9two8

In the last couple of months I had a new compressor and drier fitted, when I got the car back the aircon was working great, in the past few days I,ve noticed it,s blowing coolish or slightly warm.
Looking in the site glass on the drier it,s crystal clear ( air-con running ) I,m feeling a bit frustrated really as this has cost a lot to fix.
I rang the shop that does my work, and they say to bring it in, it probably needs re-gassing ? what do you think ?

Any information I can give to the shop would be good.

Ken
80 928 S
5 Speed

UK

fraggle

You've got a leak somewhere. Find it first.

blown 87

Or the heater valve is not fully closing.
Usually when they start loosing cooling, but still cools some what your sight glass will not be clear.
If clear it means it is full or very low.

9two8

.., thank,s I also thought about the pesky heater valve, although it,s less than two years since I fitted a new one, ( says nothing really I suppose) ?

Ken
80 928 S
5 Speed

UK

9two8

....., just this minute checked my history folder, could,nt believe it when I saw the Heater valve was last renewed in June 06 !!!

SeanR

I'd start by checking to see if it is getting proper vacuum. Is it closing all the way? Do you have a vac leak while driving and it is opening?

TheoJ

hi
Here's a link with some extra info: http://jenniskens.livedsl.nl/Technic...4/MyTip431.htm The valve is also available at a local Mercedes parts supplier at tiny cost compared to Porsche. You might also replace the small hose that connects the valve to the engine. They tend to get brittle.
Diagnosing: watch the valve arm get pulled in by vacuum when you start the engine and heat is off. If it does, the cabin side of the valve should stay cold (more or less). If you still get heat there or typically have a heat spot on the left lower side of the center vent in the console, you have a leaking valve. It happens.
If it doesn't close, you might have a big vacuum leak, or a faulty membrane in the heater valve actuator. Had that myself a month ago...

dr bob

Back to the AC...


Easiest way to tell if the sight-glass is full-clear vs empty-clear is to have someone switch on the AC while you are watching the glass. Engine running of course. Button push will start the compressor, and in just a few seconds you should see a wave of bubbles then liquid in the glass. If you don't see that, it's quite likely you are low on refrigerant.

Refrigerant escapes through leaky hose and line connections to components, damaged components like the condenser, and from the compressor shaft seal. There are other places like the compressor manifold plate seals, expansion valve seals, and the pass-through bulkhead fittings where the rear aircon lines come through the floor under the passenger seat. Everything but the compressor shaft seal should be bubble-tight, no leakage. The shaft seal is an oil-lubricated mechanical seal the needs a film of oil maintained to keep it sealed. The AC must be operated periodically, even in winter, to maintain that oil film. Else it will leak.


Your AC folks will know how they like to check for leaks. I use an electronic detector. Others like the dye in the oil and search for traces later with a good blacklight. Sniffer allows me to check without diassembling to see the dye traces. Plus if the engine bay is less than perfectly clean, oil traces will be lost in the mess. Sniffer gives me instant results too, with a minimum charge present.


Find the leak, fix the leak, replace the drier if the system is opened, evacuate, and recharge.

outbackgeorgia

Heater valve default with vacuum leak or no vacuum to the valve is hot water ON, so vacuum leak or failed valve diaphragm is not good.
Clear sight glass means charged fully (usually see a few bubbles go by with R12) or empty. If so, agree with Fraggle to find the leak.

9two8

Many thank,s to all who posted very helpful .., It still seems odd that last time the car was used ( one week ago ) the aircon was practically blowing ice cubes, and useing it today hardly any real cold air. Seems like these valves are really temperamental ( if it is the valve ?)
In Theo,s post there,s a mention of a heater valve for Merc/ VW/Audi, part number A0008305784.., has anyone tried this alternative, and are they better made then OE Porsche ?
A cursory glance at the pipework in the suggested areas etc, does,nt seem to show any tell-tale leakage, and having a detailed engine bay also helps in showing any leaks etc.
Would it help to close the valve ( temporarilly ) with a tie-wrap, in order to see if it is at fault or not ? as previously mentioned it,s six years since I fitted a new valve, maybe it,s time for a new one irrespective ?


Ken
80 928 S
5 Speed

UK

Bill Ball

Is the compressor clutch engaging? If the charge were so low that there were no bubbles, the low pressure switch would block the signal to the compressor clutch. If it's engaging, then you have a fair charge. Maybe not enough to be chilly, but you have enough charge that there should be bubbles in the sight glass.

Re: The heater valve. The heater valve may be OK but not closing. There are at least two possible causes for that - no vacuum due to a leak in the vacuum feed or a leak in another of the climate control actuators which will "steal" vacuum from the heater valve. So, you need to check that all the lines from the climate control vacuum solenoid gang that is behind the radio and fix or block off any that do not hold vacuum. The other possible cause is a failed mixing motor. If the mixing motor is broken in the "warm/hot" position, the heater valve will not be sent a vacuum signal by the electrical solenoid as the solenoid signal for the heater valve is processed by the mixing motor electronics. What you see in this case is that the heater valve will close when the climate control system is switched OFF and the motor is running, supplying vacuum, but as soon as the climate control is put to any on position, the heater valve opens in response to the mixing motor being stuck in the warm position. The mixing motor is on the driver side of the heater core box in the cabin, visible from under the dash. As you move the temp slider between the hot and cold ends, you should see the cam and arm on the mixing motor move. If it does not move, it's broken.

Also, the heater valve may close appropriately but have an internal leak, although I have only seen that be a minimal leak past the valve, raising the air temp maybe 10F over ambient with the AC off. Anyway, if when cruising with just vent air, no AC, if the vent air is warmer than ambient after the system has had time to equilibrate, then you have a partial heater valve leak. If the valve didn't work at all (wide open), the vent air would be VERY, VERY hot with the AC off.

9two8

Many thank,s Bill for your advice, does this advice apply to a 1980 4.7 Right hand drive application OB ? Or are there variations ?

I,ll be able to check out the compressor engagement when I take the car back to the shop next week and I,m not on my own, ie, ideally one person to switch air-con , and one to view and listen for the click of the clutch engagement ?

Ken
80 928 S
5 Speed

UK

WallyP

You can check for clutch engagement on your own. With engine running and A/C on, look at the front of the compressor using a torch. If the center is turning with the belt, the clutch is engaging.

While you are checking that, feel of the lines at the condensor (the small radiator in front of the radiator). If the refrigeration system is working, the lines will be hot or at least very very warm. The larger line at the back of the engine compartment should be cold. If the lines are hot and cold, the refrigeration system is working to some extent.

9two8

..., thank,s I,ll check out your advice and report back what I, and the shop discover.

Ken
80 928 S
5 Speed

UK

dprantl

If the clutch is spinning, you can check to see if the A/C system is cooling by comparing the temperature of the high and low side pipes. The high side (thinner pipe) should be warm/hot and the low side (thicker pipe) should be ice cold after a minute or so the system is running. An easy place to do this is where the pipes go through the firewall, or take the plastic cover off the aquarium by the firewall and feel the pipes before they go into the expansion valve. This will work on any refrigerant system, even the one in your fridge or house.

Dan
'91 928GT S/C 475hp/460lb.ft