Repeated blower motor resistor failures

bobfope · Post by **bobfope** » 31 Jul 2018, 11:58

I have a 1995 Volvo GLT wagon and fortunately a son who is an expert auto mechanic with 20 years of experience to help me maintain it. After I first began using my AC this season I had the symptom that the AC would only work when the blower motor was set on the maximum speed, indicating that the blower motor resistor had failed. While at first, I seemed to be getting some reasonable cold air with the blower motor on maximum, I soon lost that indicating that I was losing refrigerant. We replaced the blower resistor with an aftermarket part from fcpeuro ($50), put everything back together and recharged the AC system. That seemed to solve the blower motor speed problem, it would operate under all settings. But, only a handful of days went by when the resistor failed again. I thought I had a bad part and we replaced the resistor with a Volvo part ($130). And again, that seemed to solve the motor speed control problem. During this installation my son looked at the evaporator with a light probe and declared it look messy and probably was the source of the AC refrigerant leak. To confirm this, he put a dye in the refrigerant and recharged the AC system (We still do not know the result of this test). Anticipating the evaporator would have to be replaced, he did not reinstall the airbag and other trim parts on the passenger side, but the resistor was firmly in its proper place. But again only a handful of days later the new resistor failed with exactly the same symptoms and that is where I’m at today. My son says he has had the experience of the manufacturer (not necessarily Volvo) recommending that when you replace the motor resistor you should also put a new blower motor in. The premise is that if the motor is not running exactly as specified ( e.g., turning without any undue friction) it will draw additional current that will burn out the resistor.
What I’m trying to find out here is, a consensus that replacing the blower motor in addition to another blower resistor will solve my problem or that there are other suggestions as to what is happening. I thank you for any input you can provide.

Post by **RickHaleParker** » 31 Jul 2018, 13:09

Heat is what destroys a resistor. Excess current draw produces excess heat, which would destroy a resistor real fast.

Have you cleaned out the blower cage of dead leaves and other debris that can create a excess load on the blower motor therefore, more current draw from the blower motor?

When was the last time you changed the Cabin Air Filter?

Post by **abscate** » 31 Jul 2018, 14:04

The Volvo blower is known to crap out after about 20 years, pulling excess current and blowing the transistor pack (its actually not a resistor pack like Grandpas Volvo was)

Post by **jimmy57** » 31 Jul 2018, 15:11

If the resistor fails, three things can cause it: 1. rust rots through wire (not the issue is it is pristine when removed) 2. Blower air inlet is obstructed or the evaporator is plugged with debris. If it is these things then it would not have good air volume when on HIGH. The low airflow lets the thermal fuse on resistor overheat and go open. 3. The blower motor is old and has worn bushings and the current to move it is high and the thermal fuse burns open from the resistor overheating. Blower motor full current is typically 15A or less if the blower current is checked on HIGH.

Post by **BEJinFbk** » 31 Jul 2018, 22:08

First off, yes. You may well have a worn motor
that's taking out your speed controlling device.

But, first - There are two climate control systems
available in these cars. The basic MCC and the more
sophisticated ECC, so, it would be helpful to start
with the basic question: Is your system MCC or ECC?

MCC ( Manual Climate Control ) has a 4 speed fan
control and uses an actual set of resistor wires.

ECC ( Electronic Climate Control ) has a fully variable
fan speed control, includes a switch marked "AUTO"
and uses an electronic "resistor" to control fan speed.

As there are different diagnostic steps for each system,
please let us know which one you're dealing with.

Post by **jreed** » 01 Aug 2018, 05:19

A few years back I measured the current draw of a new versus an old (squeaky) Behr blower and found that the old blower drew about half an amp (or 5%) more current at 8V compared to the new one. You could measure your blower and compare the current draw to see if it really is drawing more current than typical.
viewtopic.php?t=19322&start=103

Jaybar · Post by **Jaybar** » 01 Aug 2018, 08:59

I bought an 850 1997 at auction replaced resistor and didn't check drain line and bought another resistor and cleaned drain line. So now I charge system once a year.

bobfope · Post by **bobfope** » 05 Aug 2018, 09:13

RickHaleParker wrote: ↑31 Jul 2018, 13:09 Heat is what destroys a resistor. Excess current draw produces excess heat, which would destroy a resistor real fast.

Have you cleaned out the blower cage of dead leaves and other debris that can create a excess load on the blower motor therefore, more current draw from the blower motor?

When was the last time you changed the Cabin Air Filter?

Thanks for your response. Planning to replace the blower motor And as you suggest, the cabin air filter. I had changed it about four years ago. I have learned that there is a thermal fuse on the resistor that has apparently blown due to insufficient airflow. I'm hoping to replace that fuse and thereby save one or both of the blower resistors that I have thus far, "blown". Thanks again for your insight.

bobfope · Post by **bobfope** » 05 Aug 2018, 09:17

abscate wrote: ↑31 Jul 2018, 14:04 The Volvo blower is known to crap out after about 20 years, pulling excess current and blowing the transistor pack (its actually not a resistor pack like Grandpas Volvo was)

Thanks for your response. Planning to replace the blower motor. I have learned that there is a thermal fuse on the resistor that has apparently blown due to insufficient airflow. I'm hoping to replace that fuse and thereby save one or both of the blower resistors that I have thus far, "blown". Thanks again for your insight.

bobfope · Post by **bobfope** » 05 Aug 2018, 09:48

jimmy57 wrote: ↑31 Jul 2018, 15:11 If the resistor fails, three things can cause it: 1. rust rots through wire (not the issue is it is pristine when removed) 2. Blower air inlet is obstructed or the evaporator is plugged with debris. If it is these things then it would not have good air volume when on HIGH. The low airflow lets the thermal fuse on resistor overheat and go open. 3. The blower motor is old and has worn bushings and the current to move it is high and the thermal fuse burns open from the resistor overheating. Blower motor full current is typically 15A or less if the blower current is checked on HIGH.

Thanks for your response. Planning to replace the blower motor and also the cabin air filter (I had changed it about four years ago). My motor turns but as you suggest the air volume is low even on the highest setting. As you suggest, we suspect the problem is the evaporator is plugged up as we know now it is leaking refrigerant and will have to be replaced to fix the AC. I am assuming the thermal fuse you mentioned is the component that is mounted externally to the, "green brick of resistors" on the blower resistor part it self. The component looks like a resistor, but is not marked like one. I'm hoping if that thermal fuse can be replaced I will be able to use one of the existing "blown" blower resistor parts I have instead of having to buy a new one $50. Do you happen to know the nomenclature and how I can get another one of those thermal resistors?

Thanks again for your insight.