1998 Volvo S70 AC compressor not turning on.

[pb49415]

So another observation I noticed and want to pass on is that I rechecked the voltage at the terminals under the relay. Terminals 3 and 5 have 12v across. 1 and 2 are transient under 12. 1 of the two (1&2) has 6 something and the other is millivolts. My thoughts are that one of these two terminals under 12v is a switched from the dash button (s)? But, there is no change in voltage when dash button is turned on/off. I also rechecked the relay for continuity across all posts. 3 and 5 are cycled by the open/close of the relay and 1 and 2 do nothing at all. Not sure what this information means since I don’t exactly know how this system is set up. Any thoughts?

[dj_v70]

I am going through the exact same issues now on my 2000 v70. Every thread in the past that I found didn't resolve it either. Symptoms are the same, here are some of the test steps:
a) jump relay 22/2 pins 3 and 5. Compressor starts right up, that is good. The relay could be bad, or the computer is not engaging it.
Possibilites that I can think of:
1) The relay is bad. I heard that you can swap relay with horn relay, but I haven't looked any further into that yet. I am going to look into this next.
2) Computer is not allowing relay to get engaged. This is the hardest path. I have vida/dice which should help me troubleshoot, but I don't know how to use it:( And, it is not applicable to your car. Reasons why the computer might not be engaging relay:
Climate Control Unit isn't telling computer to engage it (inside temperature or ac power control). Should be able to check at pins to computer
but I don't have schematics yet. Vida is supposed to have them but I don't see them in my software:(
Freon low pressure switch. This is by the firewall on my car. It should read <1ohm on a meter. That passes for my car.
Should check this at wiring to computer, haven't tried that myself yet though.
Freon high pressure switch. This is the linear 3 prong switch that you mentioned earlier. I haven't seen any way to troubleshoot this yet,

[dj_v70]

Found another post with link to wiring diagrams:
http://www.volvowiringdiagrams.com/volv ... rtible.pdf
See page 44 for Electronic climate control diagram.

With this, I'll revise my last post:
a) We already proved that compressor works by jumping ac relay. Need to determine whether relay is bad or computer refused to engage it.
b) Jumper pin 2 of relay to ground with relay in place and see if compressor is on. Need to get creative here. Maybe try to wrap 30 gauge wire around relay #2 pin close to relay case and connect other side of wire to a 30ohm resistor and then to ground. Then put relay back in socket. Start car and see if compressor is on. If so, relay is good and computer (ECM) is refusing to engage relay. If not, replace relay.
c) Check all ECM inputs:
1) I don't know how to test line pressure switch outputs. It would be real nice if someone would measure resistance between these 3 terminals of pressure switch with car off:) Then we could make a dummy resistor network for test purposes.
2) CCM output. It looks like voltage should vary at pin 1 of low pressure switch when AC is engaged inside of car. If not, CCM or interior sensors are likely broken.
3) As I mentioned in last post, verify that low pressure switch has <1ohms. Else the switch is broken or, duh, there is not enough freon.
4) There appears to be an input from instrument panel. Not sure what this is about though or how to check it yet:(
5) ECM gets power from ignition switch and main relay. My first thought is that these are likely fine.
6) Check associated wiring with ohm meter and if all are fine it might be ECM.

[Matty Moo]

Paul gets on MVS instead of texting Matt, who owned the car previously. Lol

[pb49415]

I checked ohms on low pressure sensor while installed. It actually registered 0 and had continuity across it. Not sure, maybe if it was uninstalled it may register differently. So, I got my buddies spare relay and that didn’t get the compressor going either. As far as interior sensors that were mentioned previously. I have no clue where they would be or how they function. I do know the compressor works when relay is manually tripped. That is fact. I guess I’ll just have to go without AC since I doubt I have any other resources. Unless someone has another idea????

[abscate]

I think you have traced fault to where you arent getting a command signal to the relay from the ECC control unit (ECC is an abbreviation for Electronic Climate Control, but is often used to refer to the control unit in the dash)

I guess trying a junkyard ECC control unit might be next?

[pb49415]

Yeah, that’s my thought too. The ECC Unit is the dash control above the stereo right? Or is it further inside the dash? I’ll see if my buddy has one he can send me.
Thanks

[scot850]

The ECC unit is the unit above the radio. Remove the radio and then push up slightly on the rear of the unit it should pop out fairly easily, although if it has never been out they can be stubborn.

While in there it is worth removing the cabin temp sensor. People never clean those and after 20 years they gum up with airborne crap and the little fan that pulls the air past the temp sensor stops turning. It sits behind a small louvre/grille to the left of the ECC unit which is where it draws the cabin air from. Wear long sleeves to remove it as the edges of the ECC unit hole are sharp and will likely give you a nice graze on your forearms.

To remove it requires disconnecting the wire connector at the back of it and then feeling for 2 small bumps on the sides of the unit at 180 degrees apart that have to be depressed to release it. Be careful not to loose the rubber seal that fits to the front of the part as it usually sticks in the hole it sits in and worst case will drop behind the dash. It needs to be fitted for the sensor to sit correctly.

It can help to remove the button to the left of the louvre/grille to help access to remove the sensor.

Neil.

[pb49415]

Yeah I know the location you’re speaking of. Would that in itself cause the compressor not to turn on? Is it possible to remove it and jump across the terminals to get connectivity?

[dj_v70]

I believe the following is true, but not 100% positive:
Check for 12v on one side at low pressure switch. With interior ac switch on, you should have 12v and off should be 0v. If you get that, your issue is not car interior electronics.