AC works, but will not turn on/off inside car

[maxima278]

I have a 96 240SX SE originally automatic car that because of electrical fire, I put an entire engine, manual transmission, and wiring harness (from ECU all the way around the headlights and into the steering column). Most wires and connectors matched up, a few did not, and I really do not know the relevency behind the ones that didn't. I've been driving the car with very little problems and most everything seems to be in good working order. But, I did not attempt to use the AC until today when I had my father in law vaccuum it and charge it for me. Afterwards, when we mashed the AC button on the dash, the engine would go into fast idle, but the compressor would not turn on. After jumping the relay in the box under the hood, we were able to get it to come on, and I drove it home with the ac on, blowing good cold air, better than my maxima even. Just can't turn it on and off like that, and leaving it jumpered would surely drain the battery. I know there is a safety switch that will not allow it to come on if it is low on freon, but we did put 3 twelve oz cans in it and jumpering the connector that goes into the receiver dryer cannister did not seem to help either. Is there anything I can do to fix this problem without compromising the safety device? If I run out of freon I don't want to be able to kill the compressor. Is 3 cans not enough freon? Am I screwed? Should I just add a toggle switch and risk it? (would rather not) thanks

[NISTECH]

something is not connected, If the engine idle bumps up it means the ECM is sending a signal to turn on the A/C compressor , its just not happening cause something is not right. You need the system to cycle and the way you have it jumped it cant. You would be risking blowing off your freon in high temp/pressure conditions or the system icing in low temp/pressure conditions. I would start searching for what those additional connectors are for.

BTW.3 12 oz cans is 2 and 1/4 pounds of freon I dont think the 96 holds that much freon I think is more like 1 and 1/2 pounds.

[maxima278]

We may not have used all the freon we had, I just know that I bought that much and we filled it up. Do you know where I can find some wiring diagrams? If I don't find the correct wires, could you instruct me on running new ones? I will not run the ac in its current condition, I'm only barely smart enough to know that, if all else fails I'll take the car to a mechanic.thanksJames

[s13sr20chris]

did you try swapping the relay with another of the same color? test the relay terminals for power and ground. if the problem turns up on the control side of the relay you could always cut the wire at the ecm and the relay and run another. thats if you dont feel like finding the open.

[maxima278]

yeah I tried a different relay in the slot. apparently I have power going from the 'hot in' and 'hot out' side, but not on the other two terminals in the relay that tell the ac to cut on and off. where is the ecm located? what does ecm stand for? please use laymans terms as I am rather dense.thanks

[NISTECH]

how exactly did you check for power in the relay socket? you never want to use a test light in a computer controlled socket.ECM stands for Engine Control Module.

[maxima278]

on the control side I have a blue wire with an orange stripe, and a green wire with a yellow stripe. the green and yellow I traced to the receiver dryer, but where does the blue and orange one go? I found two blue and orange on the back of the control unit for the ac/heater blower on the dash, but I don't know if either one is it. is there a difference from 95-96 in what controls the ac? remember my dash wiring is all 96 and under the hood is all 95. I already know that the heater hoses are different. the 95 has a valve with a cable that runs under the dash and the 96 has nowhere for that cable to go. (don't know if that is relevent here but it seems suspicious). Just seems like whatever tells the ac to cycle on and off must be where my problem lies. do you think I am onto something?

[NISTECH]

The engine control module tells the A/C to turn on and off.

[NISTECH]

here ya go

[NISTECH]

#2

[NISTECH]

#3

[NISTECH]

last one needed for operational diag

[maxima278]

I'm gonna try to get my dad to help me with this tommorrow. I can only slightly understand wiring diagrams. My guess is that there is probably nothing wrong with the ecu/ecm itself (if there was then I would guess that it would not send the signal to the engine to make it idle faster), and if it was the receiver/dryer then it would seem I should have been able to jumper it.

Looking at the second diagram you gave me, if I am looking at it right, then could it be the iacv ficd solenoid valve or the ambient temperature switch?

I think I'm getting desparate, or I've fried my brain. cant stop thinking there is something different under the dash from 95 to 96

shoulda gotta 96 parts car. It was 400 bucks what could I say?thank you for your patience

[NISTECH]

operation explained

[maxima278]

just to give you an update, on the connector that goes into the receiver dryer, I tried to connect the corresponding wires using gym clips. the orange/black connected to black made the electric fan come on. First time I think it has ever come on. connecting the green/yellow to the black purple does nothing

[NISTECH]

That tells me the ECM isnt turning on the A/C Which means the idle shouldnt be jumping up. Question: You didnt jump any of the wires in that relay a little up from that switch did you?

[maxima278]

you mean the ac relay above the starter relay? It is not currently jumpered, no. that would make the ac come on all the time. Do you think that black/ purple wire goes all the way to where it should go?

[maxima278]

sounds to me like the ecm is sending the message but it is not getting through the black purple wire

[NISTECH]

If you jumped the wrong terminals in that relay socket you could fry the ECM driver that turns on your A/C. Did you jump any of the other terminals in that realy socket at anytime during your checking?

[maxima278]

shoot. I could have done that. I have a relay that I converted to a continuous circuit connector that I have in place of the starter relay so that the car will start, and I used that in place of the relay. Sounds like I made this worse. The ECM driver that tells the ac to come on, is it the same driver that tells the engine to idle fast?

Is the ECM the same thing as the ECU? that is what I am assuming... on the passenger side by your right foot? If so, I have the one from my 96 auto, it has a different part number on it though, should it work just the same?

[NISTECH]

yes ECM and ECU mean the same thing, I dont know if terminal arrangement from yr to yr is the same though.

[maxima278]

if I give up on this and take it to my mechanic how much do you think it will cost me to get this pain in the rear resolved?

[NISTECH]

This I dont know as it all depends on the area your in and the shop rates. I do have a 95 and 96 service manual on my comp and can look at the comparisions later and try to determine if pin arrangements are the same, this will take some time though.

[NISTECH]

They are different, mainly due to obdII they have a ton more sensors then the 95 ecm , but also I found the A/C is controlled slightly different between the 2 yrs. since you swapped some stuff between the 2 modles what all did you swap. The thing I noticed in the diagrams is the 96 uses all the same pin terminals as the 95 but the 96 uses additional terminals to satisfy OBDII requirements. So I am under the impression the 2 ECM's are the same just that they have different programming so they wont throw codes. As far as AC goes it has a one of the ECM terminals swapped to a different pin, but the ecm seams to be in more control of the A/C system then the earlier model.

[maxima278]

I guess I just wanted to get a feel for whether or not a shop could do the work or if they would just look at me like I was nuts for basterdizing a car the way I did by combining the two year models.

I haven't taken apart the panel where my ecu is yet, (I sort of have kid duty right now) but I guess that black purple should be one of the ones coming out of the ecu, right? So if I cut into that wire, and run one wire straight out of the car, over the fender and into where it goes into the receiver/dryer then if the ecu is ok, then there should be no reason why the AC doesn't come on, right? Unless I fried it of course. In which case do I need a whole new one or can a shop fix it?

whenever you get that info on the ecus I would appreciate it.

I'm really sorry if I have caused you any trouble with all this. Please let me know if I can return the favor somehow. I have really appreciated your help.

[NISTECH]

I gave you the info on the ECU's in my last post. A shop can not fix the internal portion of the ECU.

[maxima278]

sorry, I didn't see that post before I posted. I did not think anyone could fix it, just wanted to be sure. Anyway, I replaced just about every last thing under the hood. It was pretty much all burned up to the firewall, and then just a few inches past where the fuse/relay box had been. The wiring I put in started at the ecu and went into the engine bay and all the way around and stopped at the fuse box on the drivers side, some various connectors there and went on into the steering column. The rest of the dash was untouched. I will try the other ecm tommorrow. Once again thanks for all you doJames

I do still have the 95 car if I need anything from the dash.

[NISTECH]

hold up you say you used the ecm harness?? which car are you fixing? the 96 or the 95? there is one crucial wire in the harness for the ac that is swapped in the ecm connector between the 2 yrs.

[NISTECH]

swap the ecm into this car. and recheck it.

[maxima278]

96 car being fixed. 95 engine, entire wiring harness, ecu, from 95 parts car. the ecu that i have leftover came out of the 96.