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.

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Z32 with lq4 swap
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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'.

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DaveAZ

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.

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!

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Z32 with lq4 swap
Desert Street Scene || Dssevents.com

DaveAZ

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.

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Z32 with lq4 swap
Desert Street Scene || Dssevents.com

DaveAZ

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.

__________________
Z32 with lq4 swap
Desert Street Scene || Dssevents.com

DaveAZ

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?

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DaveAZ

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 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?

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DaveAZ

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..

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DaveAZ

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

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

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DaveAZ

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?

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DaveAZ

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!

__________________

Want Air Conditioning in your SR20 Swapped car? Check out www.sr20acbrackets.com for more information!

Quest Alternator Conversions for SR20! Check my Group Buy!

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DaveAZ

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

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

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DaveAZ

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*

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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?

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DaveAZ

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

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

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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?

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