Diagnosing A/C system, How do I test/bypass high pressure switch?
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    1. #1
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      Diagnosing A/C system, How do I test/bypass high pressure switch?

      A/c system currently has no refridgerant in it. The system has a leak which is most likely the evaporator, but will put dye in and check for leaks before tearing everything apart. There is another issue however, jumping the low pressure cut off switch by the firewall should allow the compressor to run as if there is refridgerant in it, but it's not running when I jump the switch, leading me to believe that there is another issue. I checked the compressor and clutch, relays and fuses, and the ECC module, all are working properly. When I pull the connector off of the high pressure switch(located between the ECU box and rad support) then put it back on, the compressor kicks in for about 5 seconds and then shuts off, but doesn't kick on every time. I'm thinking that the HP switch is bad. There are three wires out of the connector, numbered 1,2,3. Does anyone know which pins to jump to temporarily bypass? Or how to test the HP switch?

      Vehicle is 2000 V70R
      Last edited by sjmcarz; 05-27-2013 at 06:16 PM.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    2. #2
      Member burnout8488's Avatar
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      I have *never* heard of a failed HP switch, but that's not to say it isn't impossible. I think the issue may be that there is absolutely zero refrigerant in the system.

      Wish I could help, no clue what the pins do or why it's a 3 pin instead of a 2 pin like the LP switch.

      Want me to drop a spare HP switch in the mail for testing purposes if you can't figure it out? Pretty sure I have one laying around. (Known working)
      '99 S70 AWD - 15G - ARD Green
      '97 854 Manual - GF's car
      '13 VW CC Sport 6MT

    3. #3
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      Quote Originally Posted by burnout8488 View Post
      I have *never* heard of a failed HP switch, but that's not to say it isn't impossible. I think the issue may be that there is absolutely zero refrigerant in the system.

      Wish I could help, no clue what the pins do or why it's a 3 pin instead of a 2 pin like the LP switch.

      Want me to drop a spare HP switch in the mail for testing purposes if you can't figure it out? Pretty sure I have one laying around. (Known working)
      Thanks, I may take you up on that if i can't figure how to temporarily bypass it. I do have the schematic for the system, and all three wires go into the ECU so I don't want to just start jumping wires for fear of burning up something. I may just take the switch off and try to figure out how it works.

      Edit: Actually, I'll check the switch pins first to see if there's continuity between any 2 of the three pins.
      Last edited by sjmcarz; 05-27-2013 at 09:24 PM.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    4. #4
      Junior Member b2fkb0's Avatar
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      I'm in the same boat as you! I tried to jumper the low pressure cutoff switch with the same result (nothing, compressor clutch won't lock in). I found my two leaks, repaired them and added new refrigerant. The compressor began to cycle on/off and seemed to be in business. Next day I went to run it and had the same result. I bought a gauge set yesterday so I'll see what that shows me. Possibly the same evaporator issue (hopefully not!) as I haven't checked that yet...
      94 854 na turquoise, 98 v70r black, 98 v70xc olive, 99s70t5m black
      93 245 silver sold,98V70R silver sold, 98v70xc sandstone sold, 96 855r black totaled, 96 855r white sold,

    5. #5
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      Quote Originally Posted by b2fkb0 View Post
      I'm in the same boat as you! I tried to jumper the low pressure cutoff switch with the same result (nothing, compressor clutch won't lock in). I found my two leaks, repaired them and added new refrigerant. The compressor began to cycle on/off and seemed to be in business. Next day I went to run it and had the same result. I bought a gauge set yesterday so I'll see what that shows me. Possibly the same evaporator issue (hopefully not!) as I haven't checked that yet...

      Could very well be your evap. I did put refridgerant in mine at one point and still no compressor kick in, so besides my leak, there is something else going on.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    6. #6
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      Checked the HP switch with an ohm meter today with no refridgerant in the system and the connector off. Here are the readings between the pins on the switch:
      Pin 1-2 = 1120 ohms
      Pin 2-3 = open
      Pin 1-3 = open
      None are grounded.

      I also checked the HP switch in my daughters 2000 S70 with a working, charged A/C system:
      Pin 1-2 = 14,600 ohms
      Pin 2-3 = 12,200 ohms
      Pin 1-3 = 8,500 ohms.
      None are grounded.

      Interesting that this switch is not designed just for on/off. I was surprised to see these ohm values, unless they were caused by corrosion in the switch.

      Burnout8488, do you have an ohm meter? If so, would it be possible for you to check the readings on the extra HP switch that you have? It would be much appreciated if you could do this for me!
      Last edited by sjmcarz; 05-28-2013 at 09:23 PM.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    7. #7
      Member burnout8488's Avatar
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      Sure!

      Switch off the car:

      1-2: 17.7 ohms
      2-3: 17.7 ohms
      1-3: 23.5 ohms

      On my '99 S70 properly charged (by weight) with no leaks:

      1-2: 50.4 ohms
      2-3: open
      1-3: open

      Is there a chance one of us is using the wrong scale? (tens hundreds thousands?) It's odd though that the switch on your car mimics the open circuits that the switch on my car's *charged* system does. Maybe your switch is stuck in a high pressure state despite not being charged? But your daughter's car doesn't show any opens, which is confusing since mine does on the same car.
      Last edited by burnout8488; 05-28-2013 at 11:50 PM.
      '99 S70 AWD - 15G - ARD Green
      '97 854 Manual - GF's car
      '13 VW CC Sport 6MT

    8. #8
      why dont you just check the voltage? it should be 1V per 100 psi so about 1v with system off approx.
      i have had plenty of those fail.
      there is a bulletin about them from volvo.

    9. #9
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      Great! Thank you for taking the time to do this! I havn't used my ohm meter for a while but the symbol on the meter reads K- ohms, so if I put the switch on the "20", I'm assuming it will read up to 20,000 ohms, am I correct? I used this scale on my daughters car, and had readings of 14.6, 12.2, and 8.5, so 14,600, 12,200, 8,500 ? For the 2000 Vr, I used a 2000 ohm scale, which came out the same as direct @ 1,120. ohms. I'm more interested in your charged system showing similar readings as far as what's open as my non charged system. Maybe I'll check the HP switch in my wifes 2001 XC, although it is a P2, not P80. Still would like to figure out which wires in the connector to jump, although if the system uses resistance values, jumping the connector may not work.
      Last edited by sjmcarz; 05-29-2013 at 09:05 AM.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    10. #10
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      Quote Originally Posted by garbergtsi View Post
      why dont you just check the voltage? it should be 1V per 100 psi so about 1v with system off approx.
      i have had plenty of those fail.
      there is a bulletin about them from volvo.
      Thanks. Where would I check the voltage? And how about if there is no pressure in the system?
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    11. #11
      jumping the connector wont work but i have done it with a old TPS and got it to work

      if there is no pressure it will be close to 0V. the P2 sensor is the same as well

    12. #12
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      Quote Originally Posted by garbergtsi View Post
      jumping the connector wont work but i have done it with a old TPS and got it to work

      if there is no pressure it will be close to 0V. the P2 sensor is the same as well
      So I keep the connector plugged in, and check for voltage on which wire? Car/ignition on?
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    13. #13
      Member burnout8488's Avatar
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      For testing, you can always just borrow the switches off of your daughter's or wife's cars. There is a Schrader valve underneath them so the system won't discharge if you remove the switch.

      No idea on the ohm readings, I wasn't able to get a proper reading unless I used the "20" on my multimeter, which scales everything down so the number is actually readable. When I used the "2000," I just got abbreviated numbers since the scale was too high for the application. I think the resistances (at least on my meter and HP switch) are simply 17, not 1700. But yeah, the voltages will tell a different story. I'm no electrician though.
      '99 S70 AWD - 15G - ARD Green
      '97 854 Manual - GF's car
      '13 VW CC Sport 6MT

    14. #14
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      I found out that the HP switch is actually a sensor, hence the ohm readings and not just on/off. I'm going to try a few things first before revisiting the HP sensor, one being am I getting voltage at the LP switch. Also, I didn't realize that the system would stay sealed if I removed the sensors, that's good to know.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    15. #15
      so there are 3 wires, it works just like a TPS or any other sensor that alters resistance.... one wire has 5V, one wire is ground and the third is your signal. signal is 1v per 100 PSI of high side pressure.
      just take a DVOM and check the 3 wires....

    16. #16
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      Quote Originally Posted by garbergtsi View Post
      so there are 3 wires, it works just like a TPS or any other sensor that alters resistance.... one wire has 5V, one wire is ground and the third is your signal. signal is 1v per 100 PSI of high side pressure.
      just take a DVOM and check the 3 wires....
      Thanks, looked at the schematic and can see which wire is which.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    17. #17
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      Update, tested voltage going into and out of the sensors, all seems fine. Replaced the evap today and all is well, COLD air! It seems that the R-134 was leaking out so fast, that the sensors would not allow the compressor to kick on, even if I tried putting refridgerant in. I did need to jump the low pressure switch to help suck refridgerant in quicker after I replaced the evap.
      2001 V70 XC, Black/Beige, 48,000 miles, Wifes wheels
      2000 S70 ASR N/A Silver/Graphite, 194,000 miles, Daughters wheels, Rear spoiler, Xemodex
      2000 V70R, Emerald(Olive) Green/Graphite, 120,000 miles, Sons wheels, Father and son project car, 2002 2.4T, 19T, Greens, Delco TCV, Snaab intake pipe, VDO boost gauge
      My wheels: Changes almost daily but usually a Volvo of some sort

    18. #18
      Member burnout8488's Avatar
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      Awesome! Perfect result.
      '99 S70 AWD - 15G - ARD Green
      '97 854 Manual - GF's car
      '13 VW CC Sport 6MT