The other two wires ( Green and Blue?) go to the Condensor Fan.]

 

The infamous "Belt Protection System" is the rotation sensor you see mounted on top of your A/C compressor. This shuts down the A/C compressor if it detects a difference between engine RPM and compressor RPM. Assuming the sensor is still working, you can maintain very tight accessory belt tension, perform frequent accessory belt changes, keep the sensor 3mm from the compressor, keep your fingers crossed, and MAYBE this finiky system will work. Otherwise, you can do what I did, and bypass it.

 

To bypass the "Belt Protection System", first look at this link:

 

http://www.northursalia.com/techdocs/pdf/engine/ljac.pdf

 

And pay attention to the SECOND page, the one with the six pin plug.

 

This plug is located inside your car, right behind the glove compartment. Open your glove compartment door, pinch the tabs so it literally opens all the way to the floor, and you will see this plug.

 

Pins 5 an 6, colored Red/Green and Red/Black, these are the A/C relay ground, and are the circuit that the computer opens if it detects mismatched RPM.

 

To bypass this, simply cut these two wires and splice them together (for mere testing of course, simply use a wire jumper between pins 5 and 6). And note, the operation of the thermal switch for the evaporator is not affected by doing this modification, it will still open and close to allow your A/C compressor to cycle properly, to prevent the evaporator from freezing. This modification merely bypasses the "Belt Protection System".

 

Edit: Here is a snapshot of my modification. This shot is looking right behind the glove box. Notice how I cut the two wires and put male/female plugs on them and just plugged them together (the blue plug on the right). Also for grins I put female/male plugs back on the old wires (blue plugs dangling on the left), so in the unlikely even I want to restore the original circuit I can simply plug everything back together.

 

 

 

 

 

So a few questions, when you hotwire your compressor, does the clutch engage allowing the compressor to turn?

 

And if so, do you have cold air blowing out of the vents? If not, this is where to start. When the compressor is turning and blower fan on, you should have cold air blowing from the vents.

 

From what you are describing, 100 psi on both high and low sides (I assume this is while the compressor is turning) it is either a blockage or a mechanical failure of the compressor.

 

Hope some of this is helpful.

Edited June 18, 2011 by Dogbone
Update wire info and include picture.

[soobie_newbie67]

please dont tell me you forgot to put oil in the A/C system.

 

also, where did you go to have the A/C system vacuumed before you charged the system?

Edited June 22, 2011 by soobie_newbie67

[idosubaru]

when you jumper the compressor on - did it blow cold air?

 

check the sensor nipper mentioned and the pressure sensors, should be simple to test those or jumper them to see if it then turns on.

 

the a/c button in the dash is good?

 

make sure the system isn't overcharged now that you've been having issues.

[skishop69]

Ummmm... 100psi static on both sides. You've over charged the system which accounts for your compressor having problems turning when you hot wire it. Static pressure should be no more that 80psi at around 100 degrees ambient temp. If both sides read 100psi with the compressor running, you have a low side blockage which again will cause a compressor issue. Spec calls for 1.8lbs of R12. If recharging with R134, you can push it to 2.0lbs but no more.

[smallwwb]

Ok thanks for the detailed help guys.

I have some more things to check as far as wiring goes, but here are some things to rule out.

 

Yes I put the proper amount of Ester oil in the compressor and lines after draining all the mineral oil out.

I rented a vacuum pump and did it myself- have done so before. Vacuumed down to 20+ hg for several hours.

I haven't overcharged the system as it only has about 16oz of 134a in it.

When the system was apart, there were no blockages that I could detect- everything blew through good with compressed air.

I jumped the pressure switch by the condenser with no effect. It does make an electrical sound somewhere when the A/C is turned on, and that same sound when the pressure switch is jumped, so I think those are both working.

I thought it might be the expansion valve in the evaporator in the dash, but there is equal pressure on both high and low sides so that rules that out.

100 psi was while the compressor was NOT running- I didn't check when I jumped it- will have to do that.

I was told by an A/C shop that a high pressure side reading of 2.5 times the ambient air temperature was appropriate- they didn't mention low pressure side max.

The clutch on the compressor is working fine.

I believe the compressor didn't blow cold air because there is not enough refrigerant in the system- about 16oz.

 

So...next to check is the "belt protection system." Dogbone, can you just jump the wires from the relay where they plug in to the connector just behind the compressor?

 

One more thing to throw in there: This system is from a carbed ea82, and mine is spfi- does this make a difference? All the connections were the same.

 

Thanks!

Edited June 24, 2011 by smallwwb

[Dogbone]

Ok thanks for the detailed help guys.

I have some more things to check as far as wiring goes, but here are some things to rule out.

 

Yes I put the proper amount of Ester oil in the compressor and lines after draining all the mineral oil out.

I rented a vacuum pump and did it myself- have done so before. Vacuumed down to 20+ hg for several hours.

I haven't overcharged the system as it only has about 16oz of 134a in it.

When the system was apart, there were no blockages that I could detect- everything blew through good with compressed air.

I jumped the pressure switch by the condenser with no effect. It does make an electrical sound somewhere when the A/C is turned on, and that same sound when the pressure switch is jumped, so I think those are both working.

 

The sound you hear is probably the AC relay engaging, on passenger side by firewall.

 

I thought it might be the expansion valve in the evaporator in the dash, but there is equal pressure on both high and low sides so that rules that out.

100 psi was while the compressor was NOT running- I didn't check when I jumped it- will have to do that.

 

100 psi is rather high for static pressure, but system should still be cooling if/when the compressor is running.

 

I like to see at least 40 psi on low side while compressor is running. Regardless, to know if the compressor is actually moving refrigerant, you definitely need to see the pressure drop from 100 psi to something closer to 40 psi on the "low side" when the compressor is running.

 

 

I was told by an A/C shop that a high pressure side reading of 2.5 times the ambient air temperature was appropriate- they didn't mention low pressure side max.

 

The clutch on the compressor is working fine.

I believe the compressor didn't blow cold air because there is not enough refrigerant in the system- about 16oz.

 

It has already been mentioned, 100 psi "static" is higher than would be expected, so it sounds like you have plenty of refrigerant.

 

I'm confused on what is really happening with the refrigerant when your compressor is running.

 

So...next to check is the "belt protection system." Dogbone, can you just jump the wires from the relay where they plug in to the connector just behind the compressor?

 

Not the same.

 

The belt protection system at that plug is looking for a "pulse" from the compressor sensor, and this pulse is sent to the computer located behind the glove box. So jumpering it out the compressor plug you mentioned will only give a solid 12 volts to the computer, which I assume the computer will interpret as a locked compressor. No good.

 

The simplest point that I came up with, and the one I recommend, is the one I originally mentioned above.

 

Again, if you unplug the computer plug at that point, before you commit to spicing anything, turn the AC on and simply take a jumper between the Red/Green and Red/Black wires and see if then the compressor engages.

 

If it compressor engages, you know the Belt Protection is the problem. If the compressor doesn't engage, you have another issue.

 

But the bottom line, if you hotwire the compressor, and the clutch engages and the compressor is pumping refrigerant, you should be blowing cold air. Start with this before you worry about any other electrical gremlins.

Edited June 24, 2011 by Dogbone

[l75eya]

Okay, apologies for bringing back a dead thread, but I've got an A/C pickle on my hands.

I've followed all the advice in this thread for my 87 GL.

I jumped each and every one of those sensors and my compressor still won't engage.

With stock wiring when I attempt to use my A/C the engine revs up the instant I hit the A/C button. It runs at this elevated RPM for about five seconds before (I'm assuming) the sensor attached to the compressor (that reads those little clips that spin past it) tells the car the RPMS aren't matching (because the compressor clutch isn't engaging) and returns the car to it's normal idle.

with all the sensors jumped the car maintains the high RPMs but the compressor still wasn't engaging. Even if I applied power directly to it from the battery. (+12v to the blue wired connector near the compressor)

I assumed it was the compressor itself, so I took the time to swap in the known good working compressor sitting useless in the 93 Loyale with chopped up A/C lines.

After the swap I repeated the process and the compressor STILL won't engage. I don't get it.

It can't be because of a low or high pressure in the system because jumping those respective sensors should bypass those issues were they to exist and run the compressor regardless correct?

I'm at a loss.

[presslab]

You applied 12v directly to the clutch and it didn't engage? Did you measure the resistance? Are you sure it's the right wire?

 

Even with the engine off the clutch will engage if you power it from the battery.

[l75eya]

I will post a picture of the wire I applied 12v to. You mention it will engage with the engine off, how would I notice that? A noise to look for or anything?

[l75eya]

This is the wire I was hot-wiring:

Blue wire connected via round white connecter. You can see the cut and stripped end leading to the compressor. Is this the correct wire?

[presslab]

Yes, the single blue wire is the compressor clutch.  The ground is through the engine block.

 

You should hear a loud click when the clutch engages, and you will feel the pumping when turning the pulley (without belt) by hand.  You can see it too, but it only moves very slightly.

[CarpeNoctem]

Yep if you run a wire from the positive battery terminal to that wire (engine off or on it doesnt matter) you should hear a click as it engages) if not, the clutch is bad.