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Old 07-18-2009, 05:26 AM   #1 (permalink)
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Default Intermittent A/C

This may have started longer ago than this, but I first noticed it 2 weeks ago. When traveling with the A/C on, all is working fine. Then all of a sudden, the air from the vents is no longer cool, but getting warmer. A few minutes later, All is fine. I check the connections under the hood, especially the small clutch power connector in the compressor. All tight and look good. Since it is intermittent and cooling comes back, I don't suspect a freon problem.

Fast forward to yesterday, driving on the interstate, once again A/C on and all seems proper, then no longer cool air from vents. Now it lasted over 30 minutes. Then it comes back. I stop for parts for my job, after I restart, all is working again. Drive away and in 5 minutes, I lose cooling again.

Open up my laptop on the seat next to me since I have the FSM loaded on it and a multimeter ( which I keep in the spare tire well ), and start probing. The radiator fans are running. When I shut off the A/C, they stop. So the A/C is triggering them. And I notice also the Idle slows when I shut off A/C, so the IAC is also set to A/C engaged.

No voltage at A/C clutch, go back and probe at relay in under hood power box. As soon as I touch the relay ...... Clutch engages. ??? Bad Connection ???, I shut off car, and pull relay. Look at connections on the box, all look good. With a small screwdriver, open cover of the relay. The attached pictures, I took this morning reveal what I found.

Note, these relays DO go bad. They are NOT water tight. They are used all over inside and outside. Keep this in mind when troubleshooting and intermittent problem in any area that has one of these smaller relays.
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Intermittent A/C-dsc05870.jpg   Intermittent A/C-dsc05871.jpg  
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Old 07-18-2009, 08:22 AM   #2 (permalink)
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Took me three tries to identify that problem in my ex's Tracer when she had it. She took it to the dealer's a couple of times for exactly Ferret's problem, each time came back with the ever popular "Can't duplicate complaint".

Went around tapping relay cases with the plastic end of a screwdriver when the A/C was turned on but not cooling. Finally found the right one, took it to the dealer, walked the service adviser out to the car, popped the hood, and said "Change that relay."

I can't remember for sure, but I think this can happen to any relay that isn't hermetically sealed. Arcing is a common cause of intermittents.

Good find.
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Old 07-18-2009, 08:57 AM   #3 (permalink)
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This AM I'm toying with the idea of putting a capacitor across the contact points to prevent the arcing when they open. The compressor clutch is really a large coil ( inductor ). And anytime you remove it's feed current, there will be an arc. That's what causes this to happen.

I have come up with a value of 1.1uf at min 36v. But is it really worth removing the Power Dist Box to do this? Or replace the relay. Heck this one lasted 5 years.

Knowing me as I do, I probably will do it. Or maybe mount it to the top outside cover of the new relay and coat it in something waterproof.
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Old 07-18-2009, 11:06 AM   #4 (permalink)
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they make relays that stop flyback voltage aka the arc created when a relay opens............most new ones should have it
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Old 07-18-2009, 11:11 AM   #5 (permalink)
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Originally Posted by FPT_RAIDER View Post
they make relays that stop flyback voltage aka the arc created when a relay opens............most new ones should have it
Not Subaru !!!!

Here is a picture of the NEW relay with a 1.0uf 35v capacitor installed under the cover.

I'll report back in 5 years .............. unless the replacement fails sooner
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Old 07-18-2009, 06:35 PM   #6 (permalink)
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I have the same intermittent problem. Can I replace this relay myself? Is this the main AC relay?
Thanks. This has been a vexing problem.
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Old 07-18-2009, 06:43 PM   #7 (permalink)
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#1 ..... WELCOME !!!!! 1st Post. Sit down, browse and be comfortable in our little corner of the Internet !!!


Yes it is, It's in the main fuse/relay box under the hood by the battery. Remove the lid and look at the inside of the lid for the fuse/relay locations.

To remove the relay, I used a pair of pliers. It's held in place by small tabs on each side.

Subaru p/n 82501FC000 ..... retails for $42 ... wholesales for $33.

If you can, go to a junkyard. Subaru uses this same relay all over the vehicle.
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Old 07-19-2009, 11:34 AM   #8 (permalink)
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Thanks very much. Other than Subaru where can I order/buy the relay?
Cheers.

2004 2.5x
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Old 07-19-2009, 12:03 PM   #9 (permalink)
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Since it is made by Denso, some other Japanese cars may use it also.

But if you can find a wrecked Legacy, Outback, Impreza or Forester, you can find them in those also. That Subaru p/n is for a SPDT relay, but they use it as a SPST for the A/C. So an older black relay will work as well.

You can also contact one of the vendors here. Either Jackie at Annapolis in MD, or Ben at Hodges. Shoot them a PM.
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Old 07-19-2009, 04:44 PM   #10 (permalink)
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Update on P/N ... Since this does NOT require the more expensine SPDT relay p/n above, you can use the SPST Denso relay the retails for $11 and discounts to $9.

82501FC100


Let me also NOTE .... On my trip today from NJ to Buffalo, the A/C temp was right on the entire trip !!!!! no warm or uneven cooling. So for me, this HAS been bad for quite a while.

My A/C hasn't worked this well in a few years !!!!!
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Old 07-22-2009, 02:26 AM   #11 (permalink)
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Well, I replaced the relay with one pulled from a wrecked 02 Forester. Problem remains. Should I try another relay? I just hate the thought of the $$ going to the dealer for the repair, esapecially since they cannot replicate the problem.
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Old 07-22-2009, 02:57 AM   #12 (permalink)
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You MAY have a bad relay since it was used, or your problem may be different in which case it has to be diagnosed by someone who can probe and understand the circuit.
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Old 07-22-2009, 06:24 AM   #13 (permalink)
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Quote:
Originally Posted by ferret View Post

The radiator fans are running. When I shut off the A/C, they stop. So the A/C is triggering them.
That is normal since you need proper airflow over the condenser to condense the refrigerant into a liquid.

Have you check you charge? Are you sure its not cycling off on low or high pressure? Whats your fan speed when using the A/C? If your are using low fan speed then the pressure in the evaportator can significantly drop due to lack of heat to boil the refrigerant into a gas. This can happen more when the system is undercharged. This can open up a low pressure switch and shut the compressor down. On the other hand on a very hot day the pressure in the condenser can climb due to lack of cooling for one reason or another and shut down the compresser. High pressure will build because the refigerant is not giving up enough heat to condense into a liquid. This is more frequent with an overcharged system.
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Old 07-22-2009, 12:33 PM   #14 (permalink)
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I'm experiencing a similar problem with my 97 Legacy L. Since I had the car (5 months) I've noticed that the AC compressor kicks on and kicks off quite requently but I assumed it was designed to do this to save the clutch from freezing up or something. Nontheless, it worked so I disregarded the on/off thing. Well, 3 days ago I happended to be charging my sister's AC system and had a half a can leftover so I went ahead and pumped it into my Legacy. A day or two later I noticed that the compressor was trying to kick on and immediately clicked off over and over never staying on more than a second or so each time. Could it be that I've over-charged the system and it is shutting itself down everytime the compressor wants to kick on? I didn't pay much attention to the pressure as I was charging it. What's the proper pressure for this vehicle and can I just let some of the pressure out of it like you'd let air out of a tire? I've read the first part of this thread about the relays but it seems too coincidental to be a relay with the relation to me having just charged the system. Any advice would be appreciated. Thanks
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Old 07-22-2009, 03:00 PM   #15 (permalink)
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Quote:
Originally Posted by Nick D View Post
That is normal since you need proper airflow over the condenser to condense the refrigerant into a liquid.

Have you check you charge? Are you sure its not cycling off on low or high pressure? Whats your fan speed when using the A/C? If your are using low fan speed then the pressure in the evaportator can significantly drop due to lack of heat to boil the refrigerant into a gas. This can happen more when the system is undercharged. This can open up a low pressure switch and shut the compressor down. On the other hand on a very hot day the pressure in the condenser can climb due to lack of cooling for one reason or another and shut down the compresser. High pressure will build because the refigerant is not giving up enough heat to condense into a liquid. This is more frequent with an overcharged system.
My charge was fine, as you also read, the clutch was failing to engage. And was NEVER getting it's +12v. However the relay was. With my meter and later removing the relay cover I proved my gremlin.

Quote:
Originally Posted by dhammond5115 View Post
I'm experiencing a similar problem with my 97 Legacy L. Since I had the car (5 months) I've noticed that the AC compressor kicks on and kicks off quite requently but I assumed it was designed to do this to save the clutch from freezing up or something. Nontheless, it worked so I disregarded the on/off thing. Well, 3 days ago I happended to be charging my sister's AC system and had a half a can leftover so I went ahead and pumped it into my Legacy. A day or two later I noticed that the compressor was trying to kick on and immediately clicked off over and over never staying on more than a second or so each time. Could it be that I've over-charged the system and it is shutting itself down everytime the compressor wants to kick on? I didn't pay much attention to the pressure as I was charging it. What's the proper pressure for this vehicle and can I just let some of the pressure out of it like you'd let air out of a tire? I've read the first part of this thread about the relays but it seems too coincidental to be a relay with the relation to me having just charged the system. Any advice would be appreciated. Thanks
Being a Certified HVAC person also, I would say this is a NO NO. I would never add refrigerant to a system without knowing it's charge level/ super coolant temp or at the least it's High and Low pressure.

My guess, now I can't see, touch, hear or feel it, just from your description is it is overcharged. As soon as the compressor trips on, it reaches over pressure quickly.

These small R134a units were meant to cycle slowly, maybe every few minutes or so. It keeps them efficient. Unlike the R12 units in cars prior to 1994 or commercial R20 units.

Your readings should be:
Ambient Temp 86-95 f
Low side 18-28 psi
High Side 213-242
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