98 s70 strange ac problem... Not gap ect.

Heath720 · Post by **Heath720** » 14 Jun 2014, 14:52

Hey all....pretty solid on ac diagnostics, not great but I get it.... Jumped low preasure switch and compressor kicked on for split second. Checked fuse and it's good. I unplugged male wire before thermal fuse and applied 12v and compressor runs fine, fan doesn't come on with compressor.. Any ideas, thinking one of relays is bad.

Post by **Ozark Lee** » 14 Jun 2014, 17:14

The fan not coming on says the system isn't building enough pressure - as in the charge is too low. The fan is controlled, through the ECU, by the high pressure switch. If the A/C is actually cooling I suppose it could be a bad high side pressure switch but they normally don't fail unless they get the connector broken off of them. The high pressure switch is a double pole switch so if it is bad it could not only cause the fan to not come on but it could also keep the compressor from running at all when things are hooked up normally.

...Lee

Heath720 · Post by **Heath720** » 14 Jun 2014, 17:32

Thanks lee... I jumped the low switch and compressor doesn't start, even with low freon it should start... Only way compressor starts is when I give it 12v at the male connector before the thermal link. I swapped relay on fuse panel and didn't change. Thinking the fan relay might be bad. Nothing else is making sense

Post by **Ozark Lee** » 14 Jun 2014, 17:59

The compressor will run even with the fan relay unplugged. The fan relay responds from an input from the high pressure switch (via the ECU) but it never tells the ECU or the air conditioner whether or not it is actually working. The temp gauge is about the only indicator there.

The fan relay is easy to test. Ground the relay connections that correspond to the yellow and the yellow/white wires - one at a time individually - that go to the center connector on the fan relay. The fan should toggle between High speed and Low speed when the respective wires get grounded.

...Lee

Heath720 · Post by **Heath720** » 14 Jun 2014, 19:59

Ok I will test it in morning. Any ideas if it's good? Kinda lost. Especially since compressor won't run with low pressure jumped.

Post by **Ozark Lee** » 14 Jun 2014, 20:14

Have you checked for battery voltage at the low pressure switch? If you have no voltage there (on either terminal with the AC on) then the problem is either the AC relay or the controller. If you do have voltage there then the problem is towards the compressor.

What are the particulars on the car? Turbo? Auto climate unit or manual? The compressor circuit is different depending on which variant you have.

...Lee

Heath720 · Post by **Heath720** » 14 Jun 2014, 21:58

98 s70 NA, man controls. Light on ac switch comes on. I'll check low preasure voltage and the fan relay. I'm gonna chase this till I fix!!! Thanks a ton for the help Lee

Heath720 · Post by **Heath720** » 16 Jun 2014, 16:22

12.15v at low pressure plug when ac is turned on.... Do I'm assuming control is good.

Post by **Ozark Lee** » 16 Jun 2014, 17:46

Battery voltage at the low pressure switch is a sign that everything in the cabin is OK. I will need to dig through the schematics to see where things go from there on your car. Have you tried to just bypass the thermal fuse?

...Lee

Heath720 · Post by **Heath720** » 16 Jun 2014, 18:12

If I apply 12v to the male/female connector before the thermal.. compressor starts and runs fine. Think I should bypass it just to double check?