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AC/heater control Fuse keeps blowing

 
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Old 08-25-2014, 11:48 AM
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AC/heater control Fuse keeps blowing

My 90 2.0 SI is blowing fuse # 18. This is a 10A fuse for the heater/AC control unit....blown fuse = no power = no AC and in TX @ this time of years is not COOL!

I left the house this morning and the Fuse was blown, replaced it, made it about 15 miles, blown again, replaced fuse again, and before I got out the parking lot it had blown.

Any ideas on what to check or could be causing the issue?
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Old 08-25-2014, 12:41 PM
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Re: AC/heater control Fuse keeps blowing

I feel your pain! I am in Houston and it was 100F yesterday...

SO... This is a diagram of what all Fuse 18 goes to:

HeaterControls_zps5a0d8ff4.jpg Photo by tonemeister6t9 | Photobucket

Rear window defogger relay
Heater Control Motors
A/C Compressor Clutch
A/C Compressor Control Unit

You should buy a box of 10A Fuses, and See if you can disconnect all 4 of these components. If you just turn the A/C off by pressing the A/C button then essentially you have disconnected the Compressor. Then, install the new fuse, and reconnect the components one by one to see which one blows the fuse. Not sure how easy it is to get to the A/C and Heater Control Unit, but it is right behind the ash tray/radio console.

If you haven't already, download the "Prelude Bible"... This thing is awesome to have. Here's the link:

pdftown.com_prelude3g

Try leaving the A/C Switch
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Old 08-25-2014, 09:12 PM
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Re: AC/heater control Fuse keeps blowing

So far I have pulled the rear defrost relay and disconnected one of the controls (i still have to disconnect the other one). I also pulled both AC relays and measured resistance both were about 112 ohms between 2 pins then reinstalled. I then tried a new fuse and all was good until I pushed the AC on switch and when I hear the clutch click the fuse blows.
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Old 08-25-2014, 10:51 PM
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Re: AC/heater control Fuse keeps blowing

Sounds like you found the problem.
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Old 08-25-2014, 11:26 PM
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Re: AC/heater control Fuse keeps blowing

Quote:
Originally Posted by luzer View Post
Sounds like you found the problem.
I need a bigger fuse. . :-)

Definitely something with the AC Compressor ON Circuit. I need to look at the wiring diagram unless someone on this forum has recommendations. The clutch does turn by hand.

I cant find the connector for the recirc control motor (this is the one right by the blower).

Last edited by hienz57; 08-26-2014 at 12:29 AM.
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Old 08-26-2014, 10:30 AM
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Re: AC/heater control Fuse keeps blowing

Quote:
Originally Posted by luzer View Post
Sounds like you found the problem.


Quote:
Originally Posted by hienz57 View Post
I need a bigger fuse. . :-)
I SURE hope you are kidding!
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Old 08-26-2014, 10:52 AM
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Re: AC/heater control Fuse keeps blowing

Yes I was kidding about the fuse.

I am going to test a few other things of the AC ON circuit to see if I can pin point the faulty part. Hoping it isn't the electronic parts of the compressor clutch since it is an expensive part and a pain in the a$$ to replace.
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Old 08-27-2014, 12:39 AM
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Re: AC/heater control Fuse keeps blowing

I'm leaning towards the issue being a faulty compressor clutch. I check the resistance between compressor control unit 12 pin connector and GND an it measure 6 ohms, the manual desired results says should be appox. 4 ohms...so 2 ohms higher than desired. Any way to test the thermal protector that is part of the clutch?

Any chance this could induced by a faulty compressor control unit?
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Old 08-27-2014, 01:00 PM
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Re: AC/heater control Fuse keeps blowing

Ok, here's what I'm thinking...

NOT sure if you tried this already, but try disconnecting the clutch connector and then turn on the A/C to see if the fuse still blows... If the clutch is disconnected from the circuit, and it is bad, it couldn't cause the fuse to blow. If the fuse DOES blow, then you either have a bad control unit, or one of the other components that is connected to it is causing the issue.

Crazy question... Did you zero out your meter leads before taking that reading? And, Are you able to put the meter leads on the pins "Real good". 2 ohms isn't that much of a difference and you could get that variance just by not touching the leads to the pins real well, especially if they are dirty...

Now, if you were reading 0 ohms and supposed to read 4 ohms, THAT is a big difference... it would mean that your clutch is shorted internally... And I could see that causing a fuse to blow.

And... if it was reading more like 10+ ohms you might have an issue or at least be enough to matter, especially if you had an electronic A/C circuit that measure the "precise" impedance value of your clutch coil, it might cause a fault light... But seriously doubt that would cause a fuse to blow.
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Last edited by tonemeister69; 08-27-2014 at 01:03 PM.
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Old 08-27-2014, 02:02 PM
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Re: AC/heater control Fuse keeps blowing

Quote:
Originally Posted by tonemeister69 View Post
Ok, here's what I'm thinking...

NOT sure if you tried this already, but try disconnecting the clutch connector and then turn on the A/C to see if the fuse still blows... If the clutch is disconnected from the circuit, and it is bad, it couldn't cause the fuse to blow. If the fuse DOES blow, then you either have a bad control unit, or one of the other components that is connected to it is causing the issue.

Crazy question... Did you zero out your meter leads before taking that reading? And, Are you able to put the meter leads on the pins "Real good". 2 ohms isn't that much of a difference and you could get that variance just by not touching the leads to the pins real well, especially if they are dirty...

Now, if you were reading 0 ohms and supposed to read 4 ohms, THAT is a big difference... it would mean that your clutch is shorted internally... And I could see that causing a fuse to blow.

And... if it was reading more like 10+ ohms you might have an issue or at least be enough to matter, especially if you had an electronic A/C circuit that measure the "precise" impedance value of your clutch coil, it might cause a fault light... But seriously doubt that would cause a fuse to blow.
Good suggestion Tony. And that wasn't a crazy question. It's a common mistake that people make when ohming out low resistance circuits.

Quote:
Originally Posted by hienz57 View Post
I'm leaning towards the issue being a faulty compressor clutch. I check the resistance between compressor control unit 12 pin connector and GND an it measure 6 ohms, the manual desired results says should be appox. 4 ohms...so 2 ohms higher than desired. Any way to test the thermal protector that is part of the clutch?

Any chance this could induced by a faulty compressor control unit?
Higher than "normal" resistance will not cause a fuse to blow. Higher resistance actually reduces the amount of current that will flow through a circuit. Fuses blow when they are passing more current than they are rated for.

Try what tonemeister69 suggested.
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Old 08-27-2014, 04:51 PM
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Re: AC/heater control Fuse keeps blowing

Quote:
Originally Posted by tonemeister69 View Post
Ok, here's what I'm thinking...

NOT sure if you tried this already, but try disconnecting the clutch connector
and then turn on the A/C to see if the fuse still blows... If the clutch is disconnected from the circuit, and it is bad, it couldn't cause the fuse to blow. If the fuse DOES blow, then you either have a bad control unit, or one of the other components that is connected to it is causing the issue.

Crazy question... Did you zero out your meter leads before taking that reading? And, Are you able to put the meter leads on the pins "Real good". 2 ohms isn't that much of a difference and you could get that variance just by not touching the leads to the pins real well, especially if they are dirty...

Now, if you were reading 0 ohms and supposed to read 4 ohms, THAT is a big difference... it would mean that your clutch is shorted internally... And I could see that causing a fuse to blow.

And... if it was reading more like 10+ ohms you might have an issue or at least be enough to matter, especially if you had an electronic A/C circuit that measure the "precise" impedance value of your clutch coil, it might cause a fault light... But seriously doubt that would cause a fuse to blow.
Disconnecting the clutch connector was my next step…if I can reach the connector. Otherwise I pull relay B (last relay before the compressor clutch) and see what happens. The relay is easy to get to.

I didn’t zero out the meter ( have to check my meter on how to do this), was able to contact the pins real well, and understand that higher resistance would mean less current.

When I took the resistance measurement, I followed the instructions in the 90 prelude update service manual sec 15-9 to check resistance to GND on the compressor control units 12 pin connector (pin 8 brown wire) with the ign, blower, & a/c switches ON (when I say ign switch on the key was forward but vehicle not running) . An observation when the ign switch was OFF was that the resistance between compressor control units 12 pin connector (pin 8 brown wire) & GND was 0, but nothing I saw in the manual mentions readings on this pin when OFF.

I have been doing this late at night and in the dark after my 2 yr old is sleeping so I haven’t been debugging as fast I would like.

Last edited by hienz57; 08-27-2014 at 07:03 PM.
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Old 08-27-2014, 11:58 PM
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Re: AC/heater control Fuse keeps blowing

Update:

Pulled the relay b which removes the compressor and no blown fuse.

Using the compressor control unit connector I jumped the power to the relays pins 10 and 11 to pin 12 while the key was forward but car not running and then when the car was running. This takes the ac control module out of the equation since it was no longer connected and turns on the relays. The relays click as they should and when the car is stated....bet you can guess what happens....fuse blows.

Checking AC Compressor pins:
There is continuity between thermal protector pins (pins 1&3) which is what the manual days it should be.

The one thing that throws me off is the trouble shooting for the pins on the compressor pick up sensor. The pick up sensor doesn't have continuity between pins 2&4, which one page says it should have, but measure resistance at 0.55 ohms, which is what another page says is in range.

Seems like from the testing done tonightit is the AC clutch.
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Old 09-02-2014, 06:35 AM
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Re: AC/heater control Fuse keeps blowing

Quote:
Originally Posted by hienz57 View Post
...Seems like from the testing done tonightit is the AC clutch.
Which means time for a new compressor.
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Old 09-06-2014, 04:50 PM
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Re: AC/heater control Fuse keeps blowing

Installed a remanufactured compressor from AutoZone today. I can't get the compressor to stay on, the red light on the AC switch comes on. I have checked the belt tension and still no luck. It wont stay on long enough to charge the system. I did get about 1 can of 134a in.

What else could be causing this and is there anyway to bypass it?

Last edited by hienz57; 09-06-2014 at 04:52 PM.
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Old 09-06-2014, 10:57 PM
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Re: AC/heater control Fuse keeps blowing

Did you pull a vacuum on the system before you charged it?
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Old 09-06-2014, 11:51 PM
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Re: AC/heater control Fuse keeps blowing

Quote:
Originally Posted by luzer View Post
Did you pull a vacuum on the system before you charged it?
Yes, pulled vac 15 min, tested for leaks 15 min, and pulled some more vac 15min. I then attached the 134a, bled the line, then opened the low side, let it take a little in, then started the car, AC on. The clutch kicks on but only for a few seconds, then kicks off, and the red light on the AC button is on. Push the button off and on, same results.

Probing around on the new AC comp connector, the GRN and WHT wire doesn't measure resistance (pick-up sensor). Old AC comp does measure 542 ohms.

Is the pick-up sensor what tells the ac control unit the RPMs of the compressor? If so, a faulty PU sensor would explain my issue. If this is the case, Autozone is going to pay (angry and frustrated).
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Old 09-09-2014, 03:36 PM
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Re: AC/heater control Fuse keeps blowing

Quote:
Originally Posted by hienz57 View Post
Installed a remanufactured compressor from AutoZone today. I can't get the compressor to stay on, the red light on the AC switch comes on. I have checked the belt tension and still no luck. It wont stay on long enough to charge the system. I did get about 1 can of 134a in.

What else could be causing this and is there anyway to bypass it?
Quote:
Originally Posted by luzer View Post
Did you pull a vacuum on the system before you charged it?
Quote:
Originally Posted by hienz57 View Post
Yes, pulled vac 15 min, tested for leaks 15 min, and pulled some more vac 15min. I then attached the 134a, bled the line, then opened the low side, let it take a little in, then started the car, AC on. The clutch kicks on but only for a few seconds, then kicks off, and the red light on the AC button is on. Push the button off and on, same results.

Probing around on the new AC comp connector, the GRN and WHT wire doesn't measure resistance (pick-up sensor). Old AC comp does measure 542 ohms.

Is the pick-up sensor what tells the ac control unit the RPMs of the compressor? If so, a faulty PU sensor would explain my issue. If this is the case, Autozone is going to pay (angry and frustrated).
Only 1 can of R134? I think the system takes moe than that. The compressor has a low pressure switch that will keep the clutch from kicking on if there isn't enough freon in the system. It is probably turning on when you hit the button, and then kicking right back off.

Did you replace the Dryer or the Orifice tube? Most places won't honor the compressor warranty if those 2 items aren't replaced at the same time as the compressor.

And did you add oil to the system?

How long ago did you do the R134 conversion?

Just going through the usual checklist.

Also, I know it sounds anal, but I don't think that 30 minutes is enough time to pull a full vacuum on any system... If you have to do it again, I'd at least pull a vacuum for an hour. And get a bottle of the dye so you can make sure you don't have any leaks.
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Old 09-09-2014, 03:41 PM
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Re: AC/heater control Fuse keeps blowing

I forgot to ask/say... I take it that your fuse isn't blowing anymore though is it?
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