A/C Upgrade Project starts tomorrow!

[GH85Carrera]

Last Summer I drove my 85 911 to Savannah GA in AUGUST. On one day-tour on the way to lunch my wife actually asked me to turn the temp up. When I drove to Roebling Road for the DE I knew it was going to be a brutal hot day. I had the AC cranked up to max to soak up as much cool as possible on the trip from Savannah to Roebling Road. I got there in the morning and the roof of the car on the outside was covered in moisture. My 911 looked like a big white beer can that just came out of the fridge. It was covered in condensation. My glasses instantly fogged up when I stepped out of the car.

The AC was tested to the max on my trip home to Oklahoma. We were driving due west for many hours in the afternoon and it was 105 outside. The sun was shining into our faces and we could feel the heat of the sun on our chest. The AC kept us reasonably comfortable.

I have the system from Griffiths. 4 total condensers and the new evaporator, and all new hoses running R-12.

[wwest]

Originally Posted by Paul K

Mitch:

I do have the Bentley manual. I was hoping for a quick 'Red & White wire to terminal 87' answer from Griffiths, but instead they sent me a wiring schematic which doesn't answer the question, as I still don't know which wire goes to which terminal.

Thanks,

Paul.

Nyssa...?

[Mitch Leland]

Paul,

Did you figure out the replay wiring? I'm sorry I was gone most of the day, then got into something else when I got home.

[Paul K]

Originally Posted by Mitch Leland

Paul,

Did you figure out the replay wiring? I'm sorry I was gone most of the day, then got into something else when I got home.

Mitch:

No luck as yet. Wires are yellow, black, red and red/white stripe. Terminals are numbered 85,86,87 & 30.

I'm going to tackle the upgrade of the box thingy in the smugglers box this weekend. Seems like that's the most complicated part?

Thanks,

Paul.

[hcoles]

Originally Posted by Paul K

Mitch:

No luck as yet. Wires are yellow, black, red and red/white stripe. Terminals are numbered 85,86,87 & 30.

I'm going to tackle the upgrade of the box thingy in the smugglers box this weekend. Seems like that's the most complicated part?

Thanks,

Paul.

relays are hooked up like this, I call the two circuits the trigger side and the power side

[Barrpete]

Here's a link to an '82 SC AC wiring diagram from Pelican's Tech Info Center:

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_AC.jpg

It shows a relay with the same colored wires, 87-red, 86-yellow, 85-black and 30-red/white stripe.

You may already know this, but be careful with the white "wire" that goes into the top of the evaporator housing. It's actually not a wire at all but a tube that's part of the temperature switch. If you kink or break it you'll be looking at replacing that switch as well.

[Paul K]

Originally Posted by Barrpete

Here's a link to an '82 SC AC wiring diagram from Pelican's Tech Info Center:

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_AC.jpg

It shows a relay with the same colored wires, 87-red, 86-yellow, 85-black and 30-red/white stripe.

You may already know this, but be careful with the white "wire" that goes into the top of the evaporator housing. It's actually not a wire at all but a tube that's part of the temperature switch. If you kink or break it you'll be looking at replacing that switch as well.

Originally Posted by hcoles

relays are hooked up like this, I call the two circuits the trigger side and the power side

Thanks guys! I did read about the 'white wire' and have been very careful with it!

[86 911 Targa]

Originally Posted by Paul K

Mitch:

No luck as yet. Wires are yellow, black, red and red/white stripe. Terminals are numbered 85,86,87 & 30.

I'm going to tackle the upgrade of the box thingy in the smugglers box this weekend. Seems like that's the most complicated part?

Thanks,

Paul.

If you replace the relay, get the fused one from our host.

[86 911 Targa]

Here's a pic. & CKT Diagram.

The color code is at the bottom of the CKT diagram.

Good luck,

pm me as needed.

Gerry

[Mitch Leland]

red/wht - 87
red - 30
blk - 86
yellow - 85

See page 970-47 in Bentley's...

[sacoffee]

I pulled the evaporator box to inspect and clean while the AC system was down to replace the compressor.

Sure glad I did because the PO mechanic wrecked the install when he replaced the expansion valve. Fins were bent, thermo wire wasn't installed, no clips on the box so there wasn't a good seal. Also the evaporator rubber seals were toast.

I also found that he had cut the copper probe short, luckily I had a spare thermo wire with the right length copper sleeve and got it in at about 79 deg angle down in the core.

Looking at other threads I decided to fab my own plastic block off plate to ensure air is sucked thru the coils and not around the sides.

[Discseven]

Nice idea on the evap seal Steve. I forgot the way the system sets up --- can this be done without disconnecting lines?

[sacoffee]

Hey Karl, it could be done without disconnecting the lines. You would have to lift the evaporator and slide it in. But I was an idiot for not taking dimensions,

[sacoffee]

Installed new motor and evaporator, here's the cut out dimensions

[azhodge]

Originally Posted by tsuter

Another note I've not seen much is MAKE sure your new expansion valve was set for R134A not R-12.

With R134A you want low side pressures of 18-20psi to get really cold. That control comes from the expansion valve adjustment. If it was set for R-12 you'd see 28-30 low side PSI and get only 40+F or so at the vents w 134a.

So whoever sold you that valve make sure it was set for R134a not R-12. And if they say its the same or doesn't matter you should get it somewhere else.

This was an interesting quote. In conflict with others. could it be true. A big deal if it is.

[kuehl]

Ideally, you do not want any liquid refrigerant returning to the compressor otherwise the liquid could ‘slug’ or damage the compressor. Typically, in ‘normal conditions’, this does not happen in a 911/930 because of the long run between the evaporator in the front smuggler’s box and the compressor in the rear engine bay; the hose between, 12ft+, absorbs ambient heat and tends to vaporize any remaining liquid.

Assuming ‘superheat of the evaporator’, meaning all of the liquid refrigerant has turned to vapor by the time it exists the evaporator outlet. To determine the ‘superheat’ you would note the temperature of the evaporator outlet, ie. 32F, and the pressure at the evaporator outlet, ie. 20 psi, look up the pressure-temperature correlation for R134a, 20 psi=23F, subtract the evap outlet temp of 32f by the P&T of 23F and you’d have 9F of superheat. However, the issue for a DIY to obtain the low side pressure is that they are measuring this back at the compressor rather than at the evaporator outlet which would require a service fitting at the evaporator outlet connection.

The pressure taken all the way back at the compressor inlet tends to be lower than at the evaporator outlet because of further heat absorption and friction along the way. Hence, there would be a lower psi reading at the compressor as compared to the evaporator outlet.
For example, assume the evaporator outlet is actually 30psi (on a PT chart = 35F) while the compressor is 20 psi (on a PT chart = 23F) the difference could be:
32F - 35F = -3F or
32F - 23F = +9F superheat.

Inserting a temperature probe inside the evaporator core can tell you a lot as to what is going on. If your thermostatic probe (the aluminum capillary tube sensor from your thermostat) is making good contact inside evaporator core it should be turning off the compressor when things get too cold.

PS: Ignore Willy, he is just going to mess up the thread

[Pazuzu]

Originally Posted by kuehl

However, the issue for a DIY to obtain the low side pressure is that they are measuring this back at the compressor rather than at the evaporator outlet which would require a service fitting at the evaporator outlet connection.
.

Good info. If someone (like me) was building a new system right now with costom hoses (like me), and was willing to put an service port fitting on the evaporator exit, would it be worth it? Would such info help everyone else to know if the R12 vs R134 expansion valve is an actual issue? Would the superheat value give a better idea of a full charge that the pressure at the compressor? Where can one find the P-T relationship for R134 (is it the standard chart that I see everywhere)? And finally, what would be the optimal superheat for our system to work for? 9 degrees? 11 degrees? What is optimal?

Since, you know, someone might be willing to actually check this...

[wwest]

Originally Posted by Pazuzu

Good info. If someone (like me) was building a new system right now with costom hoses (like me), and was willing to put an service port fitting on the evaporator exit, would it be worth it? Would such info help everyone else to know if the R12 vs R134 expansion valve is an actual issue? Would the superheat value give a better idea of a full charge that the pressure at the compressor? Where can one find the P-T relationship for R134 (is it the standard chart that I see everywhere)? And finally, what would be the optimal superheat for our system to work for? 9 degrees? 11 degrees? What is optimal?

Since, you know, someone might be willing to actually check this...

Absent a restriction to flow somewhere in between, it doesn't seem possible to have different pressure at the evaporator outflow vs the suction line at he compressor.

Different temperatures, yes, but pressure anywhere in the return hose "volume" will be equal to the average temperature.

[Pazuzu]

Originally Posted by wwest

Absent a restriction to flow somewhere in between, it doesn't seem possible to have different pressure at the evaporator outflow vs the suction line at he compressor.

Different temperatures, yes, but pressure anywhere in the return hose "volume" will be equal to the average temperature.

That seems to fly in the face of every fluid dynamic rule out there, but we'll ignore that.

We won't ignore that he also made it clear that the pressure change is attributed to the temperature change across 12-15 feet of hose...which is something that you hold near and dear to your heart, and would NEVER refute, right?

[ganun]

Yeah Mike, a port there would be cool, just to know. I suspect that just a few degrees like 5, certainly less than 10 is all one would want. How about it Kuehl?