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AC Compressor Help (I'm stuck) - '97 960

Help, Advice, Owners' Discussion and DIY Tutorials on all Volvo's "mid era" rear wheel drive Volvos.

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wasaabi
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wasaabi

AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Tue Jun 11, 2019 7:29 pm

Recently I felt the air warm up as I approached my driveway. I tried my usual (about once every year or so) topping off the 134a from a can. Didn't work so I got deeper into it. Now I am stuck.

First I focused on the compressor clutch. I bypassed the low pressure switch by the receiver/dryer with a paperclip. No go. Then I jumped the compressor with 12v from the battery to the wire directly on the compressor. I heard the magnets engage and I confirmed that with the engine running the compressor spins without obvious restriction. Smooth as silk.

Realizing I had no idea how much refrigerant was in the system, I went out and got a manifold gauge and vacuum pump. I evacuated the system to -30 for about an hour. Initially some vapor came out which I assume is boiled off moisture. I then shut everything down and tested if it could hold -30 vacuum for 30 mins. It did.

I then went to begin refilling, using a scale, with the goal of putting in 900 grams of R134a as per label. First, I added some PEG 150 oil with UV die. Since I did not remove the compressor or open the system, I added a very small amount, probably less than an ounce. Then I started with the first can of R134a. Once pressure equalized, nothing further came out of the can. As I understand it, I need to start the engine at this point so that compressor could pull in more R134a. But starting the engine didn't help because the compressor was still not coming on.

Here's where it gets interesting... So now I was looking for an easier way to jump the compressor. I looked at the relay box under the hood and found that there is 5A AC Compressor Relay fuse (which has continuity) and an AC Relay. I removed it and tried jumping pin 30 to pin 87 to get power to the compressor clutch. No dice. So then I tried jumping with a long wire from the battery directly to pin 87. This engaged the clutch.

Now, with the engine running and the compressor spinning, R134a started flowing in. I was watching it go for a couple of minutes, with the weight of the can dropping, when I noticed smoke from my battery-to-relay jumping wire. This was a stranded wire, maybe 16 gauge. So perhaps it was too thin. I yanked the wire, which shut the compressor and stopped any more R134a from coming out of the can.

So now I was thinking maybe I will do a shorter jump with a thicker cable. I already know I can't jump from pin 30 to pin 87 of the AC relay (because pin 30 is not energized for some reason, perhaps another part of the circuit before this step). So I decided to grab 12v from the horn relay. Unfortunately, this immediately blew the 15A horn fuse.

That seems odd. First the smoking wire and now the >15A draw (blowing the fuse) from horn relay power source only to energize the compressor clutch? Does the AC compressor clutch take that much juice? Or is this a sign of electric clutch failure, and perhaps the cause of the issue?

So now I am about 75% into the first can of R134a, with what appears to be a working compressor clutch, and a working compressor (when jumped) since it is not binding and it sucks in refrigerant when it spins. The relay is good. The low pressure switch is bypassed.

Any ideas? Is the high current draw for the compressor clutch normal? Should I look somewhere else? I am not experienced with ACs but I am pretty good at following directions and logical problem solving.

I appreciate any advice from the experts here.

EDIT: Just checked specs for Sanden compressor http://www.sanden.com/productlibrary/ma ... _Rev_2.pdf. It uses 49 watts. At 12v this is 4.083 amps. This would explain the 5A AC Compressor fuse that Volvo used. This also seems to indicate a problem with my current draw of >15A for the clutch. Only thing that doesn't make sense is why the 5A fuse of the AC Compressor Relay is *not* blown. Not sure if I am barking up the wrong tree. I welcome any insight!


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

wasaabi
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wasaabi

Re: AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Wed Jun 12, 2019 8:58 am

I’m going to update my process here. I’ve checked the ECC diagnostic system. I get 1-1-1 which means no detected fault. As a test of the system I covered the solar/sun sensor on the passenger speaker cover and got the faulty sensor code. So ECC appears to at least think it works. My next step is to check voltage at the relay location under hood to see if problem is before this point. I’m also trying to locate the high pressure “pressostat” to try to bypass it. I really don’t know what I’m doing except for figuring it out along the way. So feel free to chime in!


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

wasaabi
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wasaabi

Re: AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Wed Jun 12, 2019 9:25 am

I have the following relay results:
Pin 86 continuous regardless of AC button
Pin 85 continuous with AC OFF, no voltage with AC ON

I understand this to be correct, meaning AC circuit is normally closed

Pin 30 (and 87 of course, because relay is not connected): no voltage with EITHER AC switch position!

OK, so the problem is in the circuit prior to pin 30. The problem would not appear to be the compressor electrics since the relay doesn’t get juice. Now I am more suspect of the pressostat if I can find it...


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

wasaabi
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wasaabi

Re: AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Wed Jun 12, 2019 9:38 am

I’ve located the AC pressostat / high pressure switch. Very easy to unplug via opening in front bumper below grill. Now to figure out what to do with the 3 pins...


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

jimmy57
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Re: AC Compressor Help (I'm stuck) - '97 960

Post by jimmy57 » Wed Jun 12, 2019 11:51 am

The item on condenser is the high pressure sensor, 5v, ground, and signal to ECM of .4 to 4.2V, increases with higher pressure. It would not blow a fuse, the ECM will shut down the 5V supply if shorted.
The pressostat is on the accumulator by firewall on passenger side but it interrupts a compressor request signal for compressor.
I think you have another fuse blown for the 30 feed for relay. I think the 5A is just relay coil supply
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wasaabi



wasaabi
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wasaabi

Re: AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Wed Jun 12, 2019 11:42 pm

Thanks for the help. Before I saw your reply I messed with jumping the three pins in various combinations and got no result other than to cause the check engine light to go on. Sounds as you described the ECM cut off the switch until I will reset it.

On the advice of a friend, I ran 12v directly from battery to compressor to cause clutch to engage and compressor to spin while trying to get the 900 grams of refrigerant in. I got a bit further but still on the first can. The wire I used was heavier gauge (12?) but still it got kind of hot. Then I started to smell an unpleasant smell closer to the compressor. After a few tries the clutch no longer reliably engages with 12v. It’s sporadic. This would seem to point to a clutch coil issue. But it still doesn’t explain the lack of 12v at pin 30 of the relay? I also confirmed that at the low pressure switch I do see 12v depending on AC switch position. So the ECC selector unit would appear to be working based on that. Before replacing the compressor I would like to try to find out why pin 30 does not have juice. But outside of the 5a coil fuse I don’t know where else to look. Could it be a bad compressor coil caused pin 30 to pull too much current and blew some fuse? But where? Any ideas?


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

wasaabi
Posts: 24
Joined: Tue Aug 13, 2013 5:31 pm
Year and Model: ‘08 XC70, ‘97 965
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wasaabi

Re: AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Wed Jun 12, 2019 11:53 pm

I just located and checked the wiring diagram of the relay in question and it points to fuses 11/2 and 11/16 in the engine compartment. Both are 15a. Since my experiment with the horn relay pin as a power source blew that 15a fuse, I will assume I have a blown fuse to the AC relay power due to the compressor clutch coil shorting. I will check tomorrow and update... Hopefully the numbers match the fuse numbers so I don’t have to check each fuse...


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

wasaabi
Posts: 24
Joined: Tue Aug 13, 2013 5:31 pm
Year and Model: ‘08 XC70, ‘97 965
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wasaabi

Re: AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Thu Jun 13, 2019 9:03 am

Ok I have confirmed that the 15a fuse for "AC Clutch" was blown. I guess I just missed that one first time around and assumed that the 5a fuse was the only one. So the hypothesis is that the compressor clutch is shorting out, this drawing high current and blowing the fuse. Next step sounds like compressor replacement, unless someone knows of a way to replace the clutch coil without removing the compressor.


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

dj_v70
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Re: AC Compressor Help (I'm stuck) - '97 960

Post by dj_v70 » Thu Jun 13, 2019 6:28 pm

I can't answer your questions regarding clutch replacement. However, I wrote a post regarding how to bypass 3 wire high pressure switch for 2000 V70. Possibly that would work for you if you still need it. If you search my posts you will quickly find it, else PM me as I don't read the RWD forum very often any more.



wasaabi
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wasaabi

Re: AC Compressor Help (I'm stuck) - '97 960

Post by wasaabi » Sat Jun 15, 2019 10:58 am

Thank you, good for future reference!

Once I saw that the AC Clutch fuse was blown it confirmed that the issue is a clutch coil short. I’m going to replace the compressor next week. I have a local Volvo guy that’s vintage-oriented and he’s going to do it. I will update once complete with any added info for reference purposes.


2008 XC70 167K
1997 965 146K "The 97"
1990 745 GLE 16-Valve manual + electric overdrive (sold 125K)

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