My '94 F-150 5.0 is producing very little heat. I have read many of the existing threads and am still confused.

To begin, I had a 'bouncing' temp guage, a check engine light, and no heat. I have replaced the water pump (which cured the bouncing temp guage), the thermostat (twice), the radiator cap, the heater hoses, the heater core, and a vacuum motor which sits atop the blower assembly. Auto Zone tells me the check engine light is a 332 code, which they said has nothing to do with heat.

The vacuum motor I replaced (based on a NAPA guy's advice) seems to open an air flow path when it extends, and seems to somehow control the flow of coolant through the heater hoses. When it is extended, the door is open, but the heater hoses go cold, when it is contracted, the door is closed and the heater hoses get hot. This confuses me, as turning the heat to 'Off' causes the motor to contract, and 'On' causes it to extend. I am currently running with the motor taped in the contracted position and disconnected from the door, plus the door taped open. This gets me medium heat if the selector is on "vent', less heat on 'floor' and no heat on 'defrost'.

I can see three vacuum motors under the dash, and they all move things, I hope correctly. The truck runs in the lower normal range, consistantly since the water pump replacement. I am not lOsing coolant. There is pressure released if I crack the radiator cap after driving. The system was flushed in the spring.

Can anyone tell me what that vacuum motor has to do with coolant flow? And, why the coolant flow and the door seem to be out of sync?

 

wrong vacum moter?installed backwards? and check the blend door, good luck,bob

 

Thanks for the prompt response.

The vacuum motor is exactly like the old one, and there is only one way to install it. Vacuum hose on the back, metal rod out the front. I still don't understand how compressing that motor results in coolant flow in the heater hoses.

I guess that leaves the blend door. Does that mean pulling the whole assembly out from under the dash? I have both the Hayes and Chilton manuals, and neither of them mention the blend door (or anything about vacuum motors).

 

do both heater hoses get hot? if you lay on the floor and move the heater / defrost switch , do you hear the blend door move if not there is a linkage that you can move by hand .you should be able to manually move the blend door one way or the other, if that gives you heat you may have a bad controller, bob.

 

Both heater hoses get hot if the vacuum motor on the blower assembly is "compressed". When laying on the floor moving the heat/defrost ****, I can see a different vacuum motor moving, and the air flow changes, but I wasn't trying to listen for a door moving. In case I can't hear it, where is that linkage you mentioned?

Thanks for the help.

 

is it possible you have the hoses reversed ? does your defroster work? theres a few posts in this forum on how to repair blend doors , the vacum motors may be moving but they may not be actuatung any thing inside the box, good luck,bob

 

The hoses are currently from the front of the engine to the connection farthest from the fender, the connection closest to the fender goes to the water pump, there is a tee just before the water pump, from which a smaller hose goes up to somwhere near the EGR valve. I think this is correct, but I am considering swaping them for the drive home to see what happens.

The defrost, floor and vent settings do result in air flow from the correct places. I won't have a chance to get in there to look for broken doors until the weekend.

Thanks again for the information.

 

if you have air coming from the correct places your blend door is fine, this next idea is just a fix to get you heat , but is it possible to bypass that controller and hook the hoses direct to your heater core?,from what youve said ,you should have heat somewhere, good luck , bob

 

Thanks for the good news about the blend door. I was not looking forward to trying to tear that apart.

The heater core has two tubes from the top which extend through two holes in the firewall. The heater hoses are connected directly to those tubes. That is why I am so confused as to how a vacuum motor that is about a foot away from the heater hoses has any effect on coolant flow in the hoses. The quick fix to get some heat is that I have taped that vacuum motor in the compressed position, and taped the door control cam in the position it would be with the vacuum motor extended. This gets me enough heat to keep from freezing.

The other end of the heater input hose connects to an assembly which is also where the temperature sending unit attaches. The feed line for that loop of smaller hose, which goes up near the EGR valve, originates there as well. Could this assembly be where the coolant is being stopped? The sending unit isn't also a control unit is it?

 

thats possible , im more inclined to think tour problem is under your dash . if that area had a problem your truck wouldnt run right,. just out of couriosity was there a piece of foam insulation in the heater core area.?

 

Yes, There was a piece if foam accross the top front that tucked in along the sides. I put it back in, and I bought weather stripping to reseal around the cover when I reinstalled it.

 

I also have a 94 F-150 with a 351. There is very little heat and I had the 332 code checked today. I am not sure what the problem is.

 

one last check that youve probably already done is to pull the heater hoses and see if there is flow with the engine turning over. my other question is, what is the 332 code for , if we can identify that and eliminate it , it may point us in the right dirrection?bob

 

I don't remember the exact verbage, but it has to do with the EGR valve and/or sensor. Something about insufficient flow.

 

I feel your pain. I have a 92 F150 with mediochre heat. I just changed the vacumn motor like you. Didnt seem to make any difference. But mine was bad anyway wouldnt move when you pulled vacumn on it. The ford parts guy printed out the inside and outside breakdowns for me. That motor has NO effect or connection with the water flow. It just moves a door that I assume isolates the heater core when you run the A/C. Both my hoses are warm but not extremly hot. It has a new pump, and had 2 new tstats (195deg). My next step is a direct flush of the core. The post on here about the blend door problem doesnt seem to apply to the older trucks. It refered to "newer" trucks. Does any one know if there is an adjustment on the blend door for the 92-95 trucks? BTW I have my radiator 85% blocked and it didnt make a bit of difference in the temp gauge it stays on the south side of N.