AC Compressor only engages when Low pressure switch is jumped Topic is solved

LOB · Post by **LOB** » 02 Jun 2021, 05:42

Summer has hit Scandinavia!!! I've got enough refrigerant in the system (45 PSI at 26 c) and the airflow is really cool while being jumped an no blinking light from the ECC panel!
Where do I go from here? I've read that there might be a faulty switch on the compressor itself that can cause this fault and that this switch is somewhat redundant and can be jumped permanently. What else can be wrong? The AC-relay? Where is it located? I've also read that you could determine what's wrong by measuring the electricity in the low pressure switch. I've got 13 volt on one of the pins (with ground on the other pin or bare metal in the engine comp.). I've read that you should have + 13 volt on both pins but that doesn't make any sense to me albeit I'm not an electrician. Can the temperature sensors malfunction? Any advice is appreciated!

dj_v70 · Post by **dj_v70** » 02 Jun 2021, 16:13

2 terminal switch?
PSI reading is with ac off or on?

Disconnect cable from switch and put your jumper on cable harness.

Read ohms across switch with ac off.
Read ohms across switch with ac running.

If you have a pressure gauge, also record pressure on low side port with ac both off again while on.

Report back.

LOB · Post by **LOB** » 03 Jun 2021, 01:42

Thanks a lot! Its appreciated,
47 PSI with AC on at 77 Fahrenheit (I started this with adding some butan/propan mixture into the system so maybe its slightly overfilled!?)
130-150 ? PSI AC off (120 is of the scale of the gauge)
1 ohm (100% resistance) on the switch both with the AC on and off, having the harness for the switch jumped.

Post by **abscate** » 03 Jun 2021, 04:12

That is too high on the low side for straight R134A , but I don’t know how a R134A and propane mix measures up. I think I would evacuate and charge by mass

Remember static pressure measurements don’t mean much

LOB · Post by **LOB** » 03 Jun 2021, 04:37

At 26 c or 77 F I've read that the pressure should be 40-50 PSI. Can you interpret this chart?
https://www.duracool.com/chart.html
"Dew" and "bubble" ?

Post by **Chuck W** » 03 Jun 2021, 05:56

Have you not tried to replace the LP switch?

( I see no mention of doing so)

LOB · Post by **LOB** » 03 Jun 2021, 06:30

Chuck W wrote: ↑03 Jun 2021, 05:56 Have you not tried to replace the LP switch?

( I see no mention of doing so)

No, can that be done without re-filling the refrigerant?

Post by **Chuck W** » 03 Jun 2021, 07:51

LOB wrote: ↑03 Jun 2021, 06:30
No, can that be done without re-filling the refrigerant?

Yes. There is a valve under the sensor that closes when the switch is removed.

dj_v70 · Post by **dj_v70** » 03 Jun 2021, 16:53

I don't see any need to replace switch, 1 ohm is the correct answer. Pressure is not low either. This should work, I am confused. Try again?

LOB · Post by **LOB** » 03 Jun 2021, 23:36

What do you think of this suggestion from another post;

"Anyhow, he pointed out that the Volvo has multiple safety relays, and it would be quite safe to bypass this relay.

It is simple, just locate the male and female relay wires at the compressor, unplug them, leave the relay in the compressor out, connect the incoming male and female.

(The problem can be checked by a more technical person by applying 12 volts to the output of the firewall mounted ac relay. If the compressor clicks on, it is the internal relay in the compressor. This was how he confirmed the issue)

Initially it did not function. By a miracle of luck, I thought perhaps there was a need to clear some computer decision, so I removed battery power and reset the system."

viewtopic.php?t=29275

But I haven't seen any firewall mounted relay. But there's a relay behind the glovebox?