A/C and Heating problems relay R14

dporsche74 · 12:18 PM

Got a 1990 964 C4 ..

First .. the A/C was not working when i picked it up and heat was working fine

So...I got a new a/c condenser.. new ballast resistor
.. new R14 relay's .
I took it to the shop for the R134 conversion.. they tested it and filled it
pressure is good. high and low side.

The strange part is... With the R14 relay installed the a/c doesnt get cold.
the condenser fan cycling on and off .. Heat willl not work . (blower cycles on and off and no heat) . I see the mixture servo working back and forth cycling and no heat ) Oil cooler fan is doing the same thing on off cycle..

So...I pull the R14 relay out.. leave it empty .. the A/C is working nice and cold
Heat is working.. get hot and fresh air working normal . oil temp temp is low

Everything works like it should and working well
the only thing not working is no A/c condensor fan and it getting hot. compressor getting hot and tubes leading to the expansion valve are hot.

Any ideas??? is the control unit the the thingy in the dash ??

thanks

creaturecat · 07-27-2013, 08:24 AM

i believe there is a fail safe mode, when the condenser fan is inoperative.
A used fan can be inexpensive, 45 minutes to replace.

dporsche74 · 07-27-2013, 08:42 AM

The fan works in high mode if i jump the relay like in the book

would the control unit do that safe mode??

ToreB · 07-27-2013, 12:05 PM

This looks like a CCU fault or maybe a wiring problem/short in the condenser fan circuits. I've never seen this cycling behaviour, fans, servos and all.
The condenser fan shall not cycle but run constantly on low speed when A/C is switched on. Is it cycling on high speed? If so, you have a problem with the low speed circuit/resistor.
It's easy to test the high/low speed, have a look here for details.
As far as I know, there's a fail safe mode in the CCU that will be tripped when there's a problem with the rear fan, so this might not be your problem.
Maybe somehow +12V might be connected to the R14 relay output in the CCU, causing hiccups in the microprosessor inside.
Cheers,
Tore

dporsche74 · 07-28-2013, 10:39 AM

OK tested low speed
A/C fan side is working High and low speeds
but I found that the oil cooler ballast is cracked and not working in low speed mode when jumped on R04 ,, High speed is working

I will order new oil side ballast and install with both R04 and R14 relays and see if that fixes it next..

thanks!!

dporsche74 · 07-31-2013, 12:25 PM

OK installed the new ballast for the oil side and A/c side
and it now works high and low with jumper wires

but STILL when i plug in the R14 relay it is clicking on and off... The A/C fan jumps to High speed and the inside blower is cycling on and off ...NO heat or A/C with the R14 pluged in .. With r14 removed .. everything fully works correctly .. very weird indeed.

anyway to reset the control unit or get a new one?? any ideas?? thanks!!!

ToreB · 07-31-2013, 11:38 PM

This is strange behaviour yes.
The CCU is reset at ignition off, a replacement will have a huge cost. However, most, if not all CCU's are repairable.
I'll dig into the schematics ASAP and try to think of a solution for your problem.
Cheers,
Tore

dporsche74 · 08-01-2013, 06:05 AM

Ok thank you . It looks like it has been replaced beofre with the double A/c button type CCU
Prob just find another used one for a good deal ...

ToreB · 08-01-2013, 12:07 PM

Ah, that explains it!
You have a 993 type Climate Control Unit. The car wiring harness in your car have to be adapted to this type of CCU in order to make it work properly. There's several things to be changed, for starters pin K11, this is the condenser high speed circuit in your car harness. Your CCU uses this output for controlling the rear vacuum shift valve.
This is the reason for your CCU going nuts, I would recommend to stop using the car immediately and disconnect pin K11 from the CCU harness connector to avoid any damage to the CCU.
There's several other modifications to do as well in order to make the ventilation system to work properly in your car, about four or five wire mods. You might consider changing back to a 964 type CCU or have a specialist to do a proper 993 CCU installation.
I have a 964 CCU lying around and could consider an exchange.
All the best,
Tore

dporsche74 · 08-01-2013, 01:14 PM

Oh thanks for the info . Here are pictures of what i have and the back side connectors
When i pulled on it the face fell right off basically.
I dont know if the jumper wire is hooked up correctly or not.. can you tell?
I would like to just install a 964 factory one.
I see a service tag on the back from 2006 two year return

thanks for your help Tore.

dporsche74 · 08-01-2013, 01:16 PM

Pictures

ToreB · 08-01-2013, 11:17 PM

By jumper wire I assume you mean the modification to add the turbo rear fan feedback signal to avoid shutdown of the rear fan. This is only one of the needed modifications. It is difficult to tell if this is done by judging your pictures, I doubt it it is.
Cheers,
Tore

dporsche74 · 08-02-2013, 05:33 AM

Yes the jumper wire from Adrian 964 book . seems to be missing that one.
do you have a good working 964 CCU ..i would take it from you .
thanks