Vents change just fine but no heat

[renjaminfrankln]

My new to me '89 F250 has some issues with the heat/AC. The AC compressor clutch/bearing is blown but that is an issue for another day. With fall upon us I decided it may be time to get some heat working.

The vacuum lines in the engine compartment look okay and the brakes work fine. The vents will switch from floor to dash to defrost as you select them. However it blows in outside temperature air, even with full heat selected. The heater core does not leak and the coolant hose routing to it looks fine.

Obviously the blend door that controls the heat/ac mix is not operating. I'm sure this is a door somewhere with a vacuum actuator on it. Where can I find this thing exactly, and any troubleshooting tips?

Thanks!

 

[laserjock]

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Check the vacuum line on the actuator at the pass side back and make sure it’s attached. If it’s broke off, cut the loom back and put a piece of hose in.


The temp door may be cable pull depending on year.

 

[renjaminfrankln]

Will do. Looks like that has already been done (cut back and nylon hose added).

Don't have the truck right now its in the shop getting the front leafs, shackles and front end parts replaced + alignment. But i'll check on that this weekend. Now that you mention it the temp door does feel like it could be cable pull.

 

[laserjock]

89 should be. I don’t think it went to vacuum until OBS (92). @nomufflers can tell you. He actually did the heater control swap from brick to OBS. There is a thread here somewhere. Maybe in the tech articles.

 

[renjaminfrankln]

89 should be. I don’t think it went to vacuum until OBS (92). @nomufflers can tell you. He actually did the heater control swap from brick to OBS. There is a thread here somewhere. Maybe in the tech articles.

Yep I found some pics online of the heater control unit and it is definitely cable operated. Suppose my first job is to crawl under the dash and locate the cable.

 

[snicklas]

Hate to ask an obvious type question, but is coolant actually reaching the heater core? In my IDI and the son’s s-10 blazer, the heater cores are completely bypassed. The IDI is leaking and his heat won’t shut off, so a hose has been pulled from the core and looped back to prevent a leak.

Is there a shut off valve in the heater line? Is there enough coolant in the system? Sometimes it’s something simple...... no hot water in, no hot air out.......

 

[renjaminfrankln]

Heater hose routing is correct (I am familiar with the bypass) and no shut off in any of the lines. Next time I think about it i'll grab the hoses and make sure they are getting good and hot.

Coolant sits about 1.5" down from the top of the radiator when cold. It might could use a bit more coolant but it is not very low. I'm going to put in new heater hoses this weekend and get an SCA reading after I top it up.

 

[IDIBRONCO]

Next time I think about it i'll grab the hoses and make sure they are getting good and hot.

That was going to be my suggestion. It does happen. Also, how's your thermostat? When I got my current 85 F250, the thermostat was physically stuck open by a piece of threaded metal. The factory temp gauge read a little low, but it put out no heat at all. It wasn't too bad by the time it reached 50 outside. From the looks of it, I'm guessing that it was a broken off piece of an old glow plug controller.

 

[nostrokes]

Yep I found some pics online of the heater control unit and it is definitely cable operated. Suppose my first job is to crawl under the dash and locate the cable.

Pull the glove box and the cable is front a center right on top of the heater box easy peasy... You can operate the lever and watch the cable at the same time. If it seems the door isn't moving all the way you can pull the core cover and try to see if there is something blocking it.

Definitely check the hoses and make sure they are getting hot, also put your hand on the core cover and feel for heat there too.

 

[sjwelds]

Pretty sure the door in my '92 is cable operated. IIRC it was stuck when we got it, so we disconnected the cable and swung the door so we'd have heat (truck didn't have working AC at that point). Since then we got it all fixed and got the AC working.

 

[renjaminfrankln]

Thanks for all the tips. This should be easy to troubleshoot.

Tstat is good, warms up quickly and maintains a constant temp. Previous owner replaced it.

 

[renjaminfrankln]

Alright alright alright

It was the cable. The cable visibly looked fine, but it was super hard to move. The cable mount broke off at the heater control unit. The plastic on the cable itself broke. This is because the cable was so sticky.

I was able to free the cable up by cutting tiny slits in the housing with a razor and working WD 40 in. Right now I can operate it by hand and i'm looking for a new cable... I could reinstall this one with some JB weld but if it seized up again in a year or two, i'd be looking for a new heater control unit.

If anyone knows where to find a 'new' cable let me know!

 

[laserjock]

Word of caution. WD can cause problems in very cold climates.

Might try Rock auto. I’m amazed at some of the random stuff they have. I’m sure ford made a billion of that cable. It was used in a lot of trucks. Probably other things too.

 

[renjaminfrankln]

Haven't had any luck finding one. Might try to rig up a cable luber. I have one somewhere from my motocross days.