A/C diagnostic not going well.......
Thread Starter
Advanced
Joined: Apr 2009
Posts: 62
Likes: 10
From: Columbus, Oh
A/C diagnostic not going well.......
Hi there. New owner here, 1 month with a nice 1990 silver metallic GT, 77K, no cats and an authority chip. I have put 250 entertaining miles on so far.
Taken care of the Toothed belt alarm (loose tensioner), misc. leaks, new tires (direzza star spec) and misc. check outs. Now on to bigger stuff. Like non operational A/C.
Using the Dr. Bob/L. Ott/Wally write ups I determined the blue relay in the control head was bad. No power at all to freeze switch.
Pulled the head unit, took the covers off and could hear something rattling in the little blue relay. Pried the relay cover off and 1 of the arms is broke/burned off. So onto Dr. Bob's relay repair. Hooked everything back up. Still no compressor clutch. Damm!
So re-performed the following tests:
Freeze switch. pull back the 2 leads, but not remove completely from the switch. probe on 1 lead and probe to ground, get 12 volts. Probe on other lead and to ground, get 12 volts. Now I am confused, but a little happy, looks like I got the relay going right. But still no compressor clutch.
Pulled leads off of freeze switch, hooked jumper wire between..... nothing.
Pulled low pressure plug off of switch and installed jumper wire to plug....... nothing.
Pulled the red connector to the compressor. Jumped it to the passenger fender Jumper point, Compressor clutch kicked on no trouble.
Any additional advice would be helpful. Thanks.
Doug
Taken care of the Toothed belt alarm (loose tensioner), misc. leaks, new tires (direzza star spec) and misc. check outs. Now on to bigger stuff. Like non operational A/C.
Using the Dr. Bob/L. Ott/Wally write ups I determined the blue relay in the control head was bad. No power at all to freeze switch.
Pulled the head unit, took the covers off and could hear something rattling in the little blue relay. Pried the relay cover off and 1 of the arms is broke/burned off. So onto Dr. Bob's relay repair. Hooked everything back up. Still no compressor clutch. Damm!
So re-performed the following tests:
Freeze switch. pull back the 2 leads, but not remove completely from the switch. probe on 1 lead and probe to ground, get 12 volts. Probe on other lead and to ground, get 12 volts. Now I am confused, but a little happy, looks like I got the relay going right. But still no compressor clutch.
Pulled leads off of freeze switch, hooked jumper wire between..... nothing.
Pulled low pressure plug off of switch and installed jumper wire to plug....... nothing.
Pulled the red connector to the compressor. Jumped it to the passenger fender Jumper point, Compressor clutch kicked on no trouble.
Any additional advice would be helpful. Thanks.
Doug
Thread Starter
Advanced
Joined: Apr 2009
Posts: 62
Likes: 10
From: Columbus, Oh
I did a static check/partial fill as the compressor is not running. Checked at 35lbs.
Even if system is low, jumping the low pressure switch should have fired the compressor to check for accurate running pressure.
Suggestions?
Even if system is low, jumping the low pressure switch should have fired the compressor to check for accurate running pressure.
Suggestions?
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Mar 2002
Posts: 13,660
Likes: 621
From: Phoenix AZ
Be methodical...
Test the pressure switch in circuit - do you see 12v on both terminals with AC engaged? if you have 12v on only 1 terminal then you likely have insufficent freon charge. If you have 0V on both its likely a wiring issue from the freeze switch to the pressure switch, if you have 12v on both it seems like a wiring issue between the pressure switch and the clutch. Test this wire off the clutch with a voltmeter - does it go to 12v? when connected to the clutch what voltage do you see on that wire?
Alan
Test the pressure switch in circuit - do you see 12v on both terminals with AC engaged? if you have 12v on only 1 terminal then you likely have insufficent freon charge. If you have 0V on both its likely a wiring issue from the freeze switch to the pressure switch, if you have 12v on both it seems like a wiring issue between the pressure switch and the clutch. Test this wire off the clutch with a voltmeter - does it go to 12v? when connected to the clutch what voltage do you see on that wire?
Alan
Thread Starter
Advanced
Joined: Apr 2009
Posts: 62
Likes: 10
From: Columbus, Oh
DUH!!!
Thanks Alan. Sometimes the simple things stare you right in the face. Went and checked the voltage to the low pressure switch and it is less than 1 volt. So need to hunt down the leakage or run new wiring, which I am sure is going to be no fun.
Ah, why did I not buy that cute little mga instead. Probably 7 or 8 wires on the entire car....
Thanks again for taking a tired fustrated guy and pointing him in the right direction.
Thanks Alan. Sometimes the simple things stare you right in the face. Went and checked the voltage to the low pressure switch and it is less than 1 volt. So need to hunt down the leakage or run new wiring, which I am sure is going to be no fun.
Ah, why did I not buy that cute little mga instead. Probably 7 or 8 wires on the entire car....
Thanks again for taking a tired fustrated guy and pointing him in the right direction.
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Oct 2001
Posts: 20,506
Likes: 565
From: Bend, Oregon
VFR4--
Get a copy of the wiring diagrams if you don't have them already.
You are good on the testing so far. The pressure switch jumper (make sure you are jumpering the switch connector and not the pressure sensor...) eliminates the possibility of low freon level preventing compressor start. If you see 12V at the pressure switch jumper but the compressor still doesn't run, look next at the 14 piin connector near the jump-start post, where the front-of-engine harness connects to the car. If the connections are corroded, obviously you'll nbeed to freshen them. That FOE harness runs from the connector towards the rear of the car over the cam belt cover, goes through a clamp that attches to the front pass side engine lift hook, under the cam belt cover and forward, and across the front of the engine. Routing is BEHIND the oil dipstick tube, towards the middle lift bracket. Right by the dipdtick tube, the harness wire for the compressorr routes out of the bundle for the connection to the captive compressor wire. That's the circuit.
Get a copy of the wiring diagrams if you don't have them already.
You are good on the testing so far. The pressure switch jumper (make sure you are jumpering the switch connector and not the pressure sensor...) eliminates the possibility of low freon level preventing compressor start. If you see 12V at the pressure switch jumper but the compressor still doesn't run, look next at the 14 piin connector near the jump-start post, where the front-of-engine harness connects to the car. If the connections are corroded, obviously you'll nbeed to freshen them. That FOE harness runs from the connector towards the rear of the car over the cam belt cover, goes through a clamp that attches to the front pass side engine lift hook, under the cam belt cover and forward, and across the front of the engine. Routing is BEHIND the oil dipstick tube, towards the middle lift bracket. Right by the dipdtick tube, the harness wire for the compressorr routes out of the bundle for the connection to the captive compressor wire. That's the circuit.
Thread Starter
Advanced
Joined: Apr 2009
Posts: 62
Likes: 10
From: Columbus, Oh
THanks Dr. Bob,
Great help with your relay replacement write up.
At this time I am getting less than 1 volt at the pressure switch. I am getting 12 volts @ both leads on the freeze switch after relay replacment.
Got hold of a local 928 owner club guy that lives just up the street and he is going to help me trace out the no power to the pressure switch tonight.
I have a full set of WSM's that came with the car, for elec. schematics.
THanks again
Great help with your relay replacement write up.
At this time I am getting less than 1 volt at the pressure switch. I am getting 12 volts @ both leads on the freeze switch after relay replacment.
Got hold of a local 928 owner club guy that lives just up the street and he is going to help me trace out the no power to the pressure switch tonight.
I have a full set of WSM's that came with the car, for elec. schematics.
THanks again
Trending Topics
Rennlist Member
Rennlist Site Sponsor
Joined: Jun 2001
Posts: 6,469
Likes: 13
From: Ball Ground, GA
Doug,
From the antifreeze switch, the power enters the Central Electric Panel on G21. One lead runs directly to E11, and from there to the high/low pressure switch.
Checking the voltage at E11 will probably tell you instantly whether or not the problem is inside the Central Electric Panel. If you have 12 vdc at E11, the problem is almost certainly in the wire from there to the high/low pressure switch.
Inside the Central Electric Panel, one lead runs from G21 to the suppressor, Relay XXI. This is NOT a relay, but is a suppressor to control the electrical kickback from the compressor clutch coil. If the voltage is low at E11, it might be possible for this suppressor to have failed, and it might be worthwhile pulling it to see if the voltage at the pressure switch goes up.
Another lead T's off of the compressor clutch power lead inside the Central Electric Panel and runs to W24, and from there to the LH ECU. If the voltage is low at E11, you could also pull Plug W off and see if the voltage increases. We certainly hope not, because that possibly shows a problem inside the LH ECU!
From the antifreeze switch, the power enters the Central Electric Panel on G21. One lead runs directly to E11, and from there to the high/low pressure switch.
Checking the voltage at E11 will probably tell you instantly whether or not the problem is inside the Central Electric Panel. If you have 12 vdc at E11, the problem is almost certainly in the wire from there to the high/low pressure switch.
Inside the Central Electric Panel, one lead runs from G21 to the suppressor, Relay XXI. This is NOT a relay, but is a suppressor to control the electrical kickback from the compressor clutch coil. If the voltage is low at E11, it might be possible for this suppressor to have failed, and it might be worthwhile pulling it to see if the voltage at the pressure switch goes up.
Another lead T's off of the compressor clutch power lead inside the Central Electric Panel and runs to W24, and from there to the LH ECU. If the voltage is low at E11, you could also pull Plug W off and see if the voltage increases. We certainly hope not, because that possibly shows a problem inside the LH ECU!
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
9 Features and Characteristics That Only Porsche People Understand
Verdad Gallardo
I've Written 500 Rennlist Articles: Here's How Porsche Has Changed Along the Way
Joe Kucinski
10 Most Unnecessary Porsches Ever Built (And Why We Love Them)
Verdad Gallardo
Porsche 911 GT3 S/C vs 718 Spyder RS: 10 Categories, One Winner
Joe Kucinski
This Builder Is Turning Heads With Its Slantnose 911 Creation
Verdad Gallardo
Porsche 911 GT3 Artisan Edition Pays Homage to Japanese Culture
Verdad Gallardo
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
Racer
Joined: Mar 2009
Posts: 496
Likes: 2
From: Flower Mound, TX
Oh, I also wanted to add - MG A's are Lucas electrics, right? If so, you're probably better off where you are.
Instructor
Joined: Jun 2008
Posts: 133
Likes: 1
Hey Doug,
Sorry I don't know much about a/c, but if you are working on the shark, let me know. My a/c also isn't working at this time.
Let me know when you want to look at that rear quarter. I just picked up a new cutting pad for the buffer.
Sorry I don't know much about a/c, but if you are working on the shark, let me know. My a/c also isn't working at this time.
Let me know when you want to look at that rear quarter. I just picked up a new cutting pad for the buffer.
Thread Starter
Advanced
Joined: Apr 2009
Posts: 62
Likes: 10
From: Columbus, Oh
I'm thinking it's just the difference between other people going "Oooh" and "Ha ha" ?
That and the HP factor. I am a speed junky.......
Wally,
Thanks for the additonal tracing info. The "New" WSM electrics are not as easy to read / decipher as the older schematics. Had a local owner with a 79 stop by and point out a couple things to trace. He kept complaing this new stuff was too hard to figure out. Popped the 14 pin connector on the pas. fender, and ran a few traces. Don't have the notes right in front of me, but he was thinking the problem is in the electric panel as well. Praying not the ECU, tho the PO had it rebuilt by sharktuner guy about 4 years ago....
Take another crack at it tonight.
That and the HP factor. I am a speed junky.......
Wally,
Thanks for the additonal tracing info. The "New" WSM electrics are not as easy to read / decipher as the older schematics. Had a local owner with a 79 stop by and point out a couple things to trace. He kept complaing this new stuff was too hard to figure out. Popped the 14 pin connector on the pas. fender, and ran a few traces. Don't have the notes right in front of me, but he was thinking the problem is in the electric panel as well. Praying not the ECU, tho the PO had it rebuilt by sharktuner guy about 4 years ago....
Take another crack at it tonight.