c900 A/C problem - belt always running and A/C not working

Saabstudent · Mar 21, 2006

Okay those who frequent the workshop forum will know that i have been trying to sort out a rad cooling fan problem (engine fan not cutting in) and that i am near a fix (new thermoswitch).

However, while i have been mucking around in the engine bay i have obviously knocked something and created another problem

Doh!

As my car has A/C it has two fans on the rad - one that is linked to the A/C and the other standard one for the engine cooling. So at the weekend i noticed that the belt attached to the A/C compressor (see photo) was always running when the engine was on even if the A/C was not activated.

At this time time the A/C fan on the rad does not run. When switching the A/C on in the cabin the light comes on behind the button but the nothing changes at the compressor and the Fan still does not come on at the rad.

I can't really test if the A/C is working as it is very cold out there anyway, and i have checked fuse No.6 for the A/C and it seems ok. Also when i remove the fuse the A/C compressor belt continues to run - is this correct?

Help appreciated folks - one of the things i was so proud about on my T16s was that both the cruise (which has also recently started working intermittently) and A/C work(ed) perfectly.

Photo below shows the offending belt (circled and arrowed so there is no confusion

Thanks as usual guys,

G

900t · Mar 21, 2006

The fan only goes on when the A/C compressor engages. You can tell this when the clutch "centre" piece of the shaft starts turning. The belt and pulley always turn when engine is turning.

The compressor won't engage if it is too cold or if there is no refrigerant in the system. I think the temperature cut off is around 3 C.

Saabstudent · Mar 21, 2006

Hmmmmmm, surely it has been warmer than that recently? Could it really be such a simple fix?

Heres hoping.

So that would mean neither the fan or clutch would engage at temps lower than this?

G

s900snt · Mar 21, 2006

YES, the belt always turns when the engine is on.

If the A/C is actually on, you will hear a loud distinct "CLICK" when you push AC button with the car running and the hood open with you outside the car. If it's working...and you have a muffler on your car...YOU WILL HEAR THE CLICK.

If your A/C is not working, the most likely cause is the low pressure sensor.

TO TEST IF THIS IS THE CASE:
go to the front right fender (engine exhaust side) and look for the reciever/dryer. It's a black canister smaller than a soda can with a small clear 'looking glass' on the top. There will also be a sensor threaded into it with two leads.

Turn the car on, turn the AC on, then short the two leads to the reciever/dryer.

If you hear the click when you short the leads, your system is low on pressure and needs to be recharged before it works.

Only leave the wires shorted for a few seconds, running the system with it low on freon pressure can damage the compressor if done for more than a few minutes.

The temprature sensor mentioned above has nothing to do with ambient temprature and is only designed to cycle the AC so it doesn't freeze over with continuous use. Pay no attention to it.

Austin

rawill · Nov 25, 2019

s900snt said:
YES, the belt always turns when the engine is on.

If the A/C is actually on, you will hear a loud distinct "CLICK" when you push AC button with the car running and the hood open with you outside the car. If it's working...and you have a muffler on your car...YOU WILL HEAR THE CLICK.

If your A/C is not working, the most likely cause is the low pressure sensor.

TO TEST IF THIS IS THE CASE:
go to the front right fender (engine exhaust side) and look for the reciever/dryer. It's a black canister smaller than a soda can with a small clear 'looking glass' on the top. There will also be a sensor threaded into it with two leads.

Turn the car on, turn the AC on, then short the two leads to the reciever/dryer.

If you hear the click when you short the leads, your system is low on pressure and needs to be recharged before it works.

Only leave the wires shorted for a few seconds, running the system with it low on freon pressure can damage the compressor if done for more than a few minutes.

The temprature sensor mentioned above has nothing to do with ambient temprature and is only designed to cycle the AC so it doesn't freeze over with continuous use. Pay no attention to it.

Austin

An old post, but very helpful.

Thank you, did the "short test" with the drier wires, instantly the compressor clicked in.

So low gas.
That should be an easy fix, will book it in for a re gas today.

Saabstudent · Mar 21, 2006

So its almost def low on gas then?

Damn, must have a leak somewhere.

G

s900snt · Mar 21, 2006

That's the most likely cause of the AC not coming on.

Do the test though, and we'll see for sure.

It can also be a super slow leak that needs no repair. Sometimes the system is just under the minimum pressure, and not completely empty.

I'm curious to see if it kicks in when you bypass the pressure sensor.

Also, If you're uncomfortable doing that with the engine running, you can do it with the ignition and and the engine off. Doing it that way will ASSURE that nothing can possibly be damaged.

You will still hear the click

s900snt · Mar 21, 2006

tade

BTW, you should be happy!
I'd trade working A/C for a turbo motor any day.
;oops:

Jim Mesthene · Mar 22, 2006

s900snt said:
Also, If you're uncomfortable doing that with the engine running, you can do it with the ignition and and the engine off.

If your A/C relay is the time-delay type, it will only engage 10 seconds after the relay sees 12 volts at the #50 terminal on the relay from the starter. Without the starter signal, the A/C will never engage. If your A/C relay doesn't have a #50 terminal, it is not the time delay type.

vstevens · Jul 23, 2009

Jim,

where do you find this #50 terminal? is there a way to jump it to check the compressor clutch? I've already jumped the terminals on the receiver/dryer and no click heard from compressor.

woywitka · Mar 22, 2006

s900snt said:
The temprature sensor mentioned above has nothing to do with ambient temprature and is only designed to cycle the AC so it doesn't freeze over with continuous use. Pay no attention to it.

Austin

my A/C will not turn on when the temp reaches zero, my A/C didn't work for a few weeks when the temp was down. but we had a 17C day on sunday and the A/C clicked on again and ran the car nice and cool

.

unkleG'sif · Mar 22, 2006

i think that leaks usually occur where the pipes connect to the a/c rad - down behind the bumper on the right hand side - the alloy connectors on the end of the pipes corrode with the steel from the a/c rad:evil:

mine had a leak that was so slow, the a/c dude could not even accurately find it, even with his superduper gas detector thing (makes the wierdest noises

)

i just jibbed off the a/c when i had the engine out - i would never have used it anyway - its a bit of an uneccessary in the UK if you ask me - but thats just my 2 1/100ths of a pound

G

William A Yelton · Mar 22, 2006

Seems a common ailment. Mine has not worked well since my 94 900 turbo was NEW

Saabstudent · Mar 22, 2006

Ok,
All working today.

Went out to try the test as described by s900snt and found the wires in a plastic shroud/case. As i had no tools to hand at the time i removed the wires from the connectors, gave em a good blow and re-connected them. Started car and started the A/C and it was all working :cheesy:

Now my only diagnosis is that either there was a faulty/loose conenction and my removal/re-insertion of the wires cured this or it really was too cold for the system to work (it was actually quite sunny this aft). Another forum suggested that it may be the ambient temp that was too blame. I also did the check as suggested by the Bentley to look through the inspection window on the reciever/drier and it was all clear - suggesting that the system is fine.

Fingers crossed that it continues to work, but from now on i will keep my beady eye on it more often!

Thanks everyone,

G

900t · Mar 22, 2006

William A Yelton said:
Seems a common ailment. Mine has not worked well since my 94 900 turbo was NEW

In Sveeden the air be cold enough :lol:

See there is a good side to the GM / Saab deal, Saab has access to GM's stunningly powerful air conditioning systems

cdaly · Mar 22, 2006

Saabstudent said:
look through the inspection window on the reciever/drier and it was all clear - suggesting that the system is fine.

This check is only relevant when the system is running. When you start up the AC, you should see bubbles rushing through the receiver window for a short while until, when the system stabilises, the bubbles should dissappear and the window should be clear. This tells you the system is fully charged. If the bubbles persist or if the liquid does not reach the window, the system is low on gas.

Matthew · Apr 5, 2006

Our local LSUK (Lucas) shop advertise free air-conditioning checkups. if you have an LSUK branch local, then you could make use of that free service.

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c900 A/C problem - belt always running and A/C not working

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