Heater: driver side not as hot as passenger side

[kaspr]

I have a '95 P.A. with dual zone automatic climate control. When I turn the heater on, the driver side is not as hot as the passenger side. I have checked the actuators and blend doors, and both the driver side and passenger side do indeed go to full hot, so I know it's not the HVAC programmer or actuators at fault. Should I suspect a leak in the ducting to the driver side, or that the driver side blend door isn't sealing? Or could it be something else?

[Blue Bowtie]

You've obviously done your due diligence and homework. Since the blend actuators (both upper and lower) are stepping to their full hot positions, about all that is left is mechanical damage to ducting, dampers, or poor sealing of the dampers. 15 year old foam rubber may not seal as well as it did 10 years ago. I had a similar thing with my '95 LeSabre, but on the opposite side. The actuators worked fine and the application of some new self-adhesive weatherstrip foam (the kind used to seal exterior building doors) worked well enough to get it to seal out the cold, unconditioned air.

[kaspr]

Blue Bowtie, what exactly did you use the weatherstrip foam on?

I've done some more tinkering and have found that the driver side is cooler at any temperature that heat is commanded (full heat or mild heat). When room temperature air or cool air is commanded, the temperatures are the same on both sides. Also, this difference exists at all levels (floor, mid, windshield). At first I was thinking it was the foam that seals the blend door hot position, but now I'm thinking that's not the case because it's not just the full hot position where the difference in temperature exists, so cold air is getting into the driver side more than the passenger side even when the blend door is not completely in the hot position. That should negate the idea that it's the foam seal on the blend door, right? I'm thinking somehow cold air is getting in after the blend doors but before the valves that tell the air which level to go to. Any ideas? Also, how do I access the problem area?

[enslow]

Originally Posted by kaspr

Blue Bowtie, what exactly did you use the weatherstrip foam on?

I've done some more tinkering and have found that the driver side is cooler at any temperature that heat is commanded (full heat or mild heat). When room temperature air or cool air is commanded, the temperatures are the same on both sides. Also, this difference exists at all levels (floor, mid, windshield). At first I was thinking it was the foam that seals the blend door hot position, but now I'm thinking that's not the case because it's not just the full hot position where the difference in temperature exists, so cold air is getting into the driver side more than the passenger side even when the blend door is not completely in the hot position. That should negate the idea that it's the foam seal on the blend door, right? I'm thinking somehow cold air is getting in after the blend doors but before the valves that tell the air which level to go to. Any ideas? Also, how do I access the problem area?

How's the flow through the heater core?

If I've got it right, the lower half of the heater core warms the passenger side and the upper half warms the drivers side. If the coolant flow through the core is slow enough, all the heat would go into the passenger side air not leaving any for the drivers side.

[Blue Bowtie]

I cleaned up and resealed all the dampers I could access when I changed the heater core. I also had to remove the blower changed the resistor, so most of the system was wide open. I had some difficulty with the RH (upper) damper motor and worked that over as well. Between all the activities (new core, new resistor, repaired damper motor, new weatherstrips) the problem was solved.

Before replacing the core and sealing the doors, manually disconnecting the actuator linkage from the nylon clip and moving it full hot still didn't solve the issue.

I was able to get to most of it through the glove box opening:

[Blue Bowtie]

Originally Posted by enslow

How's the flow through the heater core?

Excellent point. Even though the access outside the firewall isn't great, perhaps switching the hoses to reverse coolant flow might clean out the core and answer that question.

[kaspr]

Thanks both of you! I suspect that flow is too slow in the heater core. I'm going to switch the hoses and see what happens, and I'll let you know. Hopefully there's just crud built up that will come loose. It may also be that I do have a problem with dampers not properly sealing in the drivers side duct after the blend door and before the valves for upper/mid/lower vents. But the heater core seems much more likely to be the culprit.

[kaspr]

OK, I switched the heater hoses, and now the driver side is slightly hotter (which is opposite of what it was before), though both sides are now less hot than the passenger side used to be before I switched the hoses. So I've definitely got restricted flow through the heater core. What is the solution, besides replacing it?

Will backflushing help? Should I put apple cider vinegar in the system first (I've heard that works better than radiator flush)?

Any other ideas besides replacing the heater core?

Any advice on how to replace the heater core? Do I access it from behind the glove box? How do I take off the heater hoses? It looks impossible to access the clamps on the firewall, especially on the lower hose. Do I need a special tool?

[enslow]

When I changed my heater core, I found it wasn't bad. Most of the time was spent looking on the internet for advice, and comparing it to my FSM. I don't know about the Park Ave, but I found that a small stubby ratchet and my skinny hands were very helpful.

What I learned:
If you have dual climate control, removing the vacuum line control adapter was tough, and I broke the plstic nipples. I drilled out the nipples and used vacuum line hose to splice the vacuum lines.

I bought a hose clamp remover for $50 from KMS for the heater hoses. Best money I spent. I replaced the clamps with screw type because they were easier to install. Just make sure you don't overtighten. You can always tighten more after, but you don't want to crack to pipes.

I used an OEM core. It came with new foam. I'm not sure how good aftermarket cores are, or if they come with sealing foam.

[enslow]

Second thought:

You could try flushing the core, but if it didn't flush when you swapped hoses, I don't know if I'd risk using higher pressure or not. I've heard some manufactures install restrictors to reduce the water pressure inside the cores so they don't blow. To me, that suggests that flushing the core might come with a risk of blowing the core. I suppose you could try and then keep an eye on it.

[kaspr]

Will be back-flushing the cooling system and especially the core, this weekend. Thanks for the tip about going easy on the water pressure. If that doesn't fix it, I'll get a new core installed. At least I've narrowed it down to the core and know it's not the electronics or ducting.

[kaspr]

I backflushed it several times, and now the heater is much better, so I won't have to replace the core. The heater works best with the hoses reversed, so that's how I'm leaving it. Thanks everyone!