2000 v70: Troubleshoot AC high pressure switch

[dj_v70]

No question for the group here, just figured I'd document how I am troubleshooting my 2000 V70 AC that was totally dead. Some of this I found in other places, but couldn't find it in one place. I think the way that I eliminated the AC linear pressure switch might be unique.

Here is link to 98-2000 AC wiring diagrams:
http://www.volvowiringdiagrams.com/volv ... rtible.pdf
See page 44 for Electronic climate control diagram.

a) Hook up AC pressure gauge to low side. Verify pressure is at least 25psi.
b) Remove AC relay and short pins 3 to 5. If compressor clutch starts spinning, this proves compressor and wiring is minimally functional. In my case it was. If it wasn't need to check AC fuse and wiring to compressor.
c) In my case, I was able to use VIDA/DICE to engage AC relay, compressor started spinning. That proves relay is good also. If I didn't have VIDA/DICE, I would take relay out of car, put 12V between pins 1 and 2 on relay and verify resistance between pins 3 and 5 goes to 0ohms. Also, verify that pin 1 in relay socket has 12V (from main relay).
d) If all checks out good so far, the ECM is not engaging the AC relay (by pulling relay pin 2 to ground). In my case I know the ECM output is good because VIDA/DICE was able to engage it. Without VIDA/DICE, assume ECM is good until all other possibilities are discarded. If I didn't have VIDA/DICE, I could have used an ohm meter to verify connectivity between ECM pin and relay pin. Other more likely possibilities:
e) CCM output. Disconnect low pressure switch at firewall. Verify that pin 1 of connector receives 12V when AC is turned on inside of the car and goes to 0V when turned off. If not, need to troubleshoot AC electronics inside of car. My CCM test passed.
f) Verify that low pressure switch resistance is <1ohms. Else the switch is broken or, duh, there is not enough freon.
g) There appears to be an temperature input from instrument panel. Not sure about this input to ECM, I never got to this.
h) ECM gets power from ignition switch and main relay. My first thought is that these are likely fine. If everything else checks out, try this last as well as verifying continuity between all sensor wiring before considering replacing ECM.
i) Linear pressure switch. This is the high pressure (HP) cut-off switch. I put this last, but in reality, I checked this after low pressure switch. I was able to test mine with VIDA/DICE. It read 0V, 0kpa. Of course, it could be either the switch itself or wiring or ECM itself. I took 2 500ohm resistors and put them in series. I connected one end of the resistors to end socket on HP switch connector and one end of the other resistor to the socket on the other end of the HP switch connector. I twisted the other 2 resistor leads together and stuck them in middle socket. I turned AC switch on inside car and compressor clutch engaged. VIDA/DICE reads 2.5V and 1500kpa for my fake pressure switch. I am off to junk yard tomorrow to get another HP switch. Without VIDA/DICE, the HP switch can be tested by putting 5V across outer pins of pressure switch and using volt meter to read output of middle pin. It should be at least 1V (I think that is 25psi), and (much) less than 2.5V (215PSI) with AC off.

[scot850]

Many thanks for taking the time to detail your test process.

Matthew/abscate, is this one to add to the repair file?

Neil.

[Orchid70]

Thanks - the link is not complete.

[pmondrian]

Hi,

This is a nice write-up. I need to test the high-pressure switch for my 2011 S40 a/c as I can't get the clutch to turn on and it's either the high-pressure switch or the ECM, I think, as everything else checks out. How did you know to use 2 500amp resistors for the test and do you know how I would determine this for the 2011 S40 high pressure switch?

Thanks,
Tom

[dj_v70]

I used 500ohm resistors. In my case I had access to VIDA/DICE and was able to experimentally look at pressure on VIDA while trying different combinations. I'd highly recommend buying VIDA/DICE off of eBay or similar if you are doing any Volvo troubleshooting.

[abscate]

Part number for the 1994-2000 high pressure switch is 30767231

If some has the pressure vs resistance table for this lets post it up here

Undocumented speculation. I believe this switch works as a resistance bridge with a 5 volt supply from the ECU being divided by the variable resistance (controlled by pressure) being fed back to the ECU.

From this diagram it looks like pin 3 gets the 5V reference, pin 2 shuttles the voltage dependent on pressure back to the ECU, and pin 1 is the ground voltage ( probably internal ground to the ECU, NOT chassis ground.

Tom, your 2011 uses a different part then this which we will document , too.