1988 corvette, don't understand what it's doing?

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tourmax
Posts: 40
Joined: Wed May 13, 2020 2:26 pm

Re: 1988 corvette, don't understand what it's doing?

Postby tourmax » Sat Jun 06, 2020 5:32 pm

So I've been digging around while waiting for parts. A couple issues have arisen.

1. Charge. My FSM ( real, not haynes or clymer) lists the charge for R12 (original fill for my 88) as 2.75 lbs. Labels on the car agree with the FSM. BUT.....while digging around in the TSB's for an 88 corvette, I came across a very short and brief service bulletin that CORRECTS the FSM. Seems GM spec'd the 88/89 Vettes at 2.25 Lbs, not 2.75 lbs as listed in the FSM and on the car labels. Somewhere along the way they had a printing error I guess, or someone at GM just plain effed up and incorrectly spec'd 2.75 lbs. So I would have been overcharged by at least .5 lbs if using R12, the equivalent of half a can of redtek (by their equivalency charts). Not sure if that was my whole problem, but it sure as heck wasn't helping it. No matter how you slice it, I was overcharged, by a fair amount. Seems to fall in line with most of the symptoms/problems I was having.

2. Cycling switch. Well, seems an r12 switch was set for around 25 psi and the R143A switches (later years) were set at around 20-22psi. Looking at the Redtek charts, it looks like it wants to be somewhere down around 20 psi. I've read several comments around the web that because of redteks temp glide, it's hard to say where the switch should be set and it's more of a "try it and see" deal to get a good setting.

As to which switch is already in my Vette, who knows? it could be either. I have no idea if anyone has ever changed it. Seems like a likely thing to have been changed as the car is 31 years old. No telling who has done what to it in it's past.

Luckily, The low cycling switch on my Vette actually has an adjustment screw. So once I get it up and running, at least I can adjust the CCOT so the evap doesn't freeze up and it will cycle properly for the r12a.

Of course, I've got to getting it working first (even if it's "crappily") before getting to the switch adjustment.....
tourmax
Posts: 40
Joined: Wed May 13, 2020 2:26 pm

Re: 1988 corvette, don't understand what it's doing?

Postby tourmax » Fri Jun 19, 2020 2:45 pm

Ok, so....the new condenser showed up today.

I installed the condenser, then the new accumulator and went thought the rest of the system replacing all the seals. New orifice went in as well.

When I polished the compressor (took it apart to just the cases) it lost all it's oil. Same with everything else in the system. My 88 Vette takes 8 oz from dead empty. So I put 4 oz in the compressor. I was sure to put it in through the suction port and once the system was closed I made sure to rotate the compressor about 10 times in each direction (to be sure the oil wasn't going to "hydrolock" the compressor). Then I put 2 oz in the accumulator and 1 oz in the new condenser. That takes it to around 7oz, but since I hadn't touched the evaporator, I figure the evap is holding at least one (or two) ounces of mineral oil for a total of 8 oz in the system.

Pulled it down and it held vacuum fine. Pulled it down for 45 mins to get as much moisture out as I could.

Redtek recommends to NOT fill into a "hard" vacuum. So I let it loose it's vacuum and then hit the pump again. Pulled it down to about -14, which by definition is a "soft" vacuum.

Then I hook up the redtek and put one can in. Nothing. No surprise there, it takes two to do a fill comparable to the r12 fill. Second can goes in and things start to come alive. Compressor runs, but will short cycle. High side is going very high (350 +), the low side is also going high and there is no cooling. I grab the garden hose and run it over the condenser.

Instantly, things change. Low side settles around 35 psi. High side settles in just shy of 190-ish psi. High side lines are warm, low side lines are getting condensate on them. This is all still at idle (approx 750 rpm).

Ambient is 29c (approx 84 F) here today by the car temp display. I drop a thermometer in the main vent and it drops down to 11/12c (approx 51/52 F). So, 18c drop. Not too bad. Car is getting cold inside, even with the top down.

Bumping rpm up to 1500 rpm makes it start to cycle a bit. I adjust the cut out switch and settle on just a tick below 20 psi (redtek has lower head pressures than r12). The clutch will still occasionally cycle, but only when the rpms are up.

So it appears to be good to go.

One thing I did notice is the cooling fans (has a main and an aux fan) do not come on with the AC. I'll have to re-read my FSM, but I believe the fans are supposed to come on with AC selection. It would make sense for the fan to come on as sitting at a light or in slow traffic would mean no airflow over the condenser, thus, no cooling. So checking out the wiring and relays will be the next step to see what's up with those cooling fans....
Last edited by tourmax on Fri Jun 19, 2020 5:21 pm, edited 1 time in total.
tourmax
Posts: 40
Joined: Wed May 13, 2020 2:26 pm

Re: 1988 corvette, don't understand what it's doing?

Postby tourmax » Fri Jun 19, 2020 5:16 pm

Had supper and then took it out for a test drive.

Vent therm started at 35c. After a short drive up the street, the vent temp dropped to 11/12c. As soon as I was moving slow (or stopped) the vent temps would start climbing, once as high as 28c. Get rolling again and they drop right back down in the 11-12 range.

Get home and look it up in the FSM. Sure enough, the main cooling fan is supposed to come on with the AC. It's the electronic HVAC head and it's supposed to send a signal to the ECM, which turns on the cooling fan. The aux fan is "hard wired" to a relay and temp switch for the engine cooling.

I do a couple easy, first items on some of the trouble shooting charts. yep, cooling fan isn't coming on like it should. It comes on with the preset coolant temps, but not with the AC selection.

So it seems I'll have to get down into the wiring diagrams to figure out why the rad fan isn't coming on with AC selection.

We're headed to the cottage for a couple days, so it will have to wait until I get back.

But, the AC issues are getting run down. Pretty soon I'll have it done and nothing left to do but enjoy the Vette on some nice summer drives.

:)
B52bombardier1
Posts: 13
Joined: Sat Aug 31, 2019 6:21 pm

Re: 1988 corvette, don't understand what it's doing?

Postby B52bombardier1 » Sat Jun 20, 2020 5:13 am

I'm using a Four Seasons Fan Relay kit - part number 35879 - to make one of the E-fans on my 70 Chevy El Camino kick on the instant that the AC compressor clutch engages. This kit has a special compressor wire that overrides the wait time for the engine temperature to kick a fan on. This also helps avoid high head pressures at your compressor.

Amazon sells this Four Seasons kit and an Australian company sells what people say is a better kit (higher price) here:

https://daviescraig.com.au/product/digi ... v-24v-0444

I've had two of the Four Seasons kits running my E-fans with zero trouble. My E-fans are completely independent of each other for maximum cooling redundancy and get home dependability.

Rick
1970 Chevrolet El Camino 5.3 L LM7 Truck Engine & 4L60E Transmission
tourmax
Posts: 40
Joined: Wed May 13, 2020 2:26 pm

Re: 1988 corvette, don't understand what it's doing?

Postby tourmax » Sat Jun 20, 2020 11:33 am

B52bombardier1 wrote:I'm using a Four Seasons Fan Relay kit - part number 35879 - to make one of the E-fans on my 70 Chevy El Camino kick on the instant that the AC compressor clutch engages. This kit has a special compressor wire that overrides the wait time for the engine temperature to kick a fan on. This also helps avoid high head pressures at your compressor.

Amazon sells this Four Seasons kit and an Australian company sells what people say is a better kit (higher price) here:

https://daviescraig.com.au/product/digi ... v-24v-0444

I've had two of the Four Seasons kits running my E-fans with zero trouble. My E-fans are completely independent of each other for maximum cooling redundancy and get home dependability.

Rick

I’ve used similar stuff before. They work well for thier intended purpose.

But that’s pretty much what is Oem in my Vette already. Theres a fault in the system somewhere, I just have to chase it down and fix it.

Even though the fans are ecm controlled in my 88, they’re essentially “programmable” for me. I’ve got a Moates APU1 (http://www.moates.net/apu1-autoprom-pac ... l?cPath=64 ) hooked up to the ecm (ie: makes the obdI ecm “flash-able” like an obdII pcm) and fan temps are one of the editable parameters. I can tell it when I want them to go on/off and several other fan control options.

C4 Vettes went through several fan control schemes between 84-96. In my 88, the main rad fan is the one that the ecm turns on when it gets signal from the hvac controller (or temp signal from coolant sensor). The main rad fan is controlled by ecm, the aux fan is straight off an ect sensor in the block. So that narrows the problem of why its not coming on with ac selection to one system. I think it was 1990 the vette went to the ecm controlling both the rad fan and the aux fan. I can’t remember hie the fans were controlled before 1987-ish. I think the ecm still controlled the rad fan, ut the relay network was a little different. Don’t quote me on that though.

Now that I think of it, my rad fan might have been knackered for a while now as my ect will climb to around 235-240 before the fans kick on. Thinking about it a bit more, thats the temp that the aux fan is supposed to kick on. The rad fan is supposed to kick on somewhere around 225-230. So I may have more issues with the rad fan than I originally thought.

Then theres also the consideration that if/when I need parts to fix it, I can get them pretty much anywhere (gm, napa, scrapyard, etc). Thats a great thing if we happen to be out on a trip and the car breaks down.

Those fan control kits have some readily available parts (relays, connectors, etc) but also some pieces that might be a little bit harder to come by should they go “T’s up” on me....
tourmax
Posts: 40
Joined: Wed May 13, 2020 2:26 pm

Re: 1988 corvette, don't understand what it's doing?

Postby tourmax » Tue Jun 23, 2020 5:38 pm

Alrighty! last thing to fix has been identified!

My rad fan wasn't coming on with the AC on signal. My Vette has the electronic control head (very avaunt guard in 1988!) and when you turn on the AC it sends a signal to the ecm. The ECM is then supposed to increase idle speed and if the head pressure is over 233 psi, it turns on the main rad fan.

Someone in the cars past has done lots of "bubba" things to it, with the most heinous being in the electrical system.

Instead of fixing systems when they went down, they would steal power from other circuits, bypass things and just generally make a freaking mess in finding some redneck work around.

One of the "mods" I had to "de-mod" a while ago was someone had cut into the harness for the cooling fan to steal power from it. I can't remember exactly what they stole power for, but I had to cut it all out and solder the wiring all back together. It was done correctly when I fixed it as it's pretty hard to mess up color coded wiring, unless you're color blind I guess.... :?

So I started troubleshooting with the FSM, just to be thorough. I can do fine without a manual, but I have it here so why not follow it? It irritates me sometimes though, as you can tell it's meant to "simple simon" people with less that stellar mechanical/electrical skills through the process.

I go through all the checks and measurements and they all turn up good. Part of that is putting the gauges on to check the head pressure and it goes as high as 400 psi! Just below the high pressure cut out of 430 psi. But the fan still doesn't run with AC. No wonder the head pressure is so high. Then I pull the refridg pressure switch connector on the high side. That's the switch that controls the on/off for over 233psi/under 190 psi. As soon as the connector is pulled, the fan starts up (it's a NC switch) and the head pressure drops sub-200 psi. The vents go instantly frigid cold and the lines sweat up immediately (high humidity here today).

Yep, there's your problem! Seems like a U/S switch.

I plug the connector back on to the switch and the fan keeps running. I start to think I just had a corrosion issue on the terminals.

I turn the car off and then back on again. Cooling fan is dead again. Head pressure climbs like crazy. I pop the connector off and the cooling fan starts right up. I plug it back in and the fan keeps right on running.

Turn the car off and on again. Nope. Cooling fan is dead, head pressures headed for the sky. Pull the connector, fan runs, pressures drop like crazy. Plug it back in, fan keeps running. Turn the car off/on again and the cooling fan does the same "no run" thing.

So I figure the ecm must latch the cooling fan relay "on" until you turn the car off. Or the U/S pressure switch is just confusing the heck out of it. So a new pressure switch and should be good to go.

That is also the last "bubba mod" on the car, unless they intentionally hid more "butchery" under the interior carpet or something similarly stupid.....
tourmax
Posts: 40
Joined: Wed May 13, 2020 2:26 pm

Re: 1988 corvette, don't understand what it's doing?

Postby tourmax » Wed Jun 24, 2020 1:50 pm

Well, no one local could get the switch. Gm is no help, which is not a surprise as GM generally "abandons" any model over ten years old.

All the jobbers were a bust, or the costs (IF they can order one) were going to be in the $80-100range (welcome to Canada).

I ended up getting the part number off the switch and crossing it up on rockauto. 28 bucks gets me the right switch. Plus a bit of shipping cost.

So since I was already paying for shipping, I ordered up some replacement caps (missing my low side cap) in a valve servicing kit (new schraders as well), 2 more orifice tubes (just in case) and two more sets of system seals (never hurts to have extras around).

Until then, I think I'll just leave the switch disconnected. At least that way when I turn the AC on the fans will also start. I'll have to put up with the fans running when the car is up to speed, but only until the new switch arrives.

I can't swear to it, but I think I'll end up loosing my chrge when I swap out the switches. There may be a check valve in there, but I doubt it. the nipple that the switch screws on to is pretty small:

Image

It's the forward switch. But, looking at a line from a 92 indicates it just might be big enough for them to have put a check valve in there:

Image

Pics were both pulled off ebay.

When you blow that pic up, you can see what looks like a schrader valve in each port. We'll have to wait and see I guess......
tourmax
Posts: 40
Joined: Wed May 13, 2020 2:26 pm

Re: 1988 corvette, don't understand what it's doing?

Postby tourmax » Wed Jun 24, 2020 2:50 pm

couldn't wait to find out, so I spun the switch off the line. Thankfully, there was a schrader valve in there. The switch wasn't very tight, I could spin it off by hand. The switch was open to the high side pressure, as I go t a small "pssst" as I threaded the switch off.

So that pretty much confirms the switch is U/S. I had in the back of my mind that maybe the port was blocked, but that little bit of escaping refridg as I turned it off proved that wasn't the case.

So it's just wait for my parts order to show up and I can call the AC work done.


At least for the time being...... :roll:
davidh73750
Posts: 11
Joined: Tue Jul 07, 2020 4:11 pm

Re: 1988 corvette, don't understand what it's doing?

Postby davidh73750 » Wed Jul 08, 2020 5:13 pm

Have you got it back together yet? . Good information when narrowing things down.

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