AC 101 Help with the 924S

[austinporsche]

Hi all.

Having bought a 1988 924S almost 2 years ago, then putting it into storage, I have finally taken it out to drive it.

First, among my running 2 seaters (911T, RX7, X19 -- as well as the 914 I had in my twenties), let me say that the 924S is already my favorite. Ergonomically, everything is where it should be, the engine pulls stronger than its 158hp would indicate, the gear spacing is right on and the handling is very neutral and predictable. Would it be presumptive of me to say the 924S is perfect?

Problem is that I live in Texas, and without working AC, the car's use is limited to 3-4 months -- and I want to make this into my daily driver.

I am pretty good at AC basics. OK, more than basics, I have replaced compressors, condensers, accumulators, expansion valves, hoses and even evaporators (the worst job ever), flushed systems, done full vacuum pump downs and refills, etc. I have all the tools.

In most all other cases, I haven't even needed a schematic to figure out the flow of things, but the 924s has me a bit befuddled.

I have the Haynes 944 manual (I have 4 944s, none running, all waiting to be restored -- there is no 924 manual correct?), but the Hayne 944 AC section is pretty useless save for the electrical schematics for the AC. (Even that schematic is confusing to me; for example, what is the air conditioner supplementary air valve?)

So first question is whether anyone has a proper service manual or even parts manual that shows an exploded view of the AC system so I can sort things out, like where the expansion valve is (I am assuming since it is not at the firewall, that it is inside the cabin with the evaporator).

Second thing is figuring out the high and low sides. There are two ports: one at the firewall and the other at the receiver/dryer. The one at the firewall has an R12-to-R134 low side quick connect adapter on it and both have blue caps (2 low sides? me thinks not). The blue cap on the port at the receiver/dryer notwithstanding, am I correct to assume the port at the firewall is the low side?

I got the gauges out (my R12 set; I also have an R134 set so I can keep the oils separate without having to clean it every time I move from a 12 system to a 134 one), connected to the firewall adapter and pumped in Redtek R12a (that bridge refrigerant that works in both 12 and 134 systems: great stuff when you are unsure whether an original 12 system has been upgraded to 134).

It gets up to 30-40psi, then I can hear a hiss: clearly there's a leak in the hoses running along the firewall or (dreaded) in the cabin behind the dash. (dash is cracked and needs to be renewed anyhow).

It is tight as heck and like spaghetti there at the firewall, and one hose to/from the evaporator has a coupling on it while the other doesn't, so again an exploded view of how all the plumbing is routed would be most helpful to get me on my way.

Thanks in advance for any help.

[djnolan]

On the 944 there are several different line and fitting configurations. The high side is the smaller of the two lines and the r/d is on the high side.

I have successfully retrofitted two 944 cars by changing the fittings, adding 3 OZ of ester oil, running an evac and go. No need to change out the lines, seals, or oil.

You could also add BG frigiquiet to improve the performance.

[mattdavis11]

Sounds like someone has messed with the system before. Low side should be on the compressor, high side near the drier/headlight.

Anyway, if you say you have a low side service port at the firewall, the line must have been adapted/repaired in the past.

I don't have a diagram of the system, but if you have done a/c work, you should know what is what, these cars are not special. Expansion valve is inside the car, behind the dash, inside the evaporator case.

When you find the issue, which I gather is a line leak, call Rick at Austin Rebuilders, 512-448-0884. He can take care of the lines, rebuild the hoses, etc.. Tell him Matt at 1800 sent you.

I'd help you out but recently moved out of Austin to Seguin. If you want to bring it down here, you can look at my 83, should be the same set up.

Good luck! And I am an a/c guy.

[Pauld_94S2]

First, go here and download the workshop and parts manuals, drawings will help you sort out locations and part numbers:

Porsche 944 manuals - Free download

There is a lot of things to know about automotive air conditioning systems, but you appear to have knowledge and I'll leave it at that.

Having said that, here's my help in a condensed form:

For the leak, start with a visual inspection of the hose from the compressor to the condensor, it's the most stressed part. Look for oily parts where leaks are. Replace the O-rings at the hose fittings if you open it.

If you see any debris, metallic particles, or anything other than refrigerant oil in the system, please flush the system thoroughly so you don't wind up doing the work over again.

Best setup is to pull compressor and drain oil out, add 2-3 ounces of POE (POE will mix with mineral oil (R12 oil) and DON'T use PAG). Replace the drier and add 3-4 ounces of POE to it. Be sure to hand rotate the compressor in both directions several turns after adding the oil so you don't lock it up. Use new O-rings at hose block.

Evac the system properly, and add R134a to 80% of the oil volume in ounces that R12 system uses, or if you are experienced, use your gauges to go by temperature and pressures. Don't overfill with refrigerant, less is better. Add refrigerant slowly to allow it to mix and distribute the POE oil. There are You-tube videos if you want more info.

Seeing less than 45 degrees out the middle dash vents with the fan set on mid speed is easily doable. Typical can be 38-42 degrees at 2500 RPM.

Good luck, take your time and do it right!

If you need hoses or other parts, or a good guy to talk it over with, call Charlie at Griffiths:

https://griffiths.com/porsche/air-conditioning/924-944-951-968/

And here's a link to practices in MVAC:

https://griffiths.com/warranties/

[irish44j]

Originally Posted by mattdavis11

Sounds like someone has messed with the system before. Low side should be on the compressor, high side near the drier/headlight.

Anyway, if you say you have a low side service port at the firewall, the line must have been adapted/repaired in the past.

.

Nope, my '87 924S also has a low side port at the firewall (plus one on the compressor). It definitely makes things WAY more convenient. I can't see any indication that it's "aftermarket" or anything - so may be something that was only put on some cars, and not on others. The '88 924S parts shell I had also had that fitting on the firewall.

[onZedge]

My 87 924S has the low side fitting on the firewall as well.
I flushed out the entire system and replaced ALL the o-rings, including re-sealing the compressor (compressor body o-rings were the culprit leak). Griffiths has the compressor body o-ring kit.
It's been 2 years since the reseal now, and even with R134a, the AC works just fine during the recent 95 deg weather we've been having.
The only ouch was the $700.00 for a new evaporator. The PO's AC tech used the wrong (longer) screw for the bracket that holds the hoses to the rear of the evaporator box and punctured the evaporator!

[austinporsche]

Thanks everyone so far, and esp. Mattdavis11, for the advice, local AC hose builder contact and offer to help and Irish44j for confirming that there is a low port at the firewall (though it is on a "skinny pipe"). I figured the port at the receiver was high side, the blue cap notwithstanding (I'll bet when whoever put the R12-to-R134 quick connect conversion on, they took that R12 blue cap and put it on the R12 schrader at the receiver to replace a missing red one).

I put positive pressure into it yesterday -- I am in AC hell this week, helped my brother completely flush and rebuild the AC on his 2000 1500, what a breeze -- and I swear I can hear a faint "hiss" somewhere in the engine compartment between the firewall and the compressor, along driver wheel well or up by the receiver/dryer (which has need been opened -- it still has red paint dabs on the fittings).

FYI, per advice of another forum member, I tried to test the compressor clutch by bypassing the lower pressure switch with a jumper (from the black/white wire connector on one side to the combo black and brown (ground?) wire connector on the other -- the electrical schematic shows only a black wire), but nothing happened, so maybe I have a couple of things going on here -- electrical and mechanical.

How hard is it to access the evaporator and the line fittings to it and the expansion valve? Does the dash need to come out? (glovebox is already out to get at AC amplifier and the relays). Dash is cracked and needs renewed anyhow, so maybe an opportunity to lay it up for a while and get it all done at once.

Maybe a complete renewal of the system (other than the evaporator) is in the cards for me. Mark, I get down your way on occasion, maybe you can take a look?

Anyhow, like Mark Watney in the Martian advised:

At some point, everything’s gonna go south on you… everything’s going to go south and you’re going to say, this is it. This is how I end. Now you can either accept that, or you can get to work. That’s all it is. You just begin. You do the math. You solve one problem… and you solve the next one… and then the next. And If you solve enough problems, you get to come home (or get to have AC). All right, questions?

[austinporsche]

Paul94S2, thanks for the step-by-step. You're suggesting that I do a full flush and upgrade to R134, right?

And other than the POE (not familiar with it, but will look it up), no need to change expansion valve, compressor, etc?

And in lieu of R134, have you ever tried the butane-based R12a from Red Tek?

On a lark, without any diagnosis, I just pumped a can of this stuff into a non-working and empty AC system on an '82 RX7 I also own, and viola, 38 degrees at the center vent at 95 degree ambient.(like the 924, got a deal on it, then put right into storage for a couple of years -- and like the 924, the low side port had been upgraded with an R12 schrader-to-R134 quick connect adapter). First time something ever worked better than advertised for me.

[Pauld_94S2]

YES = You're suggesting that I do a full flush and upgrade to R134, right?

Flush as best you can tolerate, very little oil is in the evap or lines, places are compressor, drier, and condensor. Use R134a, it's cheap, it works, and it doesn't fractionalize.

CORRECT = And other than the POE no need to change expansion valve, compressor, etc?
You can use all of the same parts and compressor, just replace the drier because you are changing the oil.


YES = And in lieu of R134, have you ever tried the butane-based R12a from Red Tek?
OK to use, but long term go R134a.
https://www.achrnews.com/articles/82752-blends-101-an-introduction-to-refrigerants

Now go gitt'r done!

[onZedge]

Originally Posted by austinporsche

...How hard is it to access the evaporator and the line fittings to it and the expansion valve? Does the dash need to come out? (glovebox is already out to get at AC amplifier and the relays). Dash is cracked and needs renewed anyhow, so maybe an opportunity to lay it up for a while and get it all done at once.

This looks worse than it actually is - take a few cell phone shots as you disassemble to remind you how things go back together later. I added a dedicated fusebox for the audio system, so your stock wiring won't look quite as complicated.


The evaporator/blower lives behind the glove box, and the expansion valve lives inside - follow the top line to the back

[Pauld_94S2]

Your original post has me confused.

You are chasing a bad relay under the dash and guess the control knob isn't working, but you state that when you added refrigerant, you could hear a hissing noise and the refrigerant pressure went down.

Clearly, you have a leak you need to repair.

It will be difficult, but follow the hose from the compressor and condensor along the fender well and firewall to where it goes through the firewall to the evaporator. Look, or feel, for a presence of oil along the lines.

Somewhere, if there is a leak in this area as you state, you will feel an oily spot, most likely where the rubber hose is crimped to the hard line, or the rubber hose is broken through the outer jacket.

Since you don't state you have a refrigerant leak sniffer, this is the only way you can find the leak.

Also, have you downloaded the manuals and reviewed the MVAC system?

This is an HVAC system in a Porsche.
It's the same as any other car.
Basic AC troubleshooting applies.

[88Silver924S]

If you drop the evaporator down from under the glove box for any reason you may want to take the opportunity "while-you're-in-there" to install new heater hoses.

A few years ago I took the dash apart on my '88 but still could not access the hose clamps for the two heater hoses. I suspect the only way to access the hoses and clamps at the heater core inside the cabin on the 924S is when the evaporator is removed.

Good luck and have fun.

[onZedge]

Originally Posted by 88Silver924S

...I suspect the only way to access the hoses and clamps at the heater core inside the cabin on the 924S is when the evaporator is removed...

Not the only way: you can leave the evaporator assembly where it is and remove the dash instead!!!

...but that opens up a whole new chapter of "while-you're-in-there"...

[88Silver924S]

I had removed my dash and as I recall (it was a few years ago) the heater hose clamps were still not accessible on my car with the dash removed; the evaporator was in the way. I didn't remove the heater unit though. Maybe disconnect the hoses in the engine bay (or cut them) and pull them through the firewall still attached to the heater core? I'm still running the original heater hoses.

[onZedge]

Originally Posted by onZedge

...but that opens up a whole new chapter of "while-you're-in-there"...

Yes, removing the heater/air flow control box is in the above "chapter". Replacing all the flow control box damper foam seals with silicone sheeting is in there also. IIRC, somebody here or RL had a great write up with lots of pictures...