Mads

Hi

a few weeks ago i went to a local shop to fill my AC. Because i wasen't working.
The shop only put 600g on the system, and i stopped working a few days later. Last week i went back to the shop, and they did a test on the system, it held vacuum at 10 bar, no coolant lost. They filled the system with 860G R134a..

But the system i still not working, the shop did not have time to troubleshoot, but they said i could be the refrigerant pressure switch.
I have read "THE 928 HVAC SYSTEM Basic Operation and Troubleshooting" But i need a bit more guidance
Can i bypass the switch to see if it's the problem ?

Mads

WallyP

Start at the connector for the AC clutch, on a black wire, located near the oil dipstick tube. If you don't have battery voltage there (ignition on, HVAC set for AC), then go back along that wire as outlined in the guide until you find battery voltage.

A common problem is the small relay inside the HVAC head unit.

Make sure that the blower works - poor fuse connection, faulty relay are common problems here.

Alan

You could briefly bypass the switch and see if that allows the compressor to run - however that doesn't tell you the switch is bad only that it isn't conducting - perhaps it doesn't see the correct pressure for some other reason? You could change the switch out or just test the pressure there.

Do not just run without the pressure switch - it is there for a reason - to protect the compressor.

Alan

Mads

ok, so i can test the clutch, if i put the 2 connectors on the switch together?
Can i change the switch without recharging the coolant ?

Mads

alabbasi

You should take it to another shop. THey're not giving you enough information to diagnose the problem. Some system leaks will show up under pressure that will not show up under vacuum. They should at least try to put a sniffer on the system to see if they can make identify the location of the leak.

dr bob

Mads, what year is your car? R134a cars have a more sophisticated pressure switch that protects against both too-low and too-high condenser pressure. So too much refrigerant might also cause your symptom.

The Most Common problem besides loss of refrigerant is failure of the compressor clutch relay in the control head. The diagnostic procedure in your guide will tell you if this is our failure.

Mads

it's a '89 so it's delivered with R12, and converted around 2002.. i will take a picture of the switch.. But i don't have time to diagnose this weekend

Mads

Mads

I have testet the clutch, and it works fine, the compressor runs when i bypass the power.. But still no cold air is's that normal? and does that brig me closer to the problem?

Mads

StratfordShark

If no cooling with compressor running (make certain it's engaging when clutch powered - you may just be seeing the pulley rotate), then suggests a major leak in system and also suggests the shop didn't do things right when they checked system held vacuum ok

Mads

the compressor is running, and there is R134 in the system, no leaks according the nitrogen test.
coud it be one of the switches on the drier?

Mads

StratfordShark

Mads the switches control fans and cut off compressor if pressu too low. If you are running compssor from separate power source and still no cooling then the switches are not an issue.

Cooling with compressor running is down to having refrigerant and compression/expansion. Maybe problem with expansion valve? At this point I am out of my depth as I am comfortable only with tracing electrical prolems with the AC.

Alan

Why do you say this? the switch on the dryer IS the refrigerant pressure switch, and there is only one physical switch not 'switches' (though it does have several internal switch elements).

What were you testing before? - when you concluded it wasn't working...

If you power the clutch directly and the compressor is rotating and you don't get cool air - it could be many things - BUT the most logical in this scenario - given the recent history - is that a lot of refrigerant has leaked out, that explains no cooling & why the refrigerant pressure switch isn't conducting.

Go to a different shop and get the leak located & fixed

Alan

Mads

Sorry if i was unclear.. i was talking about the clutch, it works, and it the compressor turns around when i put 12V to the clutch wire.
The shop told me that the system was holding pressure, when they did the nitrogen test. and they also said that there was 860G r134 in the system. They also put some tracing fluid in the system... is there a way i can detect the leak myself ?

Mads

SteveG

We are very good at instilling paranoia that mechanics aren't competent when we don't have details, doesn't mean your shop is bad. They should have put a sticker on that says there is dye in the system. Yes, you should be able to detect the dye (if it is leaking) if you know what it is. Autozone may have the same dye, etc. If you are going to do that, I would also buy gauges for 134 and find out what pressures you have with the system running. There are many threads here with this very problem. "Search" is your friend, otherwise, you already have knowlegable people watching this thread.

There is a problem with just adding and then adding some more 134 -- unless they started at zero you don't know how much 134 is in there now nor how much oil.

You do know that just b/c the pulley is turning does not mean the clutch is engaged. You should be able to hear it click when sys is switched on.

Mads

The shop is one of the best regardig AC in the area.. But they at only 2 in the shop, and one of them is on vacation so they don't have time to look at my car right now..
Regarding the clutch, it clicks, and i can se that after the click that the center turns around.
But as i said it only clicks when i put 12v directly to the black wire.

Mads