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A/C trouble vacuum or electrical?


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18 replies to this topic

#1 Subaru in the hills

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Posted 27 June 2005 - 03:47 PM

The A/C on our '91 Loyale is acting funky. When I push the button the compressor turns on for about five seconds then switches off. If I push the off button then again with the A/C same thing like clock work every time - five seconds. The system is fully charged, and I am getting power at the compressor at first but lose it after that initial run. I yanked the dash only to discover what I thought was an electrical problem may be vacuum related. The hoses coming off the back of the switch board are vacuum so I pulled the A/C one and I've got good suction. Interestingly when I pull the hose off the heat or the defrost or bi-level, minimal suction, (side note, we've been having problems with the heat but figured it was the core all gummed up and haven't wanted to tackle that) anyhow... When I pull the A/C hose off I pushed the button and the compressor still kicks on for that five seconds. Hopefully someone out there is not as confused as I am and could please help me out!

#2 grossgary

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Posted 27 June 2005 - 04:18 PM

check the clutch/bearings in the a/c pulley. if they aren't good they may load the system and cause the a/c to shut off.

how is your idle? if the car isn't idling well the a/c may shut off to prevent further strain on the idling.

i think there's a sensor that disengages the a/c compressor clutch if the rpm's get too low.

and you're sure it's charged properly?

#3 demsgudeatin

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Posted 27 June 2005 - 04:26 PM

I've got the same problem except my compressor still works fine. When I switch to other modes the air only blows out the main vents. The A/C compressor starts up even when I select heat. Checked vacumn and it seems OK. Maybe when you figure out what's wrong with yours, pass the info along so I can fix my problem.

#4 Subaru in the hills

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Posted 27 June 2005 - 04:53 PM

Hi thanks for the suggestions, my idle is about 900 - 950 and I'm sure it's charged so could you tell me how to check the clutch bearings? I'm guessing wiggle and see if there is play? Thanks and if anything works I'll be sure to post findings.

#5 grossgary

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Posted 27 June 2005 - 05:11 PM

you can remove the a/c belt and spin the a/c pulley by hand. it should spin freely when the car is off. the bearings can seize. it will feel lumpy, sticky or maybe even impossible to turn if bad enough.

you'll have to hear from others about vacuum issues.

#6 Cougar

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Posted 27 June 2005 - 05:13 PM

Check the fuse and relay to the compressor. They may be near the right strut tower if it is like the earlier models. I would guess the relay is the cause of this. The vacuum line is for the vent operation, not for the compressor.

#7 Subaru in the hills

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Posted 28 June 2005 - 09:24 AM

Is there a way to test this relay w/o replacing it? Can I bi-pass it somehow temporarily to check if the compressor still kicks off? I have switched the two relays that are by the strut tower and there was no difference. Thanks for calling me off the vacuum system that saves a lot of hunting around!

#8 KStretch55

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Posted 28 June 2005 - 10:39 AM

There's a pressure switch in the system that tells the compressor there's enough pressure from the refrigerant to run. I'm not sure where it is on these, I'll have to look. At any rate, it sounds like you are getting the same reaction as if the system was low on refrigerant, so if you know for certain that it's properly charged I'd try a new pressure switch.

The compressor should run with the defrost/defog selected and I believe the heat to, maybe. The reason being that, especially in defrost/defog, the a/c is used to remove the humidity from the air by running just enough that moisture in the air condenses on the a/c coil. That way when the warm air hits the cold windshield it's dry and doesn't cause fog or ice.

#9 Cougar

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Posted 28 June 2005 - 11:22 AM

Along with the the pressure switch that KStretch55 mentions, my manual for an '88 model shows a water temp switch, AC switch, thermal protector, AC cut relay (for AT only), the switch in the mode panel, slip amplifier, and connection to the ECU. A fault with any of these inputs to the slip amplifier could cause the problem.

I suspect the wiring for the '88 model will be close to a '91 but I don't know for sure. You may want to get a manual for your model year to look things over as some things may be different. The AC control circuit is a fairly complicated circuit to work on.

There may be fuse near the relay on the strut tower also that you should check the voltage at while the problem is happening. It would be nice and simple if there was a connection problem with it.

#10 thesubeguy

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Posted 28 June 2005 - 08:31 PM

i've got all the ac stuff off my rx if you need anything. i can send it along with your b-day present Posted Image let me know if you need anything off something too since i can run to the pull a part

#11 Roundeye

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Posted 28 June 2005 - 10:02 PM

Sounds like your clutch is slipping. First check the gap on your pulser. Make sure the pickup is not too far away from the 3 targets on the clutch. If the gap is right and it still kicks off, you either have a worn clutch, a compressor that is about to lock up or contaminants in the system that is driving the pressures up high enough to overload the compressor ( the later can be seen on a set of gages ). *Note: This applies to Hitachi systems only.

#12 Subaru in the hills

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Posted 05 July 2005 - 08:32 AM

Hello again on this one, I was hoping I'd be able to post the solution but I'm still dealing with the problem! I've got 14.1v at the fuse when switch is off and 13.8v when compressor is engaged then jumps back to 14.1v when compressor goes off but switch is still on. Also with the relay I can activate compressor by pushing down on top of relay, so now I'm thinking it may be relay after all. I tried to get a new one from big box auto parts store and the one they had for it didn't look like mine or work at all I may have a trip to a dealer or hopefully excuse to go to junk yard! I'd love to have a wiring diagram or manual with more electrical info. - any suggestions. The A/C pulley is real smooth with belts slacked. Thanks again, I know the answer is right around the bend!

#13 azsubaru

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Posted 05 July 2005 - 08:42 AM

I'm having AC problems, too, and recently went through the same troubleshooting that you are going through. On my 91 Loyale, there are two relays side by side back in that right strut area. They are identical, so you can easily switch them to troubleshoot. Very unlikely that both would be bad.

#14 Cougar

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Posted 05 July 2005 - 09:22 AM

If the relay is not working then you try swapping it with the other relay as was mentioned. If the other relay doesn't help then most likely there is no voltage getting to the relay coil to turn it on and you need to trace that wire down to see what the reason is.

#15 Subaru in the hills

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Posted 05 July 2005 - 09:46 AM

Is the relay coil inside the relay? Sorry if stupid question but you've been a great help so far and switching those relays did not change the situation. When I take relay out I've got 14v at relay plug but how do I test what's coming out? Am I in over my head or what.

#16 Cougar

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Posted 05 July 2005 - 10:41 AM

Yes, the coil is in the relay. A relay is just really a switch that is controlled by applying power to a control coil and it magnetically closes the switch. Usually they are used to turn on circuits that require a fairly high amount of current to power the load. Pretty simple stuff when you see how it works.

You stated earlier that when you forced the relay closed that the compressor worked ok and also that it seemed to work with the switch also. This means all is ok with the power supply circuit, but if the compressor is not staying on when it should be then other things could be at fault.

#17 Subaru in the hills

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Posted 06 July 2005 - 11:16 AM

Could someone tell me where that pressure switch is located? I've been tracing one wire that comes from relay and has 14v when comp. is off but has almost none when running. Traced it to this mini board that reads as connected with almost no volts when comp is on and 14v when off and not connected. This goes to the gold box mounted behind glove box, is it a resistor? Does anyone have any numbers on what the resistance should be here at this box, hopefully this isn't the blower resistor and I've just wasted more of our time..... my head hurts.

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#18 Cougar

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Posted 06 July 2005 - 12:59 PM

The component you show in the left side picture looks to be a diode from what I can tell. I'm not sure what the little box is but it may be the slip amplifier for the AC. It is not the blower motor resistors.

The voltages you saw are most likely normal. It sounds like you were measuring the contacts of a switch or relay that closes to a ground connection when the system is on. The voltage will be across the load then when the circuit is functioning. When the control switch is open and the circuit is off, the voltage then appears across the open connection since the resistance is infinite there. Ohm's Law must prevail.

#19 Subaru in the hills

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Posted 07 July 2005 - 09:55 AM

Yee-ha good news to report. After much frustration and threats to take the little red wagon in to a pro. my father-in-law saw how I could make it work by pushing on the top of the relay and said "lets hook them back onto the brackets" so being at the end of my rope I did and there she goes! Not kicking off after 5 sec. cool air blowing inside, ahhhhh. So anyway on the top of the relay there's a bump that fits into the bracket's pocket and if the relay is slid on backwards or if it's just hanging unattached it didn't work, so thank you all so much for your help!




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