Bruno2 Posted June 8, 2020 Author Share Posted June 8, 2020 The temperature blend door is cable operated on these trucks. Vacuum operates the mode and recirculation doors only. It sounds like you have two separate problems. Loss of vacuum will send all of the air to the defroster. This is a safety feature in case of malfunction - you'll still be able to see where you're going... The plastic lines get more brittle with age, and the white tube to the recirc door is especially prone to disintegrating with age. They will usually just crumble if you pinch them. Replace/repair as necessary with small diameter rubber hose as recommended earlier. Update: The cable and actuator is moving fine. I suppose it's the blend door itself. What does it take to get to it? The vacuum problem was the fresh air/recirc line broken again. That is fixed good enough to last for a few days. At least I know what the problem is with the vacuum. Link to comment Share on other sites More sharing options...
Gary Lewis Posted June 9, 2020 Share Posted June 9, 2020 Update: The cable and actuator is moving fine. I suppose it's the blend door itself. What does it take to get to it? The vacuum problem was the fresh air/recirc line broken again. That is fixed good enough to last for a few days. At least I know what the problem is with the vacuum. Well, that's a big improvement. I don't know about the blend door. Maybe Bill or someone else does? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 9, 2020 Share Posted June 9, 2020 Well, that's a big improvement. I don't know about the blend door. Maybe Bill or someone else does? Gary, the blend door is right behind the heater core. You can see that from the pivot. So, Brandon, you're thinking it just needs a new seal? ETA: have a good look at the seal going through the firewall. If you're losing all the air to under the hood it is going to seem hot. My cable sheath has slipped in its little clip atop the flange of the box before, but you say you can see the door working, sooo. Link to comment Share on other sites More sharing options...
Bruno2 Posted June 9, 2020 Author Share Posted June 9, 2020 Gary, the blend door is right behind the heater core. You can see that from the pivot. So, Brandon, you're thinking it just needs a new seal? ETA: have a good look at the seal going through the firewall. If you're losing all the air to under the hood it is going to seem hot. My cable sheath has slipped in its little clip atop the flange of the box before, but you say you can see the door working, sooo. Jim, I am not sure. I changed the evap core when I did the AC job. Now I have had a few of these apart over the years to wash them out. I dont tnink I damaged the door. I know the box is sealed. I put weather stipping around the seams an coiled some backer rod around the evap tubing. The only place air is escaping is where the rubber hose comes out to drain the box. I tried to feel around the mechanism that operates the door, but couldnt feel a pin for a hinge to see if it's actually moving the full range of motion. I think it's moving some just not the full range. There is no vent temperature change from hot to cold. I have the heater core shut off so it won't blow hot regardless. Link to comment Share on other sites More sharing options...
85lebaront2 Posted June 9, 2020 Share Posted June 9, 2020 Jim, I am not sure. I changed the evap core when I did the AC job. Now I have had a few of these apart over the years to wash them out. I dont tnink I damaged the door. I know the box is sealed. I put weather stipping around the seams an coiled some backer rod around the evap tubing. The only place air is escaping is where the rubber hose comes out to drain the box. I tried to feel around the mechanism that operates the door, but couldnt feel a pin for a hinge to see if it's actually moving the full range of motion. I think it's moving some just not the full range. There is no vent temperature change from hot to cold. I have the heater core shut off so it won't blow hot regardless. Brandon, If I remember correctly the inside assembly (heater core and ducts) have to come out to actually repair/replace the blend door. Blend door in cold position: Blend door in warm position: These are from the firewall side of the inside assembly. Link to comment Share on other sites More sharing options...
Bruno2 Posted June 9, 2020 Author Share Posted June 9, 2020 Brandon, If I remember correctly the inside assembly (heater core and ducts) have to come out to actually repair/replace the blend door. Blend door in cold position: Blend door in warm position: These are from the firewall side of the inside assembly. Bill, the only way I can imagine being able to view the operation of the door is to open the box from under the hood. Maybe I can see past the evap core or manipulate it to see what's going on? Link to comment Share on other sites More sharing options...
85lebaront2 Posted June 9, 2020 Share Posted June 9, 2020 Bill, the only way I can imagine being able to view the operation of the door is to open the box from under the hood. Maybe I can see past the evap core or manipulate it to see what's going on? Brandon, first, remove the glove box, on the 1987-91, I believe you open it, depress the stops and it swings all the way down and unhooks. With it out of the way you can see the top of the blend door and either a lever where the cable goes or a cam the cable operates that moves the lever on the blend door. If all this is intact then you will need to look inside. I have found that if you vent the radiator, then reinstall the cap, you can remove the heater hoses and prop them in the area behind the right hood spring. After that, remove the cover from the inside assembly and take out the heater core. You can now see the blend door from the back side. When the door closes the opening from the heater core you are in "cold", with it opened away from the heater core you are in "hot". Link to comment Share on other sites More sharing options...
grumpin Posted June 9, 2020 Share Posted June 9, 2020 Vacuum loss while accelerating is most likely a vacuum leak. Well not really. There should be a check valve between the vacuum supply and the holding tank to keep this from happening. My check valve is in place but is bad and at times I can hear the air flow change where it is going. So just because the valve is in the line check to make sure it is working. And yes that tin can can also rust out and cause a vacuum leak, been there done that also. Dave ---- With a leak the vacuum tank can only do so much. I had a small leak on the recirculating door plumbing on my Bronco and it would show up on long climbs in the mountains. Had a big leak on my truck, hose knocked off by a mechanic, and it would catch up and go to vent, but any acceleration and it would go back to defrost. Link to comment Share on other sites More sharing options...
FuzzFace2 Posted June 10, 2020 Share Posted June 10, 2020 Vacuum loss while accelerating is most likely a vacuum leak. Well not really. There should be a check valve between the vacuum supply and the holding tank to keep this from happening. My check valve is in place but is bad and at times I can hear the air flow change where it is going. So just because the valve is in the line check to make sure it is working. And yes that tin can can also rust out and cause a vacuum leak, been there done that also. Dave ---- With a leak the vacuum tank can only do so much. I had a small leak on the recirculating door plumbing on my Bronco and it would show up on long climbs in the mountains. Had a big leak on my truck, hose knocked off by a mechanic, and it would catch up and go to vent, but any acceleration and it would go back to defrost. I am pretty sure it is the check valve as it did not "check" when I tested it. The only plastic line I have left is inside the truck and it was in pretty good shape. I also know the tin can is not leaking as I "sealed" it. Dave ---- Link to comment Share on other sites More sharing options...
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