AC compressor/clutch ground?
#16
Three Wheelin'
Thread Starter
At this point now that you describe a problem with the AC operation,
I am with Dave and Fred the HVAC head needs a relay refresh,
while your in there replace the freeze switch and install a 3 amp fuse at the freeze switch
NOTE Greg Brown rebuilds these and makes sort of a kit to refit this HVAC system
I am with Dave and Fred the HVAC head needs a relay refresh,
while your in there replace the freeze switch and install a 3 amp fuse at the freeze switch
NOTE Greg Brown rebuilds these and makes sort of a kit to refit this HVAC system
not familiar with how to install 3 amp fuse at freeze switch. is there a thread about this? or can you explain?
#17
Team Owner
unplug one of the wires at the freeze switch,
and plug the wire onto a 3 amp fuse ,
make a short wire with 2 female spade connectors,
connect one side to the other leg of the fuse and the other to the freeze switch
and plug the wire onto a 3 amp fuse ,
make a short wire with 2 female spade connectors,
connect one side to the other leg of the fuse and the other to the freeze switch
#18
Rennlist Member
You can add a booster relay over at the freeze switch. A nice little square 5-10 amp relay, wired so it will fire when the head unit relay closes, and let THAT gate the current for the AC compressor clutch. Then the HVAC unit stops going bad because it only has to switch a couple of dozen milliamps to close the bigger relay.
Simple fix, I documented it in some other thread, works well, worth a shot.
Simple fix, I documented it in some other thread, works well, worth a shot.
#19
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The anti-freeze switch functions intermittently. That’s is JOB. When it goes on strike it doesn’t open the clutch a/c circuit. When this happens the evaporator ices up and both air flow and vent temperature are negatively affected. And the vents will usually spit a little water at you when this happens.
Use a *4A* fuse in the a/c clutch circuit in a Weather Pack (or similar) in-line fuse holder.
I just love non-stock wiring with extra relays stuck in random places all over the car: makes it SO easy to diagnose problems when your wiring diagrams have nothing to do with the car.
Use a *4A* fuse in the a/c clutch circuit in a Weather Pack (or similar) in-line fuse holder.
I just love non-stock wiring with extra relays stuck in random places all over the car: makes it SO easy to diagnose problems when your wiring diagrams have nothing to do with the car.
#20
Team Owner
hopefully the owner will add a supplement page to the owners manual describing electrical modifications
i know thats a stretch, but they do this when mods are done to aircraft
i know thats a stretch, but they do this when mods are done to aircraft
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#22
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Oh foo. The original relay was far too small and Porsche should have known it. Hacking a large relay onto the side of the HVAC unit is complicated at best, and would damage the vias and pads at worst. Maybe there is an infinite supply of HVAC heads, not sure.
Putting a booster relay at the freeze switch requires NO wire cutting, no taking apart of the HVAC box, one relay, and a total of three net wires with an inline fuse: One going to a +12 source in the engine compartment, one going to the nearest bolt for a ground and one to connect the freeze switch male to the relay's NO male.
Your mileage, as they say, may vary. But it's a pretty simple and effective fix to a very annoying design flaw.
Putting a booster relay at the freeze switch requires NO wire cutting, no taking apart of the HVAC box, one relay, and a total of three net wires with an inline fuse: One going to a +12 source in the engine compartment, one going to the nearest bolt for a ground and one to connect the freeze switch male to the relay's NO male.
Your mileage, as they say, may vary. But it's a pretty simple and effective fix to a very annoying design flaw.
#23
Oh foo. The original relay was far too small and Porsche should have known it. Hacking a large relay onto the side of the HVAC unit is complicated at best, and would damage the vias and pads at worst. Maybe there is an infinite supply of HVAC heads, not sure.
Putting a booster relay at the freeze switch requires NO wire cutting, no taking apart of the HVAC box, one relay, and a total of three net wires with an inline fuse: One going to a +12 source in the engine compartment, one going to the nearest bolt for a ground and one to connect the freeze switch male to the relay's NO male.
Your mileage, as they say, may vary. But it's a pretty simple and effective fix to a very annoying design flaw.
Putting a booster relay at the freeze switch requires NO wire cutting, no taking apart of the HVAC box, one relay, and a total of three net wires with an inline fuse: One going to a +12 source in the engine compartment, one going to the nearest bolt for a ground and one to connect the freeze switch male to the relay's NO male.
Your mileage, as they say, may vary. But it's a pretty simple and effective fix to a very annoying design flaw.
#25
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If the relay was far too small it would not have worked for 25 years or whatever.
Seems to me it may arguably have been a bit on the marginal side and as the relay performance degrades with age it reaches a point where it can no longer function reliably. No great rocket science here- just common sense.
Seems to me it may arguably have been a bit on the marginal side and as the relay performance degrades with age it reaches a point where it can no longer function reliably. No great rocket science here- just common sense.
#26
Drifting
Threading the tube through to the evaporator is easy. You just need to be careful not to stress that capillary tube too much as you handle it, so as not to break it off at the freeze switch. From memory the switch is held on by a single bolt to a bracket.
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If the relay was far too small it would not have worked for 25 years or whatever.
Seems to me it may arguably have been a bit on the marginal side and as the relay performance degrades with age it reaches a point where it can no longer function reliably. No great rocket science here- just common sense.
Seems to me it may arguably have been a bit on the marginal side and as the relay performance degrades with age it reaches a point where it can no longer function reliably. No great rocket science here- just common sense.
What I can tell you is that for 928s that I get that have a full from-new service history I see a lot of in-warranty HVAC head replacements. Of course I don't get many of those kinds of 928s. Maybe 6 to 8 total over 20 years. But, I've seen three documented in-warranty HVAC head replacements. One of those was my '91 GT.
Putting a booster relay at the freeze switch requires NO wire cutting, no taking apart of the HVAC box, one relay, and a total of three net wires with an inline fuse:
One going to a +12 source in the engine compartment, one going to the nearest bolt for a ground and one to connect the freeze switch male to the relay's NO male.
Yup. You just have to have some skill with the soldering iron. While I have a stick of the small 5A relays, I do not have the skill with the soldering iron. One of these days, when I'm bored I'll practice enough to do the relay R&R myself.
Replace the relay in the head unit, put a 3 amp fuse at the freeze switch and forget about it for 30 years.
Let's also cover why the in-line fuse is such a good idea: The on-HVAC-board relay is not a fuse. If the A/C mechanically seizes and current goes infinite, the relay (any size) might act as a fuse. Or the PCB in the head might be the 'fuse.' The former is repairable. The latter not so much.
and don't just shove it in like you would a long sword into a scabbard. Some folks have managed to put a hole in the evaporators when doing this. Do it with some delicacy.
#28
Three Wheelin'
Thread Starter
going slow, one question at a time: in installing the 4 amp fuse for the freeze switch, do I splice this into the wire that goes forward to
the pressure switch, or the wire that goes rearward to the control unit?
the pressure switch, or the wire that goes rearward to the control unit?
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https://www.amazon.com/Fastronix-Automotive-Marine-Weatherproof-Holder/dp/B01LWNVT61/ref=sr_1_4?keywords=weatherproof+fuse+holder&qid=1548023347&sr=8-4
crimp a male spade on one lead and a female spade on the other. Put a small slice of heat shrink on the female. Unplug one side(*) of the anti-freeze switch and plug in the fuse holder between the switch and the lead you unplugged.
(*) Doesn’t matter too much which side.
#30
Three Wheelin'
Thread Starter
^^^^got it. did not mean to use the word "splice"
dave: you are saying you have a 5 amp retrofit relay that fits the footprint of the original? is this something I can find at mouser or other supply house?
also, the dr bob write up suggests a 10 amp external: is it "better" to find a 5 amp external? or better if I could find a 10 amp internal? not comprehending
why its "best" to use a 5 or 10 amp?
dave: you are saying you have a 5 amp retrofit relay that fits the footprint of the original? is this something I can find at mouser or other supply house?
also, the dr bob write up suggests a 10 amp external: is it "better" to find a 5 amp external? or better if I could find a 10 amp internal? not comprehending
why its "best" to use a 5 or 10 amp?