S90 a/c woes

ernie143 · Post by **ernie143** » 16 May 2012, 12:53

My '98 S90's a/c after running for approximately 40 minutes at a designated temperature starts blowing back hot air as a result of the compressor stopping. If I wait awhile and restart the a/c it will blow cold air. However, if I max out the temperature to 64 degrees it blows cold air without any interuption. Could it be a switch or a sensor that's mal-functioning?

Second issue is under load (acceleration) the a/c will almost cease working until I level off with the accelerator pedal. Is this "normal".

TIA,
Ernie

Post by **billofdurham** » 16 May 2012, 13:45

Welcome to Matthew's Volvo Site.

I'll deal with issue two first - yes it is normal on the 960/S90. It is to ensure that the A/C does not rob the engine of power when it is needed. A/C uses some 7-12 bhp when the compressor is driven.

The S90 A/C system has a self diagnostic capability. A fault in the system is indicated by the AC OFF button flashing. Does this happen on yours?

Bill.

Post by **jimmy57** » 16 May 2012, 16:58

Those cars can suffer from the clutch gap issue. Running it on full blast with the automatically selected high fan can work the system hard enough so that it does not cycle compressor and give the clutch its opportunity to fail to engage. In Phoenix with 90'd daytime temps the compressor won't cycle too much anyway.
You can verify this but be careful. You run it until it stops in the settings where it has been failing. When it stops leave engine running w/o touching controls. Use a wooden broom handle and at # o'clock on the compressor clutch plate, approx 3/4 inch in from the belt pulley edge on the front of the car face, tap the clutch plate. If it clicks in and start operating and resumes cooling then the clutch wear has created a large enough gap for the magnet winding to not be strong enough to pull it in.
When clutch wiring cools the magnet gets a bit stronger and it is able to pull that plate in again until it gets hot.

ernie143 · Post by **ernie143** » 20 May 2012, 17:24

Bill & Jimmy,

Thanks! I'll check and get back to both of you.

Also, approx 2 years ago I had my system charged as the system was doing the exact same things described. So, last weekend I bought a DIY a/c can of Freon 134a with a gauge and emptied a 20 oz can into the system. However, it's the same; nothing has changed.

Should I have my system evacuated (maybe air inside) and recharged? Could it be that this is the culprit?

TIA,
Ernie
1998 S90
1966 1800S

Post by **jimmy57** » 20 May 2012, 18:06

The a/c loss of dash vent airflow is going to be a leaking diaphragm unit. Either floor/defrost diaphragm or the recirculate diaphragm. These two on that car are suction to extend instead of suction to retract. Extend type have a seal on the rod that extends and the vacuum is sealed by that seal. When the seal cracks then it leaks and when accelerating the source of vacuum, the intake manifold, no longer has vacuum and the door allowing air to the vents closes and it diverts to defrost outlets.