1997 960 AC Compressor Fuse Keeps Blowing
1997 960 AC Compressor Fuse Keeps Blowing
1997 960 Wagon: Got my A/C charged, blowing ice cold and working properly. Vents all work great. One of the initial issues was A/C compressor 15A fuse in engine fuse block was blown. Worked fine in driveway and on first test drive, then 2nd time went out in 95-degree heat, A/C working great, after about 4 miles stopped blowing cold and when I checked, fuse was blown again. Is the compressor trying to pull too much of a load? I don't think it's a short anywhere; otherwise, it would blow immediately. Would putting a 20A in its place hurt anything? If it blows too, I'd really suspect something wrong with compressor. I see the fog light system in the same fuse box using the same relay has a 25A fuse. Thanks.
VOLVO: 98 S70 GLT, 97 960 Wagon,
96 850 GLT Wagon, 89 240 DL, 85 244 DL
SAAB: 98 900S Convertible, 97 900S Convertible,
94 900S 5-Door, 92 900 4-Door, 91 900 Turbo Convertible
BMW: 82 320is
TRIUMPH: 80 TR7 Convertible
OLDSMOBILE: 93 & 94 Cutlass Supreme Convertibles
CHRYSLER: 90 New Yorker Fifth Avenue
96 850 GLT Wagon, 89 240 DL, 85 244 DL
SAAB: 98 900S Convertible, 97 900S Convertible,
94 900S 5-Door, 92 900 4-Door, 91 900 Turbo Convertible
BMW: 82 320is
TRIUMPH: 80 TR7 Convertible
OLDSMOBILE: 93 & 94 Cutlass Supreme Convertibles
CHRYSLER: 90 New Yorker Fifth Avenue
-
jimmy57
- Posts: 6694
- Joined: 12 November 2010
- Year and Model: 2004 V70R GT, et al
- Location: Ponder Texas
- Has thanked: 4 times
- Been thanked: 320 times
No, the wire in the circuit determines the fuse limit. If it has a wire that melts at 17 amps then you'll at the least harm other wires in wiring harness and at the worst burn down the car.
Unfortunately the magnetic coil for clutch on compressor can fail and draw too much current.
If an ammeter is used between battery + and whichever side of removed fuse socket goes to compressor you'll get the current draw. Probe both and one will click in compressor and the other won't do anything. If it draws 10 or more amps then its the coil. If it draws 3-5 amps then coil is OK and you have a bare or chafed wire that shorting to body and popping the fuse.
10 A will not blow the fuse but usually a shorted clutch has to be on for a bit and get warmed up before the current draw goes up and blows fuse.
Unfortunately the magnetic coil for clutch on compressor can fail and draw too much current.
If an ammeter is used between battery + and whichever side of removed fuse socket goes to compressor you'll get the current draw. Probe both and one will click in compressor and the other won't do anything. If it draws 10 or more amps then its the coil. If it draws 3-5 amps then coil is OK and you have a bare or chafed wire that shorting to body and popping the fuse.
10 A will not blow the fuse but usually a shorted clutch has to be on for a bit and get warmed up before the current draw goes up and blows fuse.
All the theories are correct but wire size is not all that determines the size of the fuse. Circuit load does and Ohms law now becomes the guide.
At idle, the compressor is moving refrigerant but at a small volume. At road speed, the volume increases. One item to look at is the refrigerant control. One type may be an expansion valve, other types can be an orifice tube. Either way, if there is any debris blocking refrigeration control, current will rise and so will compressor load. The compressor is now working much harder.
Second point is the condenser fan. When A/C is engaged, that fan must be operating or expect higher than normal system pressures.
Have an HVAC certified technician test that system. If you used off the shelf (mechanic in a can) A/C top up or a re-sealing mixture, that HVAC technician needs to know, or the equipment will be seriously damaged and/or the recycled refrigerant will be contaminated.
At idle, the compressor is moving refrigerant but at a small volume. At road speed, the volume increases. One item to look at is the refrigerant control. One type may be an expansion valve, other types can be an orifice tube. Either way, if there is any debris blocking refrigeration control, current will rise and so will compressor load. The compressor is now working much harder.
Second point is the condenser fan. When A/C is engaged, that fan must be operating or expect higher than normal system pressures.
Have an HVAC certified technician test that system. If you used off the shelf (mechanic in a can) A/C top up or a re-sealing mixture, that HVAC technician needs to know, or the equipment will be seriously damaged and/or the recycled refrigerant will be contaminated.
-
jimmy57
- Posts: 6694
- Joined: 12 November 2010
- Year and Model: 2004 V70R GT, et al
- Location: Ponder Texas
- Has thanked: 4 times
- Been thanked: 320 times
You are talking about circuit design. When someone wants to upsize the original fuse then all of what you said is moot. Then the size of the wire is what determines what fuse is tolerated without disaster.
If you know the full details of the circuit then you can make an informed decision about whether a larger fuse is safe. If you do not know the facts of all wires protected by the fuse then to install a higher amperage fuse will have the risk just as I wrote above.
The load on compressor is of no consequence on the clutch magnetic coil circuit. The compressor is not electric motor driven. The coil would actually have increased resistance and reduced current flow if the load on the compressor resulted in heating the magnetic coil due to Ohm's law you mentioned.
Magnetic winding coils like the one in the compressor have fine wire that is varnish coated to act as insulation. That wire is prone to failures where vibration and age cause some motion that abrades the insulation and shorts the winding to some extent. This reduces the resistance in the coil and increases the current flow. In most a/c clutch failures I have ever diagnosed and repaired the fuse would blow jut as the OP has described. When I substitute ammeter for the fuse and monitor the current it will be above normal to begin with but not enough to open fuse. After the coil heats and the contact between worn wires is increased the resistance decreases and current increases and it reaches a level that would open the fuse. If the initial current draw is normal (5 amp range and goes down with coil warming within a minute) then coil can usually be ruled out. In that case the wire having contact with ground becomes a suspect.
Some clutch coils have a capacitor for field collapse spike capture and the cap can fail and short. I don't remember the 960 compressors using a cap like the older Volvo compressors on 740/940/760 4 cylinders.
The radiator fan and blower fan are not loads on the compressor fuse.
If you know the full details of the circuit then you can make an informed decision about whether a larger fuse is safe. If you do not know the facts of all wires protected by the fuse then to install a higher amperage fuse will have the risk just as I wrote above.
The load on compressor is of no consequence on the clutch magnetic coil circuit. The compressor is not electric motor driven. The coil would actually have increased resistance and reduced current flow if the load on the compressor resulted in heating the magnetic coil due to Ohm's law you mentioned.
Magnetic winding coils like the one in the compressor have fine wire that is varnish coated to act as insulation. That wire is prone to failures where vibration and age cause some motion that abrades the insulation and shorts the winding to some extent. This reduces the resistance in the coil and increases the current flow. In most a/c clutch failures I have ever diagnosed and repaired the fuse would blow jut as the OP has described. When I substitute ammeter for the fuse and monitor the current it will be above normal to begin with but not enough to open fuse. After the coil heats and the contact between worn wires is increased the resistance decreases and current increases and it reaches a level that would open the fuse. If the initial current draw is normal (5 amp range and goes down with coil warming within a minute) then coil can usually be ruled out. In that case the wire having contact with ground becomes a suspect.
Some clutch coils have a capacitor for field collapse spike capture and the cap can fail and short. I don't remember the 960 compressors using a cap like the older Volvo compressors on 740/940/760 4 cylinders.
The radiator fan and blower fan are not loads on the compressor fuse.
-
- Similar Topics
- Replies
- Views
- Last post