mohamad jamil

I just bought 1991 964. I noticed that the AC is not working and blowing only air, therefore, I dedicated the week to fix the problem. I started with charging the AC at the dealer. The AC worked, was weak for 1 hour, afterward, it started blowing hot air as if the heater was on.

I took the car to a specialist and they indicated that the system needs flushing, so they did that with gas over and over again. They also change the AC value claiming that there was a leak. The AC is working but can not decrease the temperature of the car beyond 24 celsius and becomes very weak during the day. Adding to the challenge, the car infiltrates all of the smell of the engine and the exterior as well.

I took the car to another specialist and they indicated, the condenser needs cleaning and the external airflow control is not working. I will take the car to the specialist tomorrow to try to rectify the problem.
I am afraid that I am trapped in a guessing game and can not seem to find competent specialists that know what they are doing or follow a structured approach to diagnosing the problem.

I live in Dubai and the temperature here has no mercy. Moreover, I want to drive my car every day and not save it for a lovely weather which is a rare coincidence.

Please help

midnight 911

My first step after checking for leaks would be to make sure your AC radiator fan is working (in both low and high speed). It is very likely that your ballast resistor for the AC radiator fan needs replacing. (Think about replacing your oil radiator fan ballast resistor at the same time.)
Spend some time here: https://www.bergvillfx.com

JohnK964

Also check the servos are operating as they should 2 and 4 control the hot air from engine compartment to the cabin.

ToreB

Thanks for the reference midnight 911.
I guess you have a problem with one or more of the air flow control servos. This is a common issue, and is easily checked in minutes. Next is checking all fans for proper operation. All is covered in my DIY check procedure here.
Cheers,
Tore

JohnK964

I was going to suggest Tores site but he beat me to it I am sure the picture I posted came from his site

griffiths

If you are not familiar with the local club already,
Dubai Porsche Club,
I'd reach out to one of the club officers and ask them what shop in your area is familiar with air cooled models. Figure AC work is common in your climate so it just a matter of finding a tech whom is experienced with the 964/993 climate controls.

After you have had the HVAC controls (climate head, servo's, fan's, etc,) checked out, its time to chase down the common refrigerant leaks with this model. A competent repair shop will have both electronic leak detectors and UV dye trace tools.

1) Hoses and pipes. Unlike the early 911, which had nearly 40 feet of non barrier hose, the 964/993 uses quite a bit of aluminum tubing, however this does not mean its plumbing is not prone to leaks. There are two rubber hoses in the engine bay that will fail over time, and some short sections up by the condenser. Each component connection (ie. compressor, RH rear bulkhead, condenser, drier, TEV, evap, etc) o-ring should be replaced and each of these joints sniffed for leaks after charging the system.
2) OEM factory Evaporators in these models are prone to leakage.
3) TEV's on occasion
4) The lower portion of the condenser due to debris trapping moisture.
5) Compressor nose and manifold seals.

Standard protocol is to install a new drier and add refrigerant oil for losses when R&R components.

964-993 AC

nickyv

Do threads dealing with A/C issues on the 993 pertain to the 964 as well? I find a lot of 993 threads intermingled with the 964. My a/c hasn't worked since I bought my 964 and I'd like to try and fix it. One challenge I have is no glossary of terms. Experienced Rennlisters are awesome, but you folks abbreviate way too much!

griffiths

The two models are nearly identical, however there were some changes to the HVAC (heating, ventilation, air conditioning) controls and servo's along the way.

OEM = original equipment manufacturer
OAT = outside air temperature
PSI = pounds per square inch
TEV = thermal expansion valve
RH = right hand
LH = left hand
PITA = pain in the ****
inHG or HG = inches of mercury
UV = ultraviolet
BAR = a metric term for pressure; 14.5038 psi absolute
ABSOLUT = Russian lubricant
HIGH SIDE = between the compressor outlet up to the TEV; or too many Becks.
LOW SIDE = from evaporator outlet to compressor inlet; morning after too many Becks.
EVAP = Evaporator
SOP = standard operating procedure
MTBF = mean time between failures (or divorces)

Ken D

-nick

^ ha ha

Another one to add to the list- the flapper valves above the rear wheels can get sticky. One can stick such that heat exchanger heat doesn't get dumped to the rear wheels, instead it travels up the sill and tries to push passed the closed temperature control servo. Even if the hot air doesn't push it's way in to mix with the a/c air (and it will), the sill gets hot and radiates inside. Also not great for engine cooling.

Easy to check- lift the up, remove two clamps holding each exchanger hose, and work the flapper open/close. It should have almost zero resistance. If it sticks, spray liberally with penetrating oil then lubricating oil.

Alternatively, if you have a leak in the left/right hot air hose leading out of the sill to the hvac box, the flapper valve won't seal off hot heat exchanger air and will heat up the sill.

I think that this mode of transportation for excess heat is often overlooked because it's unique to the 964/993.

nickyv

Thanks Griffiths! You just opened up a whole new world to me! Thanks to you as well Nick.

911URGE

Mohamad - Welcome to 964 ownership and Rennlist.

Agree with previous posts on what to check in your case especially the mixer servos.

My AC never got real cold and never blew much volume of air. I figured thats how 964 AC systems were. My AC compressor blew and had that replaced along with a recharge. My system is still R12. Still not very cold but it worked.

Then the condenser sprung a leak. Replaced that and the drier along with another R12 recharge. System was colder but still not very cold.

Finally my evaporator died and what was found can only be described in a picture posted below



How would the AC system function effectively with all that gunk in there??

My mechanic has never seen something like this in a Calif car. With a new evaporator the system blows quite cold. It was measured at 59F (15C) and the volume of air through the vents is 3x-4x more. We also needed to adjust the mixer flaps and servos to get cold air from all vents.

If your system is just not blowing cold air within spec's then definitely check the condenser and evaporator for blockages like this along with fan operation.