Air Cooled Toys

Hi guys,

I'm trying to track down a problem in my A/C system. The symptom is that the A/C blower fan will only come on a high speed and is cutting in and out. I have done the obvious things, which include changing/upgrading to the new style ballast resistors for both front fans, a new resistor for the rear fan, installing a brand new relay in position R14 and a brand new CCU fan in the dash.

I have checked all of the fuses and jumped the R14 relay and everything seems to be testing as it should. The power tests out at ~12 and 4 volts, continuity is ~1.2. When I jump the relay, I can get the AC blower fan to run on slow or fast speed.

The couple of background details that may be relevant are:
1. The A/C was not blowing cold when I bought the car in October. I had the mechanic charge the system after the PPI the day I bought the car. The A/C system started working, but a couple of days later it was 100+ degrees and on a road trip, the A/C freaked out and blew HOT AS HELL air that I could not stop. It seemed to act normally the next day and has not had that behavior since.

2. My first weekend of ownership, I changed the pollen filters among other things and managed to turn a simple DIY into a hellish nightmare. I accidentally popped the cap off of the 14-pin wiring connector on the passenger side instead of splitting the connector at the interface of the pins and all the wires came spilling out of the connector. I thought that I put them back correctly, but now I fear not. I believe that this connector is referred to as number X69 on sheet 16 for Model 95/2 of Volume VII: Wiring Diagrams of the Factory Repair Manual. Unfortunately, I only have the freebie scanned/PFD version of the manual from the Internet and the page is too fuzzy for me to read the colors of the wires in the diagram. I believe that the problem could be that at least one pair of wires in the connector is now wrong. I could really use a clear copy of that page.

2. After the pollen filter/electrical connector fiasco, I took the car to another shop that had a Porsche scan tool, and was told that the ballast resistors were shot. I replaced them as stated above. When I was replacing the A/C blower fan resistor, I ran into a mouse nest in the area behind the fender liner in the vicinity of the resistor. I looked at the wires and did not note any damage. Could my problem be the wiring at the fan, since everything checks out at the relay? I'm ready to remove the fender liner and dive back in with my multimeter.

Thanks for you help.

Todd

x50type

No wire colours are shown on the the sheet you refer to.

It only mentions that the 14 pin connector x69 is in the luggage compartment right - which you already know.

If you give me the wiring sheet reference i will find the colours for you.

Air Cooled Toys

Thanks so much. You are right. What I really need a good copy of is the detail on X69, which is shown on Sheet 3 for Model 95/2 of Volume VII: Wiring Diagrams of the Factory Repair Manual.

I really appreciate the help.

Todd

ToreB

I would start with checking the condenser fan signal from the CCU to the relay. Is Terminal 85C at R14 grounded when you press either of the A/C buttons? Does the relay activate when A/C is on?
If OK, there is a problem with the wiring from the relay to the fan, most probably due to mouse damage.

If you are getting hot air while A/C is on, (and the temp **** is not turned way up) you might have a problem with the fresh air intake servo and/or the mixer servos. The mixers can stop in the open position, allowing hot air from the engine to overshadow any cool/cooled outside air.
Cheers,
Tore

x50type

OK -- here's the X69 connector with colours.

Let me know if you can't see what you need.

Thanks

IXLR8

...

Air Cooled Toys

Thanks guys.

Todd

Air Cooled Toys

Hi Tore,

Thanks for the advice. I did not get continuity when I grounded terminal 85c of R14 when I pushed the Max A/C button. However, I did get continuity to ground on terminal 85c before and after I turned on the ignition. As soon as I turned on the ignition, I no longer had continuity. The A/C button did not change the continuity reading if the ignition was on.

I felt R14 clicking in conjunction with the fan kicking on and off at high speed once R14 was reinstalled and the car was started with the Max A/C button pressed. Cold air was coming out and the A/C fan in the fender was kicking on and off every several seconds. I felt R14 click each time the fan cycled on and off.

Does this indicate a CCU problem or the wiring from the relay to the fan.

I appreciate your advice.

Thanks again,

Todd

ToreB

The test should definitely be done with igntion on, the CCU will not activate the condenser fan without power. I would think it's more likely you have a problem elswere in the car than in the CCU itself. By your description, the CCU output is working, and it's activating the relay as is should, but not in the correct way, if you understand what i mean.

To sum up, you need to find out why the CCU is using condenser fan high speed only, and why it's pulsing on and off. It might have something to do with the Three-level pressure switch. A pressure above 17.5 bar will switch to high speed on the fan. On early 993 '95 models the CCU is also involved in turning on the high speed. Your initial post indicate that you have the late 95 model, thus no connection from the CCU to condenser fan high speed. (pressure switch activation only)
The switch can be checked with an ohmmeter, details are given on my HVAC DIY pages: www.porschehvac.bergvill.com
An OBD diagnosis on the CCU would clarify things as well, fault codes could be read out.
Cheers,
Tore

Lorenfb

"I'm trying to track down a problem in my A/C system. The symptom is that the A/C blower fan will only come on a high speed and is cutting in and out."

The 993 CCU requires three power (#30, #15, X). Anyone of the three being
intermittent will cause your problem. If there's a any problem in the engine
compartment with the rear fan, it can become problematic for the front fan.

Read here under 'Porsche - CCU 964/993' for more info:
http://www.systemsc.com/problems.htm

ToreB

Todd, which fan in your is cutting in and out? My understanding is that it is condenser blower. This fan is placed in the left front fender.
The two interior blowers are placed in the firewall air box, beneath the windscreen, and will indeed, as Lorenfb states, have problems if there are any issues in the rear fan assembly.
Cheers
Tore

Air Cooled Toys

Hello again Tore,

I wanted to clarify one item from your previous post. I am not sure if my 993 is an early or late 1995 model. I referenced sheet 3 for Model 95/2, because that was the page of factory workshop where I found the diagram for connector X69. My car's production date was 4/94. The VIN ends in 321107 if that helps.

Yes, you are correct. The problem is with the condenser blower fan that is in the left front fender. I believe that the interior fans are working properly.

I have not had time yet to test the three-level pressure switch as you suggested in an earlier reply, but I will hopefully have some time and energy after work one day this week.

After reading everything I can find online and that has been sent to me, I am thinking that the issue is likely one or a combination of the following:

1. The system is overcharged/overpressured (over 17.5 bars) This assumes that the mechanic that recharged the coolant put in too much.

2. The wire is compromised (mouse damage) from the ballast resistor to condenser blower fan.

3. The three-level pressure switch is bad.

4. The wiring got jumbled in connector X69 when I put it back together.

5. The rear fan relay is faulty.

I will test items 2 through 5 over the next few days. I will have to have a mechanic test the pressure in the A/C system if necessary.

Do the above items all seem like possible culprits? If so, what order should I test them in?

Thanks again.

Todd

ToreB

I would think it's unlikely that there something wrong with the fan wiring as long as the manual test at R14 is OK.
A fault in the rear fan would only affect the interior blowers, and not the condenser fan.
Measuring the three-way pressure switch with an ohmmeter would be cheaper than having a tech checking the A/C refrigerant level.
You could also use a Porsche compatible OBD tool and read out any fault codes from the CCU. That would help things a bit.
Good luck in your endeavours Todd. Keep us updated on the result.
Cheers,
Tore

Air Cooled Toys

Hi again Tore and A/C gang, I'm back with more info.

I checked the three-way pressure switch for continuity with a multimeter and it it seemed to behave as is should.

Next, I bought an A/C manifold gauge set from Harbor Freight Tools and measured my pressure. It seems like my refrigerant level may be a tiny bit high, but I wanted to get some opinions.

My test conditions were 68 degrees F/20 degrees C. I warmed up the car with a spirited 20 minute drive with the A/C off. I then set up the manifold gauge set and measured ~ 75 PSI/5.171 Bars on both high and low sides as a static measurement. Then, I ran the A/C on high (big snowflake button pressed) for 10 minutes and had a buddy hold the throttle at 2,000 RPMs while I measured the pressure on the gauge set. My readings were 210 PSI/14.48 Bars on the high side and 10 PSI/0.69 Bars on the low side. My center vent temperature was ~37.4 F/3 degrees C - 42.8 F /3 - 6 degrees C. When the compressor kicked in the readings were a little different. At idle, they were 190 PSI/13.1 Bar on the high side and 24 PSI/1.65 Bar on the low side.

It appears from BS911's write up on the A/C system that my pressure is about 36 PIS/2.48 Bars too high on the high side at 68 degrees F/20 degrees C.

Could this account for my condenser fan running only intermittently on high speed with no low speed function (remember, I already replaced the ballast resistor and the relay)...

As always,

Thanks,

Todd

ToreB

I can't comment on the pressures or how to measure these other that the three-level pressure switch will turn on high condenser fan if the pressure exceeds 17,5 bar. My DIY page describes how to measure this at the switch.
Cheers,
Tore