Well the temperature here in MT took a big drop today and so did the performance of the High Output heater in my pickup.

When the outside air is above 60 degrees, the heater blows very hot air. Today the outside air was about 20 degrees and the heater was blowing mild air. The cab never even got warm. My temp gauge is reading on the 'O' so I think the operating temp is OK - and I just replaced the thermostat (195 degrees).

Do these heaters draw cold air from the outside all the time? Is there a plenum or something to regulate how much cold air is being pulled through the heater? Any other ideas why the heater performance is so poor?

As always thanks for the help. This is a great site!

 

How often is the heater used a year?

It sounds like there might be some corrosion from lack of use.

Try using a jumper wire directly from the battery to the motor wire & check the Fan speed when doing this.

 

Check top make sure that your cable is moving the door all of the way. Loosen the mounting screw and see if you can move the door any further.
Yes, they draw in all of their air from the outside.

Jimmy

 

'Defrost' pulls in outside air. 'Heater' recirculates.

 

I guess, I should have asked if it has A/C or not. If not, then it will pull in outside air. It is drawn in thru the passenger side vent assembly.
Jimmy

 

Dont forget to check your coolant level, the core is the highest point. Oneford

 

I jsut went through all the controls on my 77. As I recall the heater draws outside air (sort of a safety thing for carbon monoxide). The AC recirculates inside air. If your temp gauge is on the "O" or NORMAL that sounds too low.

 

Thanks for the replies.

I do not have A/C. The coolant was just replaced and the level is OK. I checked all the cables and they are operating/opening correctly. The air flow from the fan is good, however it seems like when the fan is on High the air is cooler than when it's on the middle setting. The truck came with a "super cooling" radiator (I can't remember what it was called on my build sheet) and it's always operated in the 'O' on the temp gauge.

I'm cold and stumped!

I'm going to try the "Ford Thermostat" technique (cardboard on the ol' radiator) to see if that helps.

Again, thanks for all of the help!

 

if you dont use the vent on the passanger side much in the summer, i took of the vent door and coverd over the hole from the outside and now it recirculates the air inside the cab, the drawback is it holds in a lot of moisture for the defroster so i crack the window a little, this made a world of difference in michigan when it gets below zero

 

I still suspect you thermostat isn't working correctly.

 

try flushing the heater core sounds pluged are the heater hoses the same temp? if not the core is plugged or the flow is restricted the reason the air is colder on hi is you dont have enough hot water in your heater core and the increased air flow in actually cooling the little bit of warm air you got maybe you got an air bubble in the core I put a flush tee in my heater hose and remvove the cap whenever i fill my cooling system to let the air out

 

It could have air in it. If the gauge is reading about 1/8" past the low side normal line then it is running 195 degrees. 180 is the low line of the normal range, 1/8" below the low side normal line is 160 degrees. Both of my 77's read this way.
Jimmy

 

My truck never cooled properly until I placed the T in the heater inlet line to let the air out. I run a 160 thermostat, but I am gonna change it soon, its getting awful cold up here in Maine.

I hear the Billings high is 17 degrees on Friday, thats what my dad says. Sounds like Canada is to blame again. tsk tsk tsk

 

It was 82 In Fort Rucker today, I guess I better see if the heater works before the south gets it`s two days of winter...
Yes I`m a "Darn Yankee" LOL!!

 

just a note to help some of you in regards to where the needle rides on the guage. having worked as service tech i have some very bad news for you that is first hand. the guage does not tell you how hot your engine is. ford sets the guages so that it rides in the middle and any change will arouse concern. now that being said there are various parts to the equation such as humidity, ambient temp, electrical system etc.. that affect where the needle rides. if all is well but the needle is too high or two low a tech is supposed to change the sender to one that will read where the needle should be. in other words for example a green top temp sensor will make a truck ride in the middle of the guage at 185. the owner feels that it is too hot and he takes it to the dealer to be checked out and we find everything is normal we instal a red top sender and lo and behold the truck runs cooler when he gets it back and he is happy. the reality is nothing has changed except the consumers perception. now that these vehicles are so old many senders have been changed and guages have been through a million heating and cooling cycles so now each vehicle has a slightly different comfort range. O in the northeast may be fine, my F250 rides solidly 1/4 inch from the top line at 195 here in the southwest and since i know it will ride there unless there is a problem i have not adjusted it. of course everyone including the smog techs tell me my truck is overheating though! LOL hawkrod