defrost not working

[AaronW]

All:

The blower motor on my 89 V300 recently quit on me. I installed a new one, which works fine, but now I have no defrost. Looked through the pictures on the sticky thread for this topic, but am still not clear on how to proceed. Basically, the upper slider lever on the dash, with "OFF" on the left over to "DEF" on the right, doesn't appear to do anything now. The truck has AC, if that matters. I've definitely got some sealing issues between the defrost air housing and the main one, but I should at least be getting something. The switch will turn the fan off. When you turn on the fan, air always blows through the ports down by your feet and over the trans hump, no matter what position the switch is in.

What should be my next step, do you think?

Aaron

 

[YakkoWarner]

On my 1989, I believe the top slider which selects the outlet is vacuum actuated, whereas the lower one that controls cold to hot is rod or cable actuated. So I'd start by looking to ensure you didn't break or disconnect the vacuum line that goes thru the firewall to the climate controls when you replaced the blower motor. Do you hear a slight "hiss" as you change position on the upper slider?

 

[gmbellew]

Sounds like a blend door issue. The vertical piece on the duct under the dash comes out pretty easily. Take it off and see what the problem is.

 

[AaronW]

On my 1989, I believe the top slider which selects the outlet is vacuum actuated, whereas the lower one that controls cold to hot is rod or cable actuated. So I'd start by looking to ensure you didn't break or disconnect the vacuum line that goes thru the firewall to the climate controls when you replaced the blower motor. Do you hear a slight "hiss" as you change position on the upper slider?

So I discovered that the little plastic piece that attaches to the swinging door was broken, too. when I pushed that in, I can hear a hiss, like you mentioned. Also, the plastic piece up on top, where that threaded adjuster rod is, was broken as well, so I was just running that rod by hand while I tried to figure out what was wrong. So what does hearing that hiss indicate to you?

Aaron

 

[gmbellew]

So I discovered that the little plastic piece that attaches to the swinging door was broken, too. when I pushed that in, I can hear a hiss, like you mentioned. Also, the plastic piece up on top, where that threaded adjuster rod is, was broken as well, so I was just running that rod by hand while I tried to figure out what was wrong. So what does hearing that hiss indicate to you?

Aaron

Hearing a hiss probably means that a vacuum line came off one of the servos. What setting hisses? That is the problem line

 

[75gmck25]

All the doors for plenum air flow use vacuum actuators. Only the heater blend door is cable operated by the heat slider control.

Engine vacuum is provided by a line that runs from the engine compartment, through the firewall and to the dash control. Moving the control switches engine vacuum to actuate the various doors.

Remove the glove box and the vertical plastic plenum behind it.
IIRC, there is a dual port actuator that moves that door you see inside the plenum, and also a link between that door and the door behind it. With the engine running and you sliding the controls, you will see that door move all the way toward you (which closes off the defrost flow), all the way back, or to the halfway point. And while all that is happening it is also moving a door behind it. If the link on the door is broken (common problem), it is available from several sources.

If it’s the dual port actuator that is disconnected and/or leaking, that one is on the back of the plenum, and hard to reach. I have always been able to follow the lines to the connections so I could verify the line is on the connector, but it’s too far back to see everything.

Broken factory hard line can be repaired with short sections of rubber vacuum line. Dorman also sells replacement hard line. You would need that to replace hard line that runs across behind the plenum and dash. Rubber line is too thick to easily snake in behind the dash when you have multiple lines.

 

[AaronW]

Thanks for the suggestions, all. I'll be able to get on this saturday afternoon; I expect this info will get me down the road. Will report back on what I figure out.

Aaron

 

[edgephoto]

Since you were under the hood replacing the blower motor. I would start there. The vacuum supply line goes through a grommet in the firewall

 

[Mango]

If the plastic piece is broken the blend door will not open
You can get new ones for n LMC Truck

 

[AaronW]

Amazon.com: Universal AC Heater Box Blend, Air Door Clip, Air Aluminum Door Clip, Air Conditioner Heater Door Clip for Vintage 1973-1987 Trucks : Automotive

Buy Universal AC Heater Box Blend, Air Door Clip, Air Aluminum Door Clip, Air Conditioner Heater Door Clip for Vintage 1973-1987 Trucks: Heater Blend Door Levers - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Anybody used one of these? Normally I'd be kinda suspicious of amazon, but it looks like metal, where the OEM part is plastic.

Aaron

 

[Finkaire]

BTW, A/C engages in the defrost mode. It dehumidifies

 

[75gmck25]

Seems like a high price for a very simple clip, but at least you get free shipping. LMC has the same part for $5.95, but then you have to add shipping.

 

[AaronW]

All: got one of those new billet clip/hinge deals. Just about ready to put it all back together. What is the little plastic part called, that adjusts the blower door. all the way at the left of the picture? (Where the threaded rod goes through). Mine is broken, and I don't know what the part is called, so I can find a replacement. LMC's diagrams don't show it. Alternately, I suppose I could just find the right setting, and JB weld the rod to the part of the plastic clip that's still there....

Aaron

You must be registered for see images attach

 

[Snoots]

Check your local parts store in the 'HELP' parts section.