IPD sale XeMODeX - Experts in Volvo Electronics

Get email notification of topic replies. Log in or register (free). Amazon Link Buy anything with this and it helps MVS!

Wanting create a repair procedure for 850 blower control.

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

Jonesy
Posts: 16
Joined: Sat Oct 13, 2007 6:47 pm
Year and Model:
Location:

Wanting create a repair procedure for 850 blower control.

Post by Jonesy »

My 850 has developed the common "Interior fan only blows on high setting" issue. I have looked around the web, some folks say that it is a resistor pack problem, others say that it is a transistor module failure, and that the transistor is an MJ802, which costs about $3.50 at my local parts store.

I am an electronics service tech, so I would like to find out once and for all:

Which part commonly fails, and if this part or parts can be re-furbished rather than paying high prices for Volvo parts, for example replacing a transistor or resistor rather than buying an expensive new module.

I would like to put together a step by step procedure for this repair to post here, but before I go in pulling my dash apart tracing wires, I would like to ask if any forum members have previous experience with this problem, and give me any clues on the location of the modules or resistor pack so that I can remove and dis-assemble them to se if they can be re-furbed.
Ozark Lee
MVS Moderator
Posts: 14798
Joined: Thu Sep 07, 2006 8:24 am
Year and Model: Many Volvos
Location: USA Midwest
Has thanked: 4 times
Been thanked: 56 times

Post by Ozark Lee »

Both assertions are correct but it depends on what kind of climate control unit you have.

The electronic climate control uses a MosFET transistor to control the fan speed. The manual climate control uses a resistor pack of series resistors to control the speed.

The way to tell which type for unit you have is to look at the temperature markings. If the temperature is marked with a series of graduated width bars then it is a manual unit. If it is marked with actual degree temperatures then it is an electronic unit. The manual unit also has fan speed settings ranging from 0 to 4, the electronic unit ranges from AUT to a picture of a fan blade.

I have heard that the resistor packs can fail due to a thermal fuse but I have never tried to repair one. When mine failed it was fairly obvious that one of the wirewound resistor wires had burned up.

A writeup on repairing the power stage for an electronic unit is here:

http://www.brickboard.com/AWD/index.htm?id=1202115

To the best of my knowledge no one has come up with a direct replacement that doesn't involve soldering extender wires on the leads. The original transistor is no longer available.

...Lee
'94 850 N/A 5 speed
'96 Platinum Edition Turbo
Previous:
1999 V70XC - Nautic Blue - Totaled while parked.
1999 V70XC - RIP - Wrecked Parts Car.
1998 S70 T5
1996 850 N/A
1989 740 GLT
1986 740 GLT
1972 142 Grand Luxe
Jonesy
Posts: 16
Joined: Sat Oct 13, 2007 6:47 pm
Year and Model:
Location:

Post by Jonesy »

Thanks for the great reply Lee, can you describe where the resistor pack is or how to get to it?

There are 2 plug-in modules near the blower assembly, one blue and one black. The black one has a circuit diagram on the case, showing a FET and a bipolar transistor. I was considering disassembling it and testing the transistors with my Peak analyzer, can't see anything that looks like a resistor pack though...

The link you posted is very helpful, but doesn't describe the part's locations.
Ozark Lee
MVS Moderator
Posts: 14798
Joined: Thu Sep 07, 2006 8:24 am
Year and Model: Many Volvos
Location: USA Midwest
Has thanked: 4 times
Been thanked: 56 times

Post by Ozark Lee »

The ECC power stage should have two connectors going to it. The manual unit only has one connector.

The wire colors going to the electronic unit are:

Yellow/Brown, Violet/White, Gray/ Red, and Red on Connector A.

The wire colors on Connector B are Black and Blue.

From what you describe you have an electronic unit.

The manual unit's resistor pack only has one connector and its wire colors are Green, Red, White, Yellow/Violet, and Black.

Disconnect the connectors from the unit and remove it from the air duct. The manual unit has a wirewound resistor, usually coated in green, with several taps on it. The electronic unit has a big aluminum heat sink.

If you repair the electronic unit please take some pictures along the way and post them back, it will be a huge asset to the Volvo Community. Paying over $120.00 for a Mosfet transistor is insane.

...Lee
'94 850 N/A 5 speed
'96 Platinum Edition Turbo
Previous:
1999 V70XC - Nautic Blue - Totaled while parked.
1999 V70XC - RIP - Wrecked Parts Car.
1998 S70 T5
1996 850 N/A
1989 740 GLT
1986 740 GLT
1972 142 Grand Luxe
Jonesy
Posts: 16
Joined: Sat Oct 13, 2007 6:47 pm
Year and Model:
Location:

Post by Jonesy »

"If you repair the electronic unit please take some pictures along the way and post them back, it will be a huge asset to the Volvo Community. Paying over $120.00 for a Mosfet transistor is insane."


I agree, no-one should pay that much for a transistor. I will gladly take a series of photos if I need to rebuild the power unit, I guess my confusion lies with the location of the unit itself. From reading the various posts I should be looking for a large heat sink, I assume it is actually inside the air duct? I can't see anything outside the unit except the black cubic plug-in module that I mentioned, it has a FET inside according to the diagram on it, but it clearly has no heat sink, so I guess this isn't it.

Making the electronic repair will be easy, if I can find the module in the first place. I have several FET's here that should match the original Sony device. I will try finding it using the wire color codes that you have kindly supplied.
Ozark Lee
MVS Moderator
Posts: 14798
Joined: Thu Sep 07, 2006 8:24 am
Year and Model: Many Volvos
Location: USA Midwest
Has thanked: 4 times
Been thanked: 56 times

Post by Ozark Lee »

The module is inset into the air duct so you will not be able to see the heat sink unless it is removed - they use the air from the cabin blower to cool the module. On the blower resistor that I had to replaced on my manual unit the assembly was held in with a single T-25 torx head screw and it was kind of a prick to get to due to a wiring harness in front of it. I used a T-20 torx at an angle to carefully remove the screw.

I think the ECC power stage is the same but I have never actually seen one.

...Lee
'94 850 N/A 5 speed
'96 Platinum Edition Turbo
Previous:
1999 V70XC - Nautic Blue - Totaled while parked.
1999 V70XC - RIP - Wrecked Parts Car.
1998 S70 T5
1996 850 N/A
1989 740 GLT
1986 740 GLT
1972 142 Grand Luxe
Jonesy
Posts: 16
Joined: Sat Oct 13, 2007 6:47 pm
Year and Model:
Location:

Post by Jonesy »

Ozark Lee wrote:The module is inset into the air duct so you will not be able to see the heat sink unless it is removed - they use the air from the cabin blower to cool the module. On the blower resistor that I had to replaced on my manual unit the assembly was held in with a single T-25 torx head screw and it was kind of a prick to get to due to a wiring harness in front of it. I used a T-20 torx at an angle to carefully remove the screw.

I think the ECC power stage is the same but I have never actually seen one.

...Lee
Got it. My unit has a resistor pack, I measured it with an ESR meter as it is such low resistance, and found that there is an open circuit in the (what looks like) thermal fuse that is spot welded in series with the resistors. When I jumper across it the fan now works. What I am still curious about is the other module nearby, it obviously has transistors in it, I would like to know what it is for...


Image


Image
Jonesy
Posts: 16
Joined: Sat Oct 13, 2007 6:47 pm
Year and Model:
Location:

Post by Jonesy »

I guess I will need to replace the entire resistor pack, I don't have a spot welder to attach a new fuse, unless silver solder could stand the temperature. I can't see the rating anyway to replace it.

Also, I am very interested still with the issue of the FET, I will ask my volvo service centre if they have a dead one and if so I will strip it and find a FET to fix it. If anyone has a dead unit let me know, maybe I can start an Exchange service for parts and postage cost only for forum members that aren't handy with a soldering iron :-)
Jonesy
Posts: 16
Joined: Sat Oct 13, 2007 6:47 pm
Year and Model:
Location:

Post by Jonesy »

OK, the plot thickens. The fuse is a Microtemp Y4A16. Can anyone read German? Here is a page that looks like someone may have figured it out, but I can't read it.

Looks like it is a Microtemp thermal safety device with a trip temperature of 216 degrees celsius, presumably it trips out to protect the resistor pack if the pack gets too hot.

This device is available for the princely sum of $1.87 plus tax.

http://www.barchetta-lexikon.de/?action ... &daten=037
MadeInJapan
MVS Moderator
Posts: 13424
Joined: Thu Mar 31, 2005 7:14 am
Year and Model: '98 S70 T5 '07S40T5
Location: Knoxville, TN American but born in Japan
Has thanked: 7 times
Been thanked: 27 times

Post by MadeInJapan »

'98 S70 T5 Emrld Grn Met/Beige Tons of Upgrades Mobil-1
'04 V70 2.5T Red/Taupe Some Upgrades Mobil-1
'07 S40 T5 AWD 6 speed manual! Silver/Black Stage1 Heico & Elevate
'07 S60 2.5T Blue/Taupe- my kid's Volvo
Post Reply
  • Similar Topics
    Replies
    Views
    Last post