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Saab
A.C. diagnosis
This article mainly pertains to the classic Saab 900 1984- up (cars with Lh 2.4.2 fuel system are different) air conditioning systems, but I will have some hints and tips for other Saab models as well. I've received many letters on Saab AC diagnosis so I have decided to do a write up- being that we are closing in on summer. So it's the first hot day of the season and you hit the old snow flake on the dash and nothing happens, no clicking of the compressor ,no stumble of the engine as it adjusts to the extra load, and most especially no cold air...
The first thing to check is your fuses, for classic Saab 900 check #25,#9 and #6 on Saab 9000 check #20,#7,#4,#6 (check the wiring diagram for your car to be sure. All pins # and fuse # are typical to that model, but can be different than stated. If you have a blown fuse and it blows again when you replace it, check the Radiator fans and the comp. These components have been known to burn out and cause blown fuses.
The second thing to check is if you have any freon.(R12) or (R134). This can be done by jumper wiring your low pressure switch on the receiver dryer located in the passenger side fender. If your ac compressor now kicks in with the low pressure switch jumped, and the switch on the dash depressed, best chances are you're out of freon due to a leak. The most common leak on the 900 is the dual hose on the back of the compressor.While your compressor is running you also can check the sight glass atop the receiver dryer. If you see a stream of bubbles this indicates low freon. Watch out, a completely empty system will show no bubbles but you may see some streaking oil.
If your compressor does not kick on you have an electrical problem in front of you. You can easily do most of your diagnosis from the relay socket and the switch plug. I have provided a chart below from Saab that shows what readings you should get on cars with an ac time delay relay1986-. You will need a volt ohm meter and the wiring diagram for your Saab model and year.
Start by putting a jumper across pin 30 & 87b of the relay(center pin some are labeled 87a) this connects 12v to the compressor through the over heat switch on upper radiator hose (component 168) via fuse 25. If the compressor does not come on check component 168.
If your compressor does come on, run the following relay checks and trace the circuit that comes up with faulty results. If all looks good you may have a bad relay or switch depending on what your testing.
This is a great way to determine where the fault lies by only unplugging a relay and running a few tests. Be sure to get the correct diagram for your car, without it you can go crazy chasing false results. Early 80's models are similar but don't use the time delay portion on their relay.
Time delay is a function that won't allow the A/C to kick in until 10 seconds after the car is started. This is done by a signal to pin 50 on the relay. This is a 12v signal the same circuit that triggers your starter motor. With out this signal the A/C will never kick in.
pin 15) +12v in run and crank on ign switch from positive buss bar under relay panel fed by ign. switch.
pin50) +12v during crank from the ignition switch.
pin86) +12v from pin 8 of the ac switch in dash (when depressed) through the ac low pressure cut off switch and the ac anti frost switch.
pin30) +12v at all times via fuse #25
pin87) To pin 85a on the cooling fan relay
pin87b)or pin87a) To the ac compressor
pin31) Ground through the negative terminal under relay panel
pinTK) no continuity with ground except at full throttle(this cuts out ac at full throttle.
pin16) signal to Lh control unit 16v only(this is to kick up the idle speed with the Idle air control valve).
Position H on 900 fuse/ relay panel
Saab A/C switch check
pin4) +12v
pin5) ground for switch illumination
pin7) +12v from fuse #6 when ign. in run position.
pin8) To pin 86 A/C relay
Anti frost switch: Located below right hand side of dash behind glove box area.
Function: Turn off ac compressor if evaporator temperture falls below 35 degrees f.
Check: should
have continuity across the 2 spade connectors at above 35 to 45 degrees.
Component #171 in wiring diagram
A/C high temp cut out switch: Located in upper radiator hose
Function: Cut out A/C compressor when engine coolant reaches above 240F.
Check: You
should have continuity across terminals at normal engine temp.
component #168 in wiring diagram
A/C low pressure cut out switch: Location on top of receiver dryer in right fender under horn.
Function: This will cut out A/C any time the pressure drops below 40 psi. Due to a leak and low freon level or outside temperature below 45 degrees F.
Check: With proper
charge and temp. above 50 degrees should have continuity across switch.
component #166 in wiring diagram
Throttle switch: Located on throttle housing.
Function: reduce engine load by cutting out A/C at full throttle.
Check: There
should be continuity across terminal 2 and 3 at full throttle, and no
continuity at closed throttle.
component#203 in wiring diagram
(This article is meant to educate a consumer,or as a guideline for professionals. You can cause serious damage to your vehicle and/or cause yourself injury. Only those qualified should attempt repairs. I do my best to assure that the above info is correct but take no responsibility for any damages incurred.)
Feel free to e-mail with any tech questions