Passenger fan slowing down?

[allegro]

My passenger's side climate control fan/blower seems to be slowing down - in auto or manual climate modes, the passenger's side blows noticeably less air than the driver's side.

Any ideas on whether I should try the blower motor or the resistor first? This thread gives good info on r/r but I'm not sure what to try first in my case. There are no strange sounds, smells, or other failures, just weak air.

Thanks for any ideas.

 

[jlglr4]

I believe there is only one blower motor for both sides of the system. I think the setup is as follows: The single blower has two outlets - right and left. Each outlet has a separate temperature blend door. Then each side has several distribution doors for controlling flow to the windshield, face, or feet according to the selected options on the controller. And, each vent has a manually operated closure to regulate how much air comes out of the vent (little dial below each vent).

So, if it’s blowing well on one side but not the other, I would first check to make sure all the vents are open to the same degree using the little dial at the bottom of each vent (even in the back, as open vents in the back will - I think - lessen distribution to the front). If everything is the same on both sides, and still the passenger airflow is low, then perhaps its a distribution door issue. Maybe check to make sure you‘re not getting air someplace you don’t expect it (e.g., if you‘ve got it set to **** on your face, check the floor or windshield on the passenger side to see if it’s coming out somplace it should not be, which might indicate a distribution door motor issue). Or maybe the distribution doors are all closed on the passenger side when one should always be open, i.e., a door stuck or a door motor not responding.

 

[allegro]

Thanks for the reply, and of course it makes a lot of sense that the system would have a single blower motor.. doh! I had checked the manual vent dials up front but hadn't looked further back. Will give that look as well as check for any evidence of a distribution door issue. More soon.

 

[ryanjl]

When I was troubleshooting my blower issue last summer, I had read some things that stated a bad blower resistor can cause some weirdness with the blower speeds or controls. But I would think that would be overall, and not left or right.

 

[allegro]

Hmm.. I did some pseudo-science today with an IR thermometer and found the passenger vents to be blowing air that's consistently 10-15 degrees warmer than the driver's side air. To test I put the climate controls in "LO" mode and then tested one face vent at a time with everything else closed up. It feels like the air flow is somewhat lower in the passenger vents as well, but it might just be the perception of less flow from the warmer air.

Unless anyone knows offhand how the blending system works and how to test/troubleshoot it, I'll start doing some digging in repair manuals. I wonder if there's any chance that the blower resistor could cause blending issues..

 

[allegro]

The deeper I get on this one, the more confused I get. I think I've ruled out the passenger temperature blend actuator - I removed the actuator and verified that the motor moves when I change the passenger temp via the dial. I also manually opened and closed the flap/door by twisting the little gear that the actuator attaches to and verified hot air at one extreme. However, I also verified that when the blend door is at the other extreme the air is not as cold as it is on the driver's side. I also recalibrated the stops on all the actuators with the GAP tool, but I didn't notice any difference.

Here's a workshop manual diagram of the airflow through the heater:

Given what appears to be uniformly cooled air entering the main chamber of the heater assembly, I'm wondering if I could either have a physical issue with the passenger temp blend door that is allowing air to pass by and be heated, or perhaps some kind of blockage at the a/c evaporator that is restricting the flow of cold air into the passenger side chamber.

As far as I know, the only way to get in there for a closer look would involve removing the whole dash, so I will continue to search around and scratch my head with this one for a while.

 

[greiswig]

Long shot, but... I've had mice nest in air ducts before, and create blockages. Usually you smell it, too, though. But maybe putting a vacuum on the vent to try to force a fair amount of flow through the system would help?

Also, check the cabin air filter, or just remove it temporarily and see if that seems to help. Probably want to remove it anyway if you're going to try to put the vacuum on things.

Another possibility: are you sure it hasn't ALWAYS blown less on one side? The length of the ductwork, etc., affects the flow, so maybe just balancing the flow at the vents is what was always needed, but you just noticed it?

Just thinking aloud...

 

[allegro]

Update: after testing the low and high side pressures of my a/c system using a a/c manifold gauge set, I found both pressures to be pretty low. From my research, this tends to indicate a low charge of refrigerant. Next step will be to have a good shop do a full discharge and recovery, leak test, and recharge with the correct weights of refrigerant and oil.

With my trusted shop a couple hours away, I decided to add a little refrigerant to see if the pressures recovered at all. I added nearly a 12oz can of "pure" refrigerant (not the ones with stop leak, or added oil, etc) via the manifold gauge set to bring the pressures up closer to the generic ranges I found for r134a at a given ambient temp, and I am cautiously optimistic about the results. Following this procedure, the driver and passenger temps are nearly identical... and also a good 10-15 degrees cooler than before.

I may try adding some UV leak detecting dye myself to do a little more troubleshooting before handing it off to a shop, just in case it reveals something silly like a slow leak in an under-hood hose connection. It's interesting to get a little deeper into how the a/c system works, but my curiosity is outweighed by my terror of causing damage by overcharging the system or introducing air/moisture/debris.

On the bright side, I learned that the Gap IID tool was super useful for this a/c troubleshooting:
* air blend motor position
* air distribution motor position
* a/c high side pressure
* evaporator temp

It was also helpful to quantify a/c performance changes by setting thermostat at LO, selecting face vents only on the lowest blower setting and fresh air input (not recirc), and then recording temp of each vent output (both in absolute terms and as a delta off of ambient).

I'll add more here when a shop gets their hands on the truck and tells me what's really going on... until then, thanks for the help moving this one along!