Ok so this is totally out of my league and I'm wondering if the mechanic I am dealing with is trying to get over on me.
The A/C compressor clutch was not engaging so I took it to the mechanic shop I have been doing business with for years. They determined the problem to be a bad AC clutch relay wire. They are saying that to fix it I will need a new wire (obviously) and a new ECM. I cannot get a straight answer as to why the ECM is needed. Everything else on the car works fine. Does this sound legit to you guys? Diagram showing the defective wire.

 

So long as the ECM was receiving the 'enable' command from the source it's maybe likely. Is this a C60 (manual) or C68 (ATC) system?

 

It's an ATC system. Also it is converted over to the R134. The car is a 1990 L98 automatic trans. If it does need an ECM is this because something got damaged in it when the wire broke?

 

I'd think a 'discussion' regarding programmer operation legitimate. A busted/bent pin(s) or connector to the ECM maybe. You're the guy that's gotten apparently good service previously. I wouldn't think he's any real good reason to 'get over on you' with a part.

How much have you spent for diagnostics thus far?

 

So far nothing. They are good about diagnosing without charging. Although I'm sure they make up for it during the repair. They have worked on all my vehicles over the years and I had no complaints. This particular mechanic is fairly new there so I am not very familiar with him. I'm just a bit perplexed as to why he cannot give me an explanation. The repair isn't horribly expensive (approx. $400.00).
The biggest red flag for me was when he suggested a "cheaper" fix. Said he could run a wire to a toggle switch installed on the dash and when I wanted AC I could just flip the switch. I guess maybe this would work but I wouldn't think a reputable repair center would want to suggest this type of fix. Maybe a conversation with the owner is in order. I don't want to get the mechanic in trouble but I don't want to receive half a** work either.

 

Do you have the FSM for your car? If yes maybe you supply the tech with it for diagnostics of compressor control. It could be an interesting read maybe for both you and he. See 8A-67-5 for what you mention is happening. Lots to check.

 

Thanks for that info! I do have the FSM on cd. I'll dig it out and take a look.

Thanks Again!

 

How the circuit works and possible direction.

12 volts is applied to pin 2 of the clutch relay and the return is thru pin 5 to a ground to turn on the relay. In this case the ECM makes the connection to ground. So for starters, make a voltage check at pin 5 of the relay and pin A13 of the ECM and see if there are the same reading. If the voltage is high (12vdc) on both ends then the ECM is not closing the return circuit for the relay to be energized. If the reading are not the same then the wire is open somewhere or a bad pin connection. You can also make a resistive measurement across this wire with power off.

If the voltage reading at pin A13 of the ECM is 12 volts, then you need to measure pin B15 of the ECM and see what that reading is. If it is 12 volts, then the ECM is not responding to that signal closing the ground for the relay. In that case either the ECM is bad, or there could be another signal from another source like a high pressure sensor on the high side of the A/C line may not be measuring correctly which might inhibit the ECM to go into A/C mode (or something similar).

If the voltage reading at B15 is 0 volts, then the ECM has not received the signal to close the A/C relay by making Pin A13 go to ground thus closing the relay. In this case you would have to work back to the source (from B15) of the 12 volts to be applied to find out why you are losing it when the A/C is requested.

Without knowing these few pieces of information, you are taking a big guess to replace a ECM. If it does look defective, then you go for it.

 

You need a scanner to see if ecm is commanding ac on. There are inputs that will disable ac.