A/C Blower

[Tim Redman]

From a critical problem to a much less critical problem, especially considering this time of year.

I've already determined that there is a micro-leak in the A/C somewhere. A refrigerant charge lasts for about six months of intermittent use, but then starts to fall after that. However, that's not the issue I'm bringing up.

I've noticed that when the fan is set to its lowest setting, any air coming out of the dash vents is almost imperceptible. On 2, 3 and 4, it blows fine. However, one thing I have observed is that the lowest setting does actually start to blow when I get up to speed. This is with the A/C on recirculate, not bringing in outside air.

Could I be looking at a vacuum leak here, not opening the damper doors all the way? I've tested for leaks under the hood, and the only thing I could find was a tiny leak at the bushing on the throttle valve of the intake manifold, which I'm told is pretty common, and is almost impossible to make go away without replacing the bushing. Even then, it doesn't last terribly long. Seems to be a normal wear item. During the leak test, I never noticed any smoke coming out of anywhere in the cab.

At this time of year, it's not a huge deal. Because it affects the A/C and heating, I almost never worry about it because if I'm using either one, they're usually cranked up to 2 or 3, otherwise the top is off. Any ideas?

 

[freedom_in_4low]

there is a resistor bank that controls the fan speed setting. The lower you turn the fan speed, the more resistance it adds to the circuit, to provide less voltage to the fan.

As resistors in that bank fail, you sequentially lose the lowest speeds first. If you lose the resistor for speed 3, you lose 3, 2, 1. If you lose the resistor for 2, you lose 2 and 1. Sounds to me like you've lost the resistor for speed 1. It blows when you get up to speed because the aerodynamics of the TJ (and most vehicles) creates a high pressure zone in front of the windshield, above the cowl, where the HVAC air gets pulled from. That high pressure zone pushes some light airflow through the fan and HVAC box in spite of the fan not running.

All that to say, I believe you need a blower motor resistor. Mopar part is 5139719AA, you can also find them at the retail parts stores but buy their parts at your own risk.

 

[Tim Redman]

there is a resistor bank that controls the fan speed setting. The lower you turn the fan speed, the more resistance it adds to the circuit, to provide less voltage to the fan.

As resistors in that bank fail, you sequentially lose the lowest speeds first. If you lose the resistor for speed 3, you lose 3, 2, 1. If you lose the resistor for 2, you lose 2 and 1. Sounds to me like you've lost the resistor for speed 1. It blows when you get up to speed because the aerodynamics of the TJ (and most vehicles) creates a high pressure zone in front of the windshield, above the cowl, where the HVAC air gets pulled from. That high pressure zone pushes some light airflow through the fan and HVAC box in spite of the fan not running.

All that to say, I believe you need a blower motor resistor. Mopar part is 5139719AA, you can also find them at the retail parts stores but buy their parts at your own risk.

I've been reading similar things as well. From what I understand, there's a simple ohmmeter test for the unit. I'll give that a shot. Thanks.

 

[Jerry Bransford]

If your resistor pack has gone bad be sure to replace the fan motor too which is the root cause of the resistor pack going bad. The fan motor windings commonly start shorting together when the shellac insulation starts breaking down. That causes the fan motor to start drawing excessive current (amperes) through the resistor pack, wiring sometimes melting its insulation, and fan switch. The fan switch isn't always damaged but it happens

 

[Tim Redman]

If your resistor pack has gone bad be sure to replace the fan motor too which is the root cause of the resistor pack going bad. The fan motor windings commonly start shorting together when the shellac insulation starts breaking down. That causes the fan motor to start drawing excessive current (amperes) through the resistor pack, wiring sometimes melting its insulation, and fan switch. The fan switch isn't always damaged but it happens

Sometime before the spring, I'm going to have a local guy pull the dash to take care of a tiny leak in the system. There's going to be several pieces I'm going to have him replace while he's in there. So much of the expense is going to be the labor of taking the dash off to get to everything, so while he's in there, I might as well put him to good use.

 

[Tim Redman]

there is a resistor bank that controls the fan speed setting. The lower you turn the fan speed, the more resistance it adds to the circuit, to provide less voltage to the fan.

As resistors in that bank fail, you sequentially lose the lowest speeds first. If you lose the resistor for speed 3, you lose 3, 2, 1. If you lose the resistor for 2, you lose 2 and 1. Sounds to me like you've lost the resistor for speed 1. It blows when you get up to speed because the aerodynamics of the TJ (and most vehicles) creates a high pressure zone in front of the windshield, above the cowl, where the HVAC air gets pulled from. That high pressure zone pushes some light airflow through the fan and HVAC box in spite of the fan not running.

All that to say, I believe you need a blower motor resistor. Mopar part is 5139719AA, you can also find them at the retail parts stores but buy their parts at your own risk.

I was able to source a MOPAR resistor pack from a dealership a couple of counties away that acts as our regional distributor. Actually, with shipping, it still turned out to be slightly cheaper than getting the same part from someplace like Quadratec, which was estimating at least 2-3 weeks delivery. Should be in the middle of next week. I've seen the process to replace it, and I don't think it'll be a big deal, just a reasonable pain in the ass.

 

[freedom_in_4low]

I was able to source a MOPAR resistor pack from a dealership a couple of counties away that acts as our regional distributor. Actually, with shipping, it still turned out to be slightly cheaper than getting the same part from someplace like Quadratec, which was estimating at least 2-3 weeks delivery. Should be in the middle of next week. I've seen the process to replace it, and I don't think it'll be a big deal, just a reasonable pain in the ass.

Nice. It's mostly just awkward body position, nothing completely terrible like the heater core.

Jerry's advice is sound....I've replaced a couple of these resistors without replacing the fan and I haven't had issues but logically it's a good move based on all the melted and charred connectors I've seen here. And at least on our late models the blower is ridiculously easy to replace.

 

[Dr. Internet]

In addition to what Jerry says, you might not have a leak. Your AC system is full of seals and the refrigerant includes lubricant, or oil. If, like I used to do, you don't run your AC, the oil does not circulate and the seals dry out and start to leak. Now, based on advice from an auto HVAC expert, I run my AC once a month for at least five minutes. No problems in the last five years.

 

[Tim Redman]

In addition to what Jerry says, you might not have a leak. Your AC system is full of seals and the refrigerant includes lubricant, or oil. If, like I used to do, you don't run your AC, the oil does not circulate and the seals dry out and start to leak. Now, based on advice from an auto HVAC expert, I run my AC once a month for at least five minutes. No problems in the last five years.

The leak was confirmed by a pressure test, at least going by what the shop told me. I don't know them well enough to know whether or not they're trying to gouge me, which is why I had them just recharge the system and let it go for a while to see how long it lasts.