S13 SR20 Swap AC Questions and Comments

[DaveAZ]

1989 SOHC chassis with SR20 swap. Original car had AC. SOHC AC compressor doesn't bolt at all to SR20, nor does Cody Ace make the adapter for it.

(We routinely get temps over 100F, so I don't care if you are a drifter and don't need AC, we do) :)

So: We got the DOHC compressor and Cody's adapter. This compressor however has single point bolt mounting points for the lines. The stock SOHC lines are double bolted and oh so slightly different in size. So I scrounged around for used lines. I also (tried) to order new lines from Courtesy Nissan. "Parts unavailable."

I modified the existing lines so they should fit, but matching green o-rings for a good seal is very tedious.

I do note that the DOHC compressor is a single wire directly from the AC relay circuit to the clutch. There is no pressure switch wired in series with the clutch circuit. Does that sound correct? No pressure switch protection in these S13 DOHC compressors?

The temp sensor that goes into the stock KA lower radiator hose isn't used on the SR20. Should I use the T-stat we are using to run the electric radiator fans? Or separate relay for the condensor fan? (Concerned about amp draw across the relay if running three fans instead of two)

The AC relay is spliced to the correct wire going to pin 106 on the ECU. This is supposed to function as the ground for the AC relay, once the system is turned on. The F3 plug wire from the dash is also ran to correct pin on SR20 ECU. However, when we jump the pressure switches at receiver dryer, the AC relay does not get a ground. We can manually ground it at the ECU and it does energize, so we know we have the correct wire.

Stupid question: Does the engine have to be running for the ECU to provide the ground to the AC relay?

This has been an uphill battle. I would greatly appreciate any solid help or advice from those who have been there, done that with an almost complete rebuild of their systems.

[ultimateirving]

i have a/c in my s13 sr, with a s0hc chassis. but i used dohc components for everything. except for the heater box/assembly in the cabin is stock.

I do have a single wire going to my compressor, i dont know about any a/c relays be cause i just basically got new hoses made to fit my car, took the 240 to an a/c guy and had him vacuum test the system and check to make sure its wired.

[codyace]

Hey Dave:

Operation of the compressor is one thing (as that's ONLY through the AC relay)...and yes you are correct there is not any sort of DoublePressure protection on that side of the house.

HOWEVER, where the Double Pressure switch (the only thing on the dryer) comes into play is how it allows for the air conditioned air, to get pumped/blown into the cabin. While I don't have the SOHC stuff to know 100%, I know from the DOHC aspect of things that the Double Pressure switch acts as the failsafe obviously between the push control unit, and the fan selection switch (essentially if the DP switch is shit, it won't allow you to even cycle the fans on to blow AC, even if the compressor is on and working)

Edit: The above in relation to the KA system (where the ECU has the pin for the ground signal to the AC relay, and the pin for the AC system to turn on in regard to the H/A system)

Edit: I can assure you this though, that once you dive into the actual HVAC system, it's a complex array of circuits to make it actually 'blow cold air'.

[DaveAZ]

the Double Pressure switch acts as the failsafe obviously between the push control unit, and the fan selection switch (essentially if the DP switch is shit, it won't allow you to even cycle the fans on to blow AC, even if the compressor is on and working)

Hi Cody, One of the parts I was actually able to get was the receiver/dryer assy with the new pressure switch. For initital testing, I jumped (shorted) that switch to get the pushbutton for AC to work.

What I can't figure out is what the ECU is doing electrically to allow pin 106 to become the ground for the AC relay. The only way I've gotten the AC relay to work is by manually grounding the wire going to pin 106. If all else fails, I could rig a relay in the car to accomplish that outside of the ECU, but would lose idle-up, and accell cutout.

(Note) Coutesy also sent the wrong HP line from the comp to the cond and since I opened the plastic wrapper to discover this, I can't return that $85 piece. Looks like custom made lines are the only way to go if you want them new.

I do have a single wire going to my compressor, i dont know about any a/c relays be cause i just basically got new hoses made to fit my car, took the 240 to an a/c guy and had him vacuum test the system and check to make sure its wired.

That might have made this all more simple Irving. I worry about putting these lines back together, then getting it tested, and having to disassemble the front end of the car at the AC shop. We're replacing 100% of the components under the hood. No way do I want the AC shop removing the front bumper, lights, and intercooler to get to the fittings on the condensor.

Maybe I am overthinking this, nothing will leak, and everything will work when filled with freon. lol..

[DaveAZ]

Update: Got it working. Yes, the engine must be running for the ECU to give the AC relay a ground. We have AC cutout for accell, and we have idle up.

Cody Ace bracket made mounting a lot easier. I got one of the older/earlier SR20 to S13 DE mounts. No removing of the AC comp. mount nubs was required. Bolted right on. Cody included a belt with the kit, KO 365, but it was too long, and 345 (also used on PS) was too short, but the 355 fit great.

We used all SOHC hoses, which required cutting off half the compressor mounting plate for those two hoses. The low side fits horribly, but surprisingly we got it to seal. Replaced all o-rings with greens, dumped in some PAG100 and a bit over 3 cans of 134 and it gets ice cold.

I am pretty stoked, as it gets well over 100 often here at the river on the AZ side. I can certainly see why those who don't "need" AC get rid of it, lol.

I'm available if anyone has any questions on their S13 SR20 AC system, and Cody has been great answering questions and supplying the mount.

[ultimateirving]

awesome man! glad to hear you got it working. at first it seems like a lot but once you start hookin stuff up. It came together pretty smoothly for me too, and i know what you mean by the hoses barely fitting, im surprised i was able to get it all to seal up at the compressor as well. haha!

[DaveAZ]

awesome man! glad to hear you got it working. at first it seems like a lot but once you start hookin stuff up. It came together pretty smoothly for me too, and i know what you mean by the hoses barely fitting, im surprised i was able to get it all to seal up at the compressor as well. haha!

Thanks! After I posted, I had to rebuild the control box, because the lube on the buttons had dried up.

How are you controlling the condensor fan? Right now, I have it wired to come on any time the AC is turned on. Stock, it was made to go through a "thermo switch" located in the bottom radiator hose on the KA. Something like 180F turn on.

I have twin electric cooling fans and an aftermarket thermo switch to control it via a new relay. That relay is good for 25 amps, and the engine fans are drawing 15. So I think the condensor fan will draw too much for the relay.

What's the fix? Install stock in-line thermo switch, install second relay, or just leave it shorted to run when ever AC is on?

[ultimateirving]

thats where i left off dave, im running stock clutch fan. I dont have any other fans or anything, So far i havent overheated without running an conds fan.

[DaveAZ]

thats where i left off dave, im running stock clutch fan. I dont have any other fans or anything, So far i havent overheated without running an conds fan.

Just the one fan....I never would have expected that answer. Do you also have an intercooler? I assumed the heat within the condensor would be increased due to the intercooler being in front of it, and that the AC system would cycle too much without the fan if it was hot enough.

I'm probably leaning towards running a second fan control relay for the condensor fan. (As long as I went through the hassle of finding another condensor fan)

[ultimateirving]

It did cycle on and off some at stoplights during the summer, but never that long really. I do run an fmic, so im sure an extra fan would be a good idea. but i could never really figure out a good relay/system for getting it to go on and off.

[DaveAZ]

It did cycle on and off some at stoplights during the summer, but never that long really. I do run an fmic, so im sure an extra fan would be a good idea. but i could never really figure out a good relay/system for getting it to go on and off.

We got one of those fancy gold anodized blocks that replaces the stock head water inlet housing on the top of the motor behind the cam angle switch. To that, I threaded a 1/4 NPT temp switch, set at 185. That powers a standard relay. The relay controls the engine cooling fans. I am going to use that temp switch to power an additional relay for the condensor fan.

You could do the same thing, only just for your condensor fan. Or, Summit sells those radiator hose temp switches. Never tried those though.

[jontron5000]

I'm looking to get AC into my SR20 also. My car is also originally an s0hc :(

From what I've read you said that you used the AC components from the DOHC KA right?

I know that the compressor and lines are different on the DOHC, but how about the condensor and evaporator? Do the original SOHC ones fit with the new DOHC lines and compressor?

[DaveAZ]

From what I've read you said that you used the AC components from the DOHC KA right?

Sorry it took me so long to come back to this. The "only" DOHC component used was the compressor. Courtesy Nissan says they can't source a few of the lines I wanted, and what they did send were the wrong lines. (Or I ordered the wrong lines)

I modified the SOHC lines to fit "better" on the DOHC compressor. This involved cutting off the extra mounting bolt flange from the SOHC lines. The rest of the system remained SOHC.

I know that the compressor and lines are different on the DOHC, but how about the condensor and evaporator? Do the original SOHC ones fit with the new DOHC lines and compressor?

I am almost positive both DOHC and SOHC condensor fittings are the same. I was able to get the OEM SOHC receiver/dryer, so of course it bolted right in, and all lines fit. You need to replace this item. Obviously, the SOHC lines bolted right to the evaporator (firewall) connectors, since that was original.

I spliced on the SOHC electrical connector to the DOHC compressor, and of course the ECU wiring needs to be done right. The biggest challenge was getting the Frikking O rings to work with the modified lines. I used a large misc. kit of green o-rings to end up with the right ones. Used silicon grease to hold them in place, then compressor oil to install them. Also had to deal with numerous stripped aluminum fittings on condensor. Aluminum galling.

Sorry so long. It took me months to piece this together, and I am still amazed it's working. lol..

[jontron5000]

Thanks for the info. Can you tell me more about the wiring portion?

I rewired my harness based on the wiring write ups for the SR20. Does anything else need to be wired or am I good with this?

[DaveAZ]

Thanks for the info. Can you tell me more about the wiring portion?

I rewired my harness based on the wiring write ups for the SR20. Does anything else need to be wired or am I good with this?

The info in FRS about which of the two wires to use was valid, as was "most" of the available info on wiring that I found. I ended up marrying the stock schematic with the 180SX schematic.

Definitely a lack of information on S13 SOHC applications is what I discovered, and definitely little spoken about SOHC lines and DOHC system interface.

It gets tricky when swapping individual components with wiring, like compressor, condensor fan, and evaporator "if" someone has hacked out the wiring for those items.

[jontron5000]

Do you have a picture of the electrical chasis plug that goes into the DOHC compressor?

Some genius (previous owner) decided to cut off the plug for some reason..

[DaveAZ]

Do you have a picture of the electrical chasis plug that goes into the DOHC compressor?

Some genius (previous owner) decided to cut off the plug for some reason..

No, sure don't. If you can't locate the wire, it's on the front left side, right near the AC relay, single wire, all by itself.

From your post above, you have a SOHC car right? On the DOHC compressor, the power goes through a pressure switch on the compressor itself. Since that system is missing from the SOHC's, I removed the wiring from the compressor, and soldered the plug right into the car harness.

[jontron5000]

No, sure don't. If you can't locate the wire, it's on the front left side, right near the AC relay, single wire, all by itself.

From your post above, you have a SOHC car right? On the DOHC compressor, the power goes through a pressure switch on the compressor itself. Since that system is missing from the SOHC's, I removed the wiring from the compressor, and soldered the plug right into the car harness.

What wire did you use on the car harness to solder for the compressor?

[DaveAZ]

What wire did you use on the car harness to solder for the compressor?

It's a single brown and white wire coming from the AC relay. Sounds like you have to dig for it, maybe splice it longer and put a connector on.

[jontron5000]

Okay thanks for the help thus far. What kind of connector did you end up using for it?

[DaveAZ]

Okay thanks for the help thus far. What kind of connector did you end up using for it?

DORMAN Part # 84707 and 84708 available at Rock Auto would work for you. You'd have to (most likely) splice both ends on. (One to the compressor) as they are listed for the SOHC compressor. They look just like the fitting I spliced on. Sure, the next poor bastard who has to change the compressor will have a fitment issue, and be right where you are at now. :) It'll be the least of his worries.

Bottom line is that it's simple one-wire connection and if it was the only thing stopping me from using the AC, I'd just splice the wire.

[codyace]

Dave, I hope you don't mind but I may take some of this information for a FAQ page on my website...is that ok? I really appeciate you being the first EVER going this in depth in regard to the SOHC to DOHC...I've had guys tell me it works, but that's the end of it usually. Rockin stuff!

[DaveAZ]

Dave, I hope you don't mind but I may take some of this information for a FAQ page on my website...is that ok? I really appeciate you being the first EVER going this in depth in regard to the SOHC to DOHC...I've had guys tell me it works, but that's the end of it usually. Rockin stuff!

LOL, no problem on my end Cody. While I was trying to piece this together, I did all the usual searches and found very little on the SOHC. Nissan made so many changes to the system, and so many of the lines are no longer available, DOHC or SOHC.

The plug part numbers I posted above are for SOHC systems. I couldn't find the DOHC plugs on line. I simply spliced in the SOHC compressor plug into the DOHC compressor. That allowed the use of the stock SOHC wiring harness (plug). Better to have used the DOHC plug and spliced it into the car harness, but didn't have it.

[jontron5000]

DORMAN Part # 84707 and 84708 available at Rock Auto would work for you. You'd have to (most likely) splice both ends on. (One to the compressor) as they are listed for the SOHC compressor. They look just like the fitting I spliced on. Sure, the next poor bastard who has to change the compressor will have a fitment issue, and be right where you are at now. :) It'll be the least of his worries.

Bottom line is that it's simple one-wire connection and if it was the only thing stopping me from using the AC, I'd just splice the wire.

I found a guy who will sell me the AC compressor connector from a DOHC from his chasis. Can I use this plug and just splice the brown/white wire you were speaking of earlier?

Thanks:goyou:

[DaveAZ]

I found a guy who will sell me the AC compressor connector from a DOHC from his chasis. Can I use this plug and just splice the brown/white wire you were speaking of earlier?

Thanks:goyou:

Yes, and that is the preferable route to go.

[jontron5000]

Perfect, thanks a bunch for your help!

Hopefully it will work on the first try lol

*fingers crossed*

[jontron5000]

There is a lone wire on the driver side near the fender wall where the old SOHC connector used to plug into the SOHC compressor. Should I use this wire for the new DOHC compressor as well?

[DaveAZ]

There is a lone wire on the driver side near the fender wall where the old SOHC connector used to plug into the SOHC compressor. Should I use this wire for the new DOHC compressor as well?

Yes. However the SOHC connector probably won't mate with the DOHC connector. You will have to modify it with a single spade-type female to fit it.

[jontron5000]

Yes. However the SOHC connector probably won't mate with the DOHC connector. You will have to modify it with a single spade-type female to fit it.

the plug on this wire was already cut off previously so I guess it all works out. Thanks! :wiggle:

[Eggdrop]

So I've searched on this topic for a bit and had some basic questions. I have a 89 se with a redtop. Car never had ac so I am missing everything. What am I looking for exactly to have a/c? I was quoted about $650 to get everything done. Is that a decent deal?

Sent from my Lumia 900 using Board Express

[DaveAZ]

So I've searched on this topic for a bit and had some basic questions. I have a 89 se with a redtop. Car never had ac so I am missing everything. What am I looking for exactly to have a/c? I was quoted about $650 to get everything done. Is that a decent deal?

Sent from my Lumia 900 using Board Express

If that $650 includes labor, hell yeah it's a good deal. You need the entire interior portions, including the control box, the actual cooling unit, door control, any wiring and ducting- some of which may be there. The HA section of the FSM lists the components.

Then you need the entire hose/pipe assys in the engine bay, AC relay, condensor, fan, receiver/dryer, compressor, and a special mount for the USDM compressor to mount to the SR block.

Then you have to modify the SR wiring and adapt to the 240SX wiring, (ECU) and man, that is a big job. I doubt the local AC shop down the road would be able to complete this job unless they specialize in SR/240 cars.

Yeah, 650 would be a good deal in my opinion if you are starting from zero.

[Eggdrop]

You mentioned ecu, will I have any issues because I'm running a PowerFC?

Sent from my Lumia 900 using Board Express

[DaveAZ]

You mentioned ecu, will I have any issues because I'm running a PowerFC?

Sent from my Lumia 900 using Board Express

No idea. The SR ECU provides a ground signal to just about everything in the engine compartment that has to do with AC. (Pin 106 iirc)

If I were contemplating a job as big as the one you are looking at, I would consider running a toggle switch to provide that ground for the AC relay instead of using the OEM setup. Then I'd consider an aftermarket underdash unit from one of the "classic car" parts suppliers.

The first thing you need to do is check out the 240SX FSM, and the well-published SR ECU pinouts. Using the SR computer allows the high idle to kick in as well.

Respectfully, if I lived in NY, I wouldn't even consider this, unless the original chassis came with the system, or I had total and complete access to a car with all of the AC parts in it. "Then" you'd only have about a week of swapping and wiring to do.

Recommend you run this by Cody Ace on here, as he has some very good knowledge of these systems and sells compressor adapters.

[Eggdrop]

I need to update my profile, lol. I live in Miami now and the a/c thing is necessity. I will see what I van find out. I will also speak to the guy who says he can get me all setup. Thanks for the help!

Sent from my Lumia 900 using Board Express

[SSonic92]

Hey, i sent a email to codyace and posted a thread on nico about trying to do a setup similar to your setup, could you post pics of how much you cut off the lines so they would bolt onto the compressor? You are the only one so far i have found that has any good info on sohc to dohc. I also have a wiring specialties harness so my evaporator/ dryer dp switch plugs in to the harness, so the only thing i need to do is get those two plugs you put part numbers for from dorman and everything should hook up and run right? i know i have my plug for my fan on the condenser that wont plug up but i have dual electric fans and a thermostatic switch that cuts those on, and it has a wire for the ac so that it will cut on when i turn on the AC. Which wire would i tap that into? Heres a link to my thread and if you could email me too i thank you a bunch, getting hot as hell and would really like ac.
Sorry to thread jack.
Email: [email protected]
Thread: A/C questions, Help please (codyace) and anyone else who can : SR20DET Forum (rear-drive) (http://forums.nicoclub.com/a-c-questions-help-please-codyace-and-anyone-else-who-can-t559756.html)

[ultimateirving]

other then that little can, it doesn't matter where you cut them. Just make sure they fit the compressoryou are using. and the other end matches up with the firewall
http://i3.photobucket.com/albums/y70/guitarist_of_punk/IMG331.jpg

[SSonic92]

other then that little can, it doesn't matter where you cut them. Just make sure they fit the compressoryou are using. and the other end matches up with the firewall
http://i3.photobucket.com/albums/y70/guitarist_of_punk/IMG331.jpg

thats not what i mean by cutting it, he said that he cut the actual end so that it had just one bolt hole, bc the sohc lines have to bolt holes, thats what im trying to figure out, is all that around the hole just aluminum to bolt down or does it open up inbetween those two bolt holes? or is that cut already? the hose i have to get from the firewall to the compressor wont have that little can on it.

[SSonic92]

And for the plug that is on the compressor, i can just cut that connector off, and the one on the plug for the sohc line and just get blade connectors right? Reason im talking like this is bc i dont have the line yet coming off the firewall and the compressor yet. picturing everything in my head.

[SSonic92]

A/C Line-Compressor to Evaporator (Front Pt)-1995 240sx | eBay (http://www.ebay.com/itm/A-C-Line-Compressor-to-Evaporator-Front-Pt-1995-240sx-/290730368755?pt=Motors_C)
ar_Truck_Parts_Accessories&fits=Model%3A240SX&hash=item43b0e15ef3&vxp=mtr#ht_500wt_969

ok so this line should work right? from the pic you have up of yours? it says its for a 95.

[oskie]

Hi guys, I have a question regarding my AC system. I have a sr20det redtop and I bought my car with the AC lines not yet connected. I managed to have a local AC shop connect the lines and make the AC system work. It works fine now. They wired it without any connection to my ecu.

So now here's what's bugging me, running the car while AC is on when I hit the brakes my rpm drops to 500-600 for 1-2 seconds almost close to stalling but never does. In neutral, my rpm is at 850-900(warm engine) and when I turn the AC on it drops to 600 for 1-2 seconds the goes back to 850-900. With the AC off my car runs fine without the rpm drop when I hit the brakes.

What seems to be the problem? Is it the IACV? I've read that there's supposed to be a wire connection from my AC system to the IACV for idle up is that right? Coz mine doesn't have any. Or is there anything else I should check? Thanks in advance!

[drifter92]

Omfg, I just found this thread and I'm blown away.... I will be ordering some as soon as my SR comes in......