Most perplexing; there are two diagrams (see attached) in the service manual for 1991 5.7 L Camaro about secondary fan pressure switch that is diametrically opposite in their functionality, as in OPEN or CLOSED default circuitry:
1) one at page 988 (6E3-A-6) under Driveability and Emissions section where it denotes the switch to be N.C. (Normally Closed, which means 2nd fan is always on), opening (meaning closing the fan) at 190 psi.
2) another at page 1154 (6E3-C12-2) under Driveability and Emissions section where it denotes the switch to be N.O. (Normally Open which means 2nd fan is always off WHEN the A/C is off, UNLESS operating temp is above 238 F when the fan is activated by temperature switch, so irrelevant), closing the switch (meaning opening the fan) at 233 psi.

My pressure switch was shut and I bought WVE 1S16236 (14078970 OEM) listed as "Refrigerant Pressure Switch" BEFORE figuring out what's what as explained above and now the 2nd fan is always on with ignition on as it would per Option 1 above; HOWEVER, Four Seasons 36669 (14078970) brand switch lists as "Fan Closed" pointing out to the fact that Option 2 above will be the case where the 2nd fan will be ON when the A/C is ON.

All that leads to this simple deduction: there are in fact TWO differently operating switches for my car; but what gives? My best guess is that the options are climate-dependent and if one drives in rather hot climates should chose Option 1 switch where the second fan is always ON, and the Option 2 switch when driving in moderate to cold climates where the second fan acts primarily to cool the A/C compressor.

If anyone has a definite answer, please let me know.

 

Also, the connector had same color cables; is it possible that the ECM and ground cables are switched around when I connected them to the (one-way) socket and causing the switch to be on since the ECM pin would be grounded at all times in that mix-up?

 

I don't know how your wired,... I don't know the answer to your question,... but this these diagrams were taken from the 91 Camaro shop manual and they are the diagrams that specifically covers the TPI dual fan set-up. Both diagrams show the stock AC pressure switch as a N/O switch that closes at 232 psi; These are the diagrams I would follow.

 

I have all that, the whole manula 2041 pages long As I explained, my wiring is OEM. The issue w/ the switch which has been discontinued by AC Delco since 2012, is that there are ONLY NC type (Normally Closed circuitry that keeps the 2ndary fan on at all times) as it is shown in one of diagrams I posted. In fact and as I explained, those two diagrams I posted are contradictory: one says NC and the other NO (Normally Open circuitry) which are polar opposites in terms of operational function. The solution I concocted is this: From May to October, when I have A7C on all the time, I will keep the socket plugged that will engage the 2ndary fan on whenever I drive and also will put a manual switch under the dash going to the 2ndary fan relay that I will flip on during cold months if temp rises too much to cool the compressor. No other solution exists other than finding a switch that would fit the threads AND would work on NC (Normally Closed) operation.

 

On the f-body cars it is supposed to be a NO switch (A/C pressure status to ECM).

The y-body cars used the NC switch, probably how it ended up wrong in the one wiring diagram.

RBob.

 

Thank you; I appreciate this clarification that finally makes sense One caveat on the engineering design of F-body, though: My block is 4% enlarged during the rebuild, bringing the engine size to approximately 6 L, which literally translates to slightly more hot running engine and w/ refrigerant/2nd fan pressure switch (NC) plugged in, the temp never goes above 160 F / 70 C at about 70 F / 20 C ambient temperature since the 2nd fan is always on; that obviously is causing a serious decrease in the efficiency of internal combustion engine. All that makes me circle back to my original thought: Since the two-switch (one temp and the other pressure triggered) for 2nd fan design is no longer supported (as I assumed) and AC Delco discontinued the part since 2012, it is nowadays used for always-hot-climate-driven F-bodys and bypassed by one of my earlier proposed designs in all-season climates during cold/cool weather.
Further, Four Seasons brand carries a description of N.O. mode that does not correspond w/ its actual operation, hence my troubles; this brand is one of only two available; the other being WVE that did not carry any info about N.(C/O) mode and what I purchased first, then returned as "defective" only to replace it w/ Four Seasons to no avail since the latter's actual (N.C.) operation contradicts its claim.

 

Question: I found one Delco (Remy?) original that is listed for Corvettes C4,5,6 and verified compatibility; it carries the same AC Delco (14078970) and OEM part numbers; seller informed me that the original package contains no information about its normal operational mode but obviously it is manufactured when N.O. was available: do you think it is N.O.?

 

Just measure the resistance between the two terminals, should be infinite.

RBob.

 

Superb idea: Reads NOT infinite. So, WVE produces N.C. switch, apparently for hot climates, or people who'd like to operate their A/C ON year round at all times Regardless, I must assume the Four Seasons brand on it now that shows exactly the same operation mode must also be N.C. although their info page at Rock Auto claims "Fan Closed" which must indicate N.O. switch but I think they made a mistake and meant SWITCH Closed; regardless, I dropped them an email asking what's what. Although RA refused to reimburse me, after contacting WVE, they agreed to give my money back

I pulled the plug for the winter and will install a manual switch under the dash that would kick in both fans when necessary, bypassing 2nd fan pressure switch for both to be on at all times when I throw the **** on, and will connect it back between April and October. The only pickle is that the 1st fan will not kick in when I turn on the defrost but I am not much worried when ambient temp is 60 F or less as long as I have the manual switch to kick them both in. Besides, the temp switch for the 2nd fan is working just fine.

Since the FS brand is on the car, it's harder to measure it but I will do that and post the result here soon although I doubt the result will be any different.

 

This is an interesting thread. What thermostat are you running? I used to have a 160 stat with Hypertech chip that turned the driver side fan on at 176°/off at 165°. The fan was on about 99% of the time in 70° weather. Temps would never go past 175° on the dash gauge. That was during my Canada years. Switched to a 180° thermostat and put the stock chip back in. Ran warmer obviously. Went to a 200/185° fan switch. Moved to Texas. This setup keeps things around 180-185° during mild weather. 190-200 during hot weather. And 210° during HOT Texas summer weather. Having said all that, it's all moot when the air conditioning is on during the summer because that will kick the fans on due to pressure and the temps are high anyways regardless of fan switch or computer chip turn on points.

On a cooler Texas day in November, I've seen the passenger side fan turn on and off while idling in the driveway with the A/C on (watching pressure on A/C gauges rise to 230 psi, fan turns on, lowers to 190 psi, fan turns off. Driver side fan stays on because the cycling of the A/C isn't off for long enough for it to turn off at any point even though the coolant temperature is low. This is on a cold engine in say 65° weather.

In your case, maybe I'm reading it wrong. But the normally closed or normally open shouldn't make a difference. Because if it's normally closed (fan running), it should trip the low pressure switch and turn the fan off. And if it's normally open, well then it should be off anyways. So I'm not seeing why the fan would stay running all the time in cool weather that has no/low A/C usage........Now if we're talking about the driver side fan being on all the time due to it being N.C., I would raise the thermostat to a higher temperature. With that, the engine should stay in the range you desire. It would just be the driver side fan running unnecessarily.

The page 1154 #2 option you describe in your thread is how I always understood the fans to run in regards to temperature and pressure. In other words, the secondary fan is off unless it's 238°F or 233 psi, whatever happens first. Should be this way for all the 1988-92 cars. The 1987 year was the only year that did not have a high psi turn on point for the secondary. It ran at 238°F only (and probably had bad A/C performance in all but the hottest climates)

 

If your thermostat is working correctly your fans can be on all the time, thermostats regulate minimum temperature so if you have 180 degrees thermostat the coolant will stay in your block until 180 degrees, then the thermostat will open and let it go over to the radiator and when it falls below 180 degrees it shuts and starts the process again. So your fan cooling engine coolant in a closed radiator isn't doing anything but wasting electrical energy by running when it shouldn't.

 

Good arguments. We are not talking about the driver side fan as I assume its operation is normal:
1) it comes ON when I turn on the A/C, as it should from what I read in the schematics (also triggered through ECM's BD12 Fan Request Signal via 2nd fan relay's F terminal onto 1st fan relay's F terminal), naturally, this being true when the 2ndary fan switch is plugged in.
2) also around 220 F when:
i) 2ndary fan switch is plugged OFF during cold weather, when 2nd fan being OFF under normal conditions,
ii) 2ndary fan switch is plugged ON during hot weather, when 2nd fan ON at all times.

Also, tested the 2nd fan being triggered through temp switch (238 F) and that also works correctly.

Thermostat is OEM style 195.

As I posted a quick reply just before your post: the high pressure switch is indeed N.C.; measured between its terminals and the result is not infinite. In terms of your explanation about the low pressure switch that would be triggered w/ that setup, closing the 2nd fan OFF, I don't see it happening based on the schematics since the low pressure switch is not on that circuitry.

What's really annoying is the fact that I assumed all that above is caused by a faulty or N.C. manufactured WVE switch (WVE accepted to issue a full refund upon my similar explanation, but w/o clarifying its normal operation mode) and bought another from Four Seasons brand that is causing the same predicament although they advertise it as <Operation: Fan Closed> that should mean the switch is N.O.. I need to measure that one, too, but couldn't get around it yet, although I'd be surprised if it'd turn out to be N.O. since there would be no possible explanation left for this predicament, at least none I can come up with.

 

All that true, although not exactly, since the 2nd fan being kicked in w/ 185 psi on the A/C high pressure line has nothing to do w/ engine temp. In this current incorrect operation, I believe the 2nd fan being ON at all times causes the engine block to be cooled also via convection in cold weather, causing the coolant temp never to be raised above 195 and temp gauge reading pretty much never above 160-ish (half way mark between 100 and 220). Proof is the fact that,when the switch is unplugged and 2nd fan is not triggered at all times, the thermostat opens up at 195 F, temp gauge comes up to 220 and 1st fan kicks in, keeping the temp steady at/around 220 F during all operation, as you explained in normal operation. But I agree that this set up (2nd fan being on at all times) is not efficient at all in terms of energy. All in all, very puzzling and as I explained earlier, I am trying to simulate the N.O. switch / 2nd Fan Closed operation by installing a manual triggering switch for the 2nd fan to be used w/ A/C on (rarely needed for extended periods during winter here) and keeping the 2ndary fan pressure switch unplugged during cold weather.

 

Why not just piggyback off the compressor circuit?
when the compressor is turned on you could have a leg that also turns on the relay for that fan. Just put a diode in the leg you create to keep it from back feeding and it would allow it to still function from pcm control. Just put a diode on the pcm control wire so your new leg doesn't backfeed into the pcm.

 

If you used two diodes to do that you could go a little further and use LED's so you could even tell if and which circuit is being used at the time

 

Good idea, but it is easier to pull a wire from 2nd fan relay; already have one for 1st in case of emergency so I'll connect that one onto the same switch I placed under the dash.

 

I was looking at the wiring diagram for your car while I'm at work. its a pretty simple circuit lots of options for modifications. Its odd to see 3 ground control options in parallel. I work on more modern cars so looking at things like this makes me wonder their thought processes that made the engineers do that. Vs just sending both of those signals to the pcm and let it do all of the fan control. It would be cool to be able to go back and see all of the engineering changes in that Era.

 

 

Important information: WVE product department just confirmed my suspicion: WVE part 1S16236 < (refrigerant/secondary fan) high pressure switch > is N/A for 1991 5.7 Camaro w/ A/C; waiting a similar confirmation from the only other brand carrying this part (now THE only one: Four Seasons part 36669) and will also post it here when it comes.

 

That legacy switch I found w/ exact OEM part number (AC Delco 14078970) also measures 1 to 1/2 ohm at 10 ohm dial setting, too, just like WVE who told me this is not the part for my car in the first place. All this mess is not only confusing but makes me believe that these switches were made at N.C. mode, kinda weird, don't you think? I am fairly sure I am not making a measurement mistake. Flabergasted, indeed!

 

Following, because I just went through this and the only source for the switch that fit was on eBay for like $140.

 

I don't trust those "fits" anymore since the part manufactured by Delco (14078970) w/ OEM part number 15-2351 also is N.C. per my measurement as I explained above. The fact is, I am suspecting the design of 1991 Z28 5.7 L w/ A/C is in fact N.C. for that switch since there are two conflicting schematics.


Yet, Four Seasons part (the one on the car) claims Fan Off under normal conditions and they have not responded to me. Of course, there is always a possibility within statistical reality the FS part is faulty and that Delco part may do the job since I highly doubt that one to be the wrong one w/ both OEM and Delco part numbers on the box: My ohmage measurement may be resulting between 1/2 to 1 ohm for another reason than the circuit being normally closed; after all, I am not an A/C specialized electrician

 

You could also test it by putting a ground lead to one pin and have your test light to battery positive and touch the other pin with the testlight. If it's a normally closed switch the light will illuminate.

 

True but correct me if I am wrong: when it is plugged in and I only turn the ignition on but not start the engine, I literally apply the same procedure but w/o the test light but the fan which comes on that is akin to test light illuminating, ergo: N.C. circuit. My problem is w/ Four Seasons data sheet claiming otherwise (and they still not responded unlike WVE) AND that legacy Delco OEM part doing the same upon measuring it (see attached video; setting 10 Ohms)

 

Btw, after careful review of both schematics, I concluded that the only difference is the starting position of the fan when ignition is on, since according to N.C. mode, it opens at 190 psi which means that setup starts with 2ndary fan ON but immediately sees high pressure line to be less than 190 psi and turns OFF the 2ndary fan by opening the circuit; on the N.O. mode, it starts w/ fan closed and only closes the circuit when high line reaches 233 psi, turning the 2ndary fan ON. It literally is the same difference in terms of continuous operation. All this makes me conclude that I have a faulty switch on my car. Could you concur?

 

It is really straight forward, the '90 - '92 TPI f-body uses a NO A/C pressure switch. With high pressure the switch closes and that does two things:

1st, it turns on the secondary fan via the relay.

2nd, it tells the ECM that the secondary fan has been enabled. So that it will enable the primary fan.

Note the secondary fan coolant temperature switch that is in parallel with the A/C pressure switch. It too is a NO switch. So either one will do the above (sec fan on and ECM knows). This is why folks run a switch in the interior that grounds that wire, to TURN ON THE FAN(S).

Again, the A/C fan enable, ECM notification, switch is NORMALLY OPEN (NO) in operation. And closes with high A/C pressure. Same as the head coolant temperature switch.

RBob.

 

So if the switch is normally closed and the correct one is normally open but not able to be purchased. Does the switch you have open at high pressure? Or is it just closed all the time no matter the pressure because it's broken?

 

Thank you,in fact you mentioned the other thing that is puzzling me and that may give you a clue as to what's wrong beyond the pressure switch: I read all this is also in the service manual to make sure I am not missing anything, and I already tested the coolant switch a long time ago which works fine, bringing the 2nd fan on around 235 F while the 1st is already on since the coolant temp is already beyond 220 F.

Weird thing about this pressure switch operation is, although the 2nd fan is always on due to FS brand switch w/ ignition on, when I turn on the A/C, 1st also comes ON as it should, as you and the service manual describe; that operation must be pointing out to the fact that the pressure switch is sensing the high line pressure exceeding 233-250 psi and therefore working as it should, does it not? IF this is TRUE, if I must assume the switch is indeed working properly, then the only explanation for the 2nd fan to be on at all times, given your explanation, is that fact that this grey wire going through both switches in parallel and to the ECM and 2nd fan relay is somewhat grounded at all times, correct? YET, I measured the grey cable at the junction AND at the connector, resulting to show that grey cable is NOT grounded, which is, technically speaking, good and proper circuitry. Conclusively, I have been chasing my tail, looking for a faulty switch that is (2nd fan is ON all the time) and isn't (1st fan is kicking in when I turn on the A/C, indicating the pressure switch is working). This literally looks like a quantum state that cannot be! Am I missing something about the pressure switch's operation? As in, irrespective of the switch being NO or NC, when I turn the A/C, 1st fan also should come on as it does because of the ECM that registers A/C being on and signals the 1st fan to kick in. If this is true, then, I am back to square one, having installed a NC switch despite its data sheet claiming otherwise.

Another thing is, having either switch should not make a difference in practice since NC would have the 2nd fan on at ignition but seeing the high pressure line at less than 195 psi (A/C OFF) would open up, causing 2nd fan to stop, whereas a NO switch would have the 2nd fan OFF only to kick in when high pressure line exceeds 233 psi. Same difference, indeed.

 

Part numbers are somewhere above but, yes, always closed w/ 2ndary fan on at all times w/ ignition on; parts purchasing history is as follows:

First one was WVE, Rock Auto refused a refund, I contacted the manufacturer who admitted they mislabeled and mismarketed the part--which is not for ours--after talking to their engineering dept.; then they engaged Rock Auto to issue me full refund.

Second one was Four Seasons, Rock Auto refused a refund, again, I contacted the manufacturer w/ all the videos, bells and whistles to prove that there is a positive reading between terminals on the unmounted switch; they submitted it all to their engineering department and I am awaiting an answer.

Third one was from ebay and it was inside a vintage Delco labeled box that has proper and correct Delco and OEM part numbers imprinted, but it also turned out a closed circuit, resulting a positive reading (1 to 1/ 2 ohms at 10 Ohms setting) so I returned it for a refund.

Conclusion: Unless Four Seasons come back to me claiming the one I have is faulty and in fact they manufacture a NO switch as their data sheet claims ( I asked for a/v or at least picture proof of that if they were to claim so), there is no unused, brand new high pressure refrigerant pressure switch manufactured w/ Normally Open circuit in the whole wide world anymore, at least for my car.

I also explained my solution somewhere above, if that predicament were to become permanent: I already have installed a manual switch under the dash for the first fan, I will connect the 2ndary fan relay ground terminal to that one, too. I unplug the connector during cold months and only throw it up jic, and have it plugged in during hot months since A/C is constantly on and 2nd fan must be engaged to keep the temp even at 220 even w/ the 1st fan coming in and out around 220ish F. Alternatively, I may go around to find one that would fit w/ similar characteristics and adapt it to my car as long as the threads fit.

Bummer, indeed, since all is stock in my car except this one, now.

 

Be easy enough to use a relay or a transistor to invert the switch function...

RBob.

 

that's exactly what I was thinking

 

if my 88 has the same switch, i can just send you the one from my car. I'm not going to use it once I start with my LS swap.

 

You are talking about changing the polarity; great idea as long as you explain to me--if you don't mind--exactly what type of Relay or Transistor I should use and how I do it; I am not well versed in "electrons"

 

Wow! That'd be so cool! Let me know when you go ahead w/ the swap please

 

Their are a few ways you can do it, this is a way using a 5 pin relay, 87a is connected when the 85/86 circuit is open, so doing it this way when you turn on the key it will trigger the 5 pin relay on and open the ground connection that is making your fan relay activate. So basically turn off the ground until your pressure switch that is normally closed opens. Once that is open the added relay will switch over to 87a and your fan relay will be grounded and turn on your fan.

 

I am sure it is my inexperience, but let me try to put it in a form that I'd understand:
Assuming I did the connections as you diagrammed, when ignition on, 5-pin relay is triggered and opens the ground, causing the fan NOT to activate.
Q1: In this case, is the pressure switch supposed to OPEN when A/C is turned on, contrary to OEM ops? Because it doesn't now; if it were, the 2nd fan would stop working since no longer grounded. I understand that as once the switch is open, the fan relay will be grounded through 5-pin's 87a and fan will be ON, but what will cause the switch to open? This where I am totally lost
Q2: Also, will this setup interfere w/ temp switch's ops since it is on the parallel line w/ pressure switch?

 

You would put it in after the splice at roughly this area. It would allow the other parts to function as they are supposed to, but this will only work if the switch that you currently have that is normally closed will open at 232 psi , If it is normally closed and never opens even at high pressure then this wont work.

 

You would need to separate that ground that is coming from the pcm and make it have its own dedicated ground.
or separate the switch to its own. Whichever is easier for you. But those two can't share a ground

 

Now got it: I am doubtful the switch will open up at 233 psi: this wouldn't make sense. Besides, it may be faulty; still awaiting a definitive answer from the manufacturer as the contact person fwd'ed my explanation and videos to their eng'g. dept. I will proceed once they answer. Btw, IF the switch is NOT faulty but mislabeled as NC, it should have stopped after 60 seconds of ignition seeing the line pressure being less than 185 psi which doesn't, that makes me believe the switch IS indeed faulty; I deduced NC and NO modalities both work practically the same way starting from different ends, based on the schematics I put up at my original post that shows operating conditions of both.

 

It depends on which side of the oriface tube it is. If it's after then it will be a high pressure switch. So once the compressor is on it will be roughly 200 psi. If it's before then the pressure will usually always be below 90 psi. 90 is normal static pressure with the whole system off. Once the compressor is on low pressure will usually be close to 40 +/- 10psi. So judging by the schematic saying the switch close at 232psi I would guess that switch is on the high pressure line.

 

Also I looked on my 88 and I didn't see that switch in the right side of the engine bay where the schematic said it would be.

 

Yes, of course: it is a high pressure switch. As I explained above, NO and NC both works to the same end from different directions, but since 2ndary fan never stops, it can only mean the switch is NOT operating AT ALL and stuck at CLOSED position. For the time being, the intermediate remedy I did was to install a manual grounding switch by splitting the ECM cable (grey) terminal on the 2nd fan relay and attaching a cable leading to it at the interior, under the dash, and unplugging the connector; this may as well be the permanent solution, bypassing the switch during cold weather and plugging it only during hot weather since A/C is constantly on. But all depends on Four Seasons' response about their product, too.

 

Do this and when you turn on your ac it will turn on your fan, but still let it operate in all other ways. It will omit the pressure switch completely. The fan wont come on just because the key is on.
also if you're low on freon and the compressor won't come on, neither will the fan. It's more than likely your best permanent solution because the only thing that will change is the pressure required to turn on the fan.

 

Sounds good; as soon as I hear from Four Seasons, I'll look into it.

 

Rock auto responded w/ this line: "I have checked the order history for Fours Seasons Part # 36669. We have sold this part well over 100 times in the last 9 years. We have only had 1 warranty return for this part in that time."

I am having a hard time understanding this other than the very statistical possibility that I have received a defective switch, and may be biased because of the fact that WVE has mislabeled its switch (see the discussions above, somewhere) BUT, I'd think at least one or two people on thirdgen would have bought this part and shed some light to the predicament Regardless and just to make sure, I bought another one and tested it leading to the same result so Four Seasons 36669 is indeed mislabeled.

Further, Four Seasons representative finally responded that I should instead buy part 36666 that has very similar specs (175 to 220 psi), implicitly accepting mislabeling 36669 (I noticed that, in fact, this part is manufactured as N.C. per the sticker label put on it when made in China that clearly denotes its specs). I have fwd'ed all email thread w/ Four Seasons, including videos of tests w/ a multimeter to Rock Auto, AGAIN, this time asking for a store credit that I'd apply to buy that other part; although my pleas have fallen on deaf ears and this predicament has pissed the hell out of me as a 20+ year Rock Auto customer until now, they finally agreed to give me a store credit valid for five years upon returning the mislabeled part.

 

I purchased and tested FS 36666 that results in N.O. circuit as it must, also proving that the sticker on the 36669 switch itself indicating N.C. operation is correct despite its information sheet: do NOT purchase 36669 from ANY dealer as all of them are carrying it mislabeled; instead go w/ 36666 that has similar operating parameters.

 

Nice. So I'm guessing your journey is nearing an end?

 

Good find, this will be helpful to many folks.

To really throw a cog in the wheel. The '90 - '92 MPFI Camaro/Firebird cars (V6) used the N/C switch. This just dawned on me as I read your/this post. When folks removed the A/C systems the cooling fan would always run. Needed to ground the switch wire that goes to the ECM to prevent this.

Dang, something different every time...

RBob.

 

The Diagram on the Relay also indicated that there is a Suppressive Resistor also placed across the Relay Coil for any Voltage Transients that occur as the Magnetic Field collapses.
A Reverse Biased Clamping Diode is often used instead.

Years ago it was more common to add a suppressor to a cheap relay that did not come with one.

 

I've wondered about that. It's on most any relay I've ever worked with. I was thinking it was kind of a buffer to keep the relay from fluttering in the instant that it was activated or deactivated.