924Board.org

[-nick]

I've seem this question come up a number of times. I don't know that I've seen anyone else who has actually done the swap, so here's my writeup.

Parts you need from a 944 (82-85.1) or 924S (87-88 ) that are different than early 924:
- big r2d2-looking heater box under the dash
- mount for heater box (under dash)
- heater/radio center console and attached gauge panel
- heat controls - slider assembly / fan speed switch & pigtail harness
- blower motor cover (under the hood)
- heater core
- under-dash ducting / vents
- coolant control valve

The big difficult part is that the later heater box hole in the sheetmetal (between the interior and under the hood) is moved 1/2" forward compared to the 924 hole. I dealt with this by cutting a box around the hole, then cutting a 1/2" strip off the front of the box, then reinstalling the box (now 1/2" forward) with the 1/2" strip put in the rear of the box. See the pic:




Next tack weld as much around the perimeter of the box as possible and fill in the remaining gaps with welds if you can or fiberglass/bondo for what you can't. Unfortunately, it's just too tight to weld around much of the area. Now everything lines up perfect and the 944 heater box will slide right in.

The plastic cover over the heater blower motor under the hood will need to be cut in the back in order to clear the windshield wipers. The potential for rain to leak in from around this cover is _very_ high, so test that you're water tight afterward.

After crossing that hurdle, the rest of the parts just bolt in place.

The heater core is another slight trick - the hose diameter for the 944 core is larger than the 924 heater hoses. Plus, the 944 core hose barbs don't protrude through the firewall like the 924 core. My solution was to use a brass female-female hose barb to lengthen the stock 924 heater hoses and plug them into short pieces of hose on the 944 core. It's messy, but works. If you can find stock 924 heater core hoses that are about 2-3" longer on the core side, then let me know!

The coolant valve is the last trick. It also uses a larger diameter barb. If your hoses to it are new and soft, you can push them on by lubing the insides with a tiny film of grease. Also _make sure_ that the flow of coolant through the valve matches the directional arrow. If you put the valve in backwards its seals will blow and you'll have hot coolant circulating through the core all the time.

The last thing is to wire up the switch for the heater blower motor. This is pretty straightforward. The only thing to note is to make sure and use switched +12V for the power supply. When the switch is turned to the "off" position, the fan still rotates very slowly to circulate air in the cockpit. Therefore, the blower is never off unless the key is off.
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

[BionicBalls]

I'm currently undertaking this project so I decided to add some tips I've found as I go. First, the problem with the hoses not reaching is no problem. Just pull the heater core out of your 924 and put it in your 944 unit. There is a panel that holds them in, and it can be a little PITA to get out, but a straight edge screwdriver will take care of it.

More tips as I get further along. I'm currently trying to figure out if I can incorporate the 944 A/C setup at the same time. Only big benefit of the 944 A/C unit is that it will cut off the heater via vacuum when A/C is turned on.
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1980 924 NA
1982 931

[BionicBalls]

Another breakthrough today:

I'm not sure what Nick was looking at, but upon test fitting the heater box.. it doesn't look like there is any need to cut the heater opening and move it forward 1/2". Mine lines up great. The cowl panel is shaped a bit differently on the 944's, but it is flimsy metal that can be cut and shaped to provide clearance for the squirrel cage blower to fit in and the cover to sit nicely against it.

I'm finishing the conversion up tomorrow, I'll take some pics then. Since the opening doesn't need to be moved forward, this is a pretty simple conversion. Pretty much bolt on. Only real fabrication is to the cowl panel and then drilling some holes for the heater box to mount to... The 944 unit uses 4 bolt holes whereas the 924 unit uses a protruding arm that fits in a cubby on the backside of the firewall from the coil.

The only reason the conversion is taking me 3 days is that I also cut out and made a new battery tray and the lower part of the frame rail in the same area. I also cleaned up the grounds, eliminated some unneeded wiring, am adapting the 944 A/C unit (not hard will elaborate in a sec), and am wiring in a self-dimming rear view mirror from a Cadillac.

The 944 A/C unit is almost identical to the 924 unit except for the 2 relays and vacuum fittings it uses to open and close the A/C when it's in use at the same time as the heater. These relays have 5 wire coming from them, 3 of them match up to the existing 924 wires. All I have to figure out is what the other 2 wires are for, but I suspect that they are power and ground for the second relay. I'll figure that part out tomorrow.
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1980 924 NA
1982 931

[tyfighter123]

Im looking to do the samething here soon. Looking forward to the pictures and write up.
_________________
Porsche 924 1977 N/A
Mustang GT/CS 2007
Porsche 924S 1987 (parts car)(cut up and recycled)
Porsche 911S 1976
Porsche 931 1980
Porsche 931 1980 (parts car)

[BionicBalls]

Came so close, and then had to redo it all. My test fit looked good, but upon actually fitting it it doesn't work. You have to do the cutting and welding as nick described. you also have to use the 944 heater core, that ended up being the root of all my problems.

One thing I did find that does actually work is a hose to use. As Ncik described, the heater hoses are about 2 inches too short to fit through the firewall and attach to the 944 heater core. The bottom one can be stretched and made to fit, but the upper one's strange shape makes this impossible. NAPA sells a hose #11048 that work perfectly though. You have to trim about 1 1/2" off the smaller diameter side, but otherwise works like a charm.
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1980 924 NA
1982 931

[ksis]

Looks like alot of work. Is there any suitable substitute for the blower motor?
Ihave been following this and doing research. The motor in my 924 was replaced but is very loud.
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77 924
64 Spitfire
76 TR6
04 Jetta
77 Schwinn Scrambler
Awsome pair of Chucks

http://www.cardomain.com/id/ksiskin

[BionicBalls]

I finished the conversion tonight. Anybody looking to do it, I would not recommend converting the A/C unit as well unless you like wiring. You have to run quite a few new wires and add a fuse and 2 extra relays. In hindsight I wish I would have taken the time to pull the entire A/c harness out of the 944 uncut. Oh well, it's done now and everything works great. I even have things working in my car that weren't before since I cleaned the grounds.
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1980 924 NA
1982 931

[tyfighter123]

How did you end up doing the heater and ac? Pics?
_________________
Porsche 924 1977 N/A
Mustang GT/CS 2007
Porsche 924S 1987 (parts car)(cut up and recycled)
Porsche 911S 1976
Porsche 931 1980
Porsche 931 1980 (parts car)

[BionicBalls]

BE AWARE: the 944 coolant flows an opposite direction than the 924. This is important for the Heater Control Valve. On the 944, the HCV is located on the heater core inlet hose. It is located on the heater core outlet hose on the 924.

I found this out the hard way, which is often the case. New HCV is ~$17 from Pelican. Seals will blow if put in backwards and you will leak coolant from the lever.

In case you still don't know which direction to point the arrow, point it toward the engine and away from the firewall.
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1980 924 NA
1982 931