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Compressor relay

Tiny
MRLULLABYE
  • MEMBER
  • 2004 TOYOTA MATRIX
  • 4 CYL
  • FWD
  • MANUAL
  • 110,000 MILES
I changed the clutch in my 2004 Toyota Matrix this weekend, and low and behold the AC clutch will not engage now. I am not a complete noob so here is what all I know.

The 10 amp fuse under the dash is not blown. We actually tested all of the fuses under the dash and under the hood.

When you have the AC button pushed with the car running and fan on, the AC light comes on, the engine revs slightly to compensate for the AC clutch engaging, but the AC clutch does not engage.

If you jumper the 4 post relay right under the hood the clutch will engage and build pressure until there is about 40 PSI on the low side. Also if you jumper + and - to opposite sides of the small little connectors on the relay you get continuity across the fat post on the relay and that good old relay functioning snap, so it seems ok.

The fans spin when the engine is running.

If you jumper the thing that is mounted in the high pressure line I can only assume is a pressure switch the cooling fan under the hood will come on, if you jumper it differently it will come on higher speed.

It really looks to me like it ought to work, there seems to be enough coolant in the AC system to trigger the low pressure switch. The clutch is connected otherwise jumpering it at the relay would not fire it. The switch in the cabin works otherwise the engine would not rev slightly when it is engaged and rev lower when it is not engaged.

The fan works. Is there any other sensor I am missing? Maybe it is somehow connected to a sensor to tell it when the engine is running?
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Thursday, April 16th, 2009 AT 9:51 PM

12 Replies

Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
I know there will be more feedback than this , but you say you have 40 pounds of pressure. There is a difference between the pressure and actual freon. the freon level might be low enough to keep it from turning on. you can try to add more freon not the gas. There is instructions on the can telling you which way to have the can when filling. the unit. Go to how does it work section, it will give you more insights on it.

the compressor relay is called a M/G ctrl relay Here is the relay location and how to test it with the air conditioner wiring diagrams so you can see how it works.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.

Cheers
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Friday, April 17th, 2009 AT 8:57 AM
Tiny
MRLULLABYE
  • MEMBER
  • 5 POSTS
I'll look into it. I know there is the oil charge in the system, but I always thought the coolant was completely gaseous in the system, when not running and only temporarily liquid if at all in at certain locations through the whole low side high side cycle.

The AC relay is $72 from toyota, and I am contemplating buying one just to try it, but it seems a little steep just to try.

Would I be well advised to try and jumper the low pressure switch to see if that makes a difference? There are 4 pins on it so I don't know which ones to jumper.
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Friday, April 17th, 2009 AT 9:38 AM
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
The system needs two things lubricant and freon. The freon is in a gas state until it goes to the compressor then changes to liquid. That what cools the car. You can have pressure without much freon. Most places will suck out the system then recharge it. You can try crossing it over on the low end. I am having problem getting into electrical diagrams have you checked out the how it works section on the left. It will explain some more on the system. There is also a section about problems.
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Friday, April 17th, 2009 AT 11:17 AM
Tiny
MRLULLABYE
  • MEMBER
  • 5 POSTS
I did indeed check the how it works section, but I still don't see anything about the amount of freon vs the pressure. I think those two are pretty much conneced like if you don't have enough coolant aka freon you won't have enough pressure.

I could be wrong, but how else would you check it if not by pressure. It isn't exactly like there is a freon dipstick.
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Friday, April 17th, 2009 AT 1:28 PM
Tiny
MRLULLABYE
  • MEMBER
  • 5 POSTS
It lunch I attempted to jumper the pressure switch again. No dice. It is a 4 wire plug and I was only able to jumper 2 at a time so it is possible that there is some combination I was unable to hit, but in my mind that sort of closes the loop on it being a pressure switch or lack of coolant problem.

I also ordered a AC clutch relay and will try that out in about an hour.

It came to my realization that the WOT sensor could be stuck open causing it to shut the AC clutch down, but there is no unusual revving or CEL lights. SO I am not sure how much persuing that is worth.
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Friday, April 17th, 2009 AT 2:10 PM
Tiny
MRLULLABYE
  • MEMBER
  • 5 POSTS
For what it's worth it was the A/C relay. We tested it and the old one seemed to work, but perhaps our voltage was too high or something. I put another relay in it and it works like a champ.

Thanks for the help.
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Friday, April 17th, 2009 AT 7:00 PM
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
I am glad you figured it was the relay and now it works Mike.
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Friday, April 17th, 2009 AT 9:38 PM
Tiny
APURCHASEDRAG
  • MEMBER
  • 1 POST
I have a 04 matrix and this forum was what I needed to read. My matrix had the exact same symptoms so I replaced the relay and my a/c works like a charm. Thanks for the leg work it made my troubleshooting process much easier :)
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Thursday, May 27th, 2010 AT 1:22 AM
Tiny
MPENA1607
  • MEMBER
  • 1 POST
I had the same problem and your suggestions helped me to solve the problem. I replaced the relay ($16 including tax) and now the AC is working
Thanks so much for the help
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Saturday, February 23rd, 2013 AT 7:02 PM
Tiny
WAI
  • MEMBER
  • 1 POST
I had this problem as well I found the fuse was out thanks for the diagrams above really helped me.
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Thursday, June 2nd, 2016 AT 10:47 AM
Tiny
SCRAPDOGGIE
  • MEMBER
  • 1 POST
  • 2004 TOYOTA MATRIX
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
Clutch engages does 1 or 2 revolutions and disengages then does it again and again about 1-2 minutes apart. Had the system charged thinking it was low but it still does it and there is no cool air. Wife's car ! Need some advice !
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Saturday, September 22nd, 2018 AT 1:35 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check items in pic use a like relay in under hood fuse box to test relays or go to how to repair section on site here under electrical. If still doing it if relays ok then have it scanned for codes by a local pro
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Saturday, September 22nd, 2018 AT 1:35 PM (Merged)

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