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C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Have to jump ground to relay to make it

 
Old 07-13-2019, 10:56 AM
  #21  
radar502
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Update : Well I went to this shop and they pulled out what looked like big case full of wires big hand held OBD checkers deals and after 1-1/2 HRS of checking and looking and bushing bottoms . Well said the signal was not gong to the compressor . I knew that before I left my house . I am going to do some checking myself and see if I can figure were is or were is not the power or the signal is not getting to, if I can't find the problem( not being a ELE . guy is not easy to do) .. send the head and the controller and the ECM for a test .. That's were I'm at .... Right now I am riding with the jumper on the A/C , blowing nice cold air .. Thanks for all who tried to help ,will use the info to try to track down the NO signal ..
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Old 07-13-2019, 04:37 PM
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Originally Posted by pcolt94 View Post
Lots of items and things have to happen to turn the compressor on.
The ECM is the ground return for the compressor relay. So all the inputs to the ECM have to be there the for it to energize the relay.

The cycling switch has to be closed.
The pressure switch sensor on the high side line has to be operational and put out a voltage.
The A/C control head has to put out an A/C request (5 volts) to the ECM

These basic items are required in addition to the control head and ECM working properly.
Having electrical diagrams, meters and a knowledge of electronic will help.

The most simplest items to check is the cycling switch. See if it checks closed.

Hard to say where to start. Biggest problem is getting to points to measure and check.
Sorry to say you're probably not going to fix this checking for codes. But you can check just to see if there is a pressure sensor code.

Check all ECM fuses.
A tech 1 can energize the compressor clutch. But I donít know if it will or won't in your case. And if it does not energize the clutch you still donít know any more than you did initially, it's not a crystal ball.
The tech 1 did not energize the clutch and yep I know no more that I did ,going to pull out the head controls and start checking . The first thing is well the fuses but the Tech said all good ?? next the 5vs going to the controller if got power then the power going to the ECM .. if I got power to the ECM will send it to Batee and have it checked ..The only way I know how to do it.. Thanks .. Well the Tech 1 guy said if I got power coming out of the EMC probably shorted wire going to the relay .. Well , I might start there and work back??? or might buy a $155,000 ZR-1 .. NO I'll check the wires .. A friend just got one from the museum nice for sure .. First thing he had to do was go buy $6,000 worth of tires and wheels he got the track pack ??? I'll just work on my A/C ..
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Old 07-13-2019, 05:17 PM
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What led you to believe you ran out of freon? (when it stopped working).
I kind of suspect you might not have a freon problem (but just a hunch).

I have a 94 with a PCM and you have a 93 with a ECM. Very similar but different. Codes DTC 66 and 67 (in module 4) are for the high pressure sensor (3 wire sensor on high side pipe). If the ECM/PCM does not see a pressure change in 10 seconds, the firmware will inhibit the compressor from coming on. This inhibit will not reset until you turn the key to off for about 15 seconds or so and then you are good to go again. This prevents the compressor from running with no freon in the system. (just something to keep in mind).

But even with very little freon in the system the cycling switch should be closed and the compressor should try to start if all electronics are working.

One simple check you can do is to unplug the cycling switch and connect a volt meter to the DK/BLUE wire. Then turn key to ON (no need to start) & note the reading, should be near 0.0. Then press recirc AC (AC on) and note the reading, it should be around 10 vdc. (If plugged in and loaded would read 5 volts). This would indicate the control head and programmer is working

If that’s OK, you said you grounded the return wire of the AC relay and the compressor started which means the compressor and relay is OK. That would leave the ECM not closing the AC relay for some reason.

Make sure there are no broken wires at the 3 wire high pressure sensor. I personally would back probe the RED/BLACK wire to see if there was at least 1.0 or more vdc there. If that was good, then the ECM might be the problem.

Of course any broken wire or bad connection could also be the problem

Last edited by pcolt94; 07-13-2019 at 05:19 PM.
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Old 07-13-2019, 10:01 PM
  #24  
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Well ,The A/C air starting getting warm so I checked it and no Freon in the system had leaking compressor I have a leek tester . I put some Freon back in and checked yep compressor leaking ,replaced everything all new parts . The sys has Freon in for sure when I jump it is very cold air and all the controls work fine and I put a gauge on it no leaks . I have NO codes .Just had it checked with a tech -1 nothing showed up. The pressure sensor has a new pig tail. Thanks for the info and I will starting Mon. running test , until now have been checking and replacing pig tales and waiting for new switches to come in now all is new under the hood ,time for testing if all is good outside then I say its time to start checking the controller ECT. Thanks ..
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