89 TC cool/heat problems

[RVdually]

I just purchased an 89 TC that has several problems. Here I will discuss one and do the others one at a time under their own threads.
The problem is that the heater works fine when first set to max heat and not moved from that setting. It almost runs you out with so much heat, but then the fan slows and it goes to mild heat only. I changed out the sensor module located over the glove compartment, under the dash cover with one from a boneyard that had a date of 1992 on it - a lot of wear time (mine was dated 1988).
When it is putting out super heat, if you slide it to max cool then back to max heat, it returns to mild heat output only, not hot heat! This makes me think that I need to buy a new one at Ford for $52.00. What gets me is that both my old one the the boneyard one do the same thing, which COULD be a coindence considering their ages and long useage.
Also, the air conditioner usually doesn't work when it is warm out. It has worked at some times, and some times not. I don't know if this is related to the heat problem or not, though.
Anyone have any suggestions for me?
I have been reading that it could be the valve on the heater hose line that I can remove the connector and short the two wires together. In the floor mode the blower does not work, which could be part of this problem, or problem number 3??? I read that when the two wires are shorted together, the fan works in the floor position. I think I have to plug the vacuum lines also.
Thank you in advance...

[Ivan D.]

You know you have an automatic climate control right? How that works is you set the temperature you want in the passenger compartment, and the HVAC system takes care of the rest - when you want max heat you will first get hot as hell air coming from the air vents, then as the ambient tempreature approaches the one set by you the blend door will start to let some cool air in to balance the heat blasting from the heater core. The car will be playing with the blend door mixing hot and cold air in an attepmt to maintain the temperature you requested, and it's all pretty efficient if you don't have vacuum leaks. If the fan is set to auto it will follow the same logic as well, spinning fast in the beginning and progressively slowing down when the desired temperature is reached.

On the A/C subject - if you have the vent selector lever set to "Panel" or "Hi-Lo" the compressor will run as those are the selections most often used when cold air is needed. Running the compressor at the same time as the heat also achieves the effect of drying the air, so if you put the vent selector lever to "Defrost" you should notice the compressor kicking in again. There is no manual override for the A/C compressor, so if you do not want it to run and kill your gas mileage you can either install a bypass switch yourself, or just unplug the harness from the compressor's electric clutch mechanism.

[joedogg]

You know you have an automatic climate control right? How that works is you set the temperature you want in the passenger compartment, and the HVAC system takes care of the rest - when you want max heat you will first get hot as hell air coming from the air vents, then as the ambient tempreature approaches the one set by you the blend door will start to let some cool air in to balance the heat blasting from the heater core. The car will be playing with the blend door mixing hot and cold air in an attepmt to maintain the temperature you requested, and it's all pretty efficient if you don't have vacuum leaks. If the fan is set to auto it will follow the same logic as well, spinning fast in the beginning and progressively slowing down when the desired temperature is reached.

On the A/C subject - if you have the vent selector lever set to "Panel" or "Hi-Lo" the compressor will run as those are the selections most often used when cold air is needed. Running the compressor at the same time as the heat also achieves the effect of drying the air, so if you put the vent selector lever to "Defrost" you should notice the compressor kicking in again. There is no manual override for the A/C compressor, so if you do not want it to run and kill your gas mileage you can either install a bypass switch yourself, or just unplug the harness from the compressor's electric clutch mechanism.
Won't the VENT setting with the heat turned to max heat the air but not run the compressor, rather just vent to the outside?

[RVdually]

I would think that the vent would bypass the compressor, but I haven't gotten that far yet.
The car does have the climate control and I have been reading about it. When it is cold out, I have put the control on vent and the heat setting to max heat (85 or so in the red). After a short time, it does put out real GOOD heat, then the fan slows down as normal. BUT then, the air cools and stays cool giving me a fairlyl chilly ride from there. I even opened all the doors when it was 30 degrees and it still puts out only cool air. I am going to try pulling the plug off the thermal sensor on the heater hose in awhile and see if it works better tonite coming home from work. Doing that, from what I have been reading, should make the "floor" setting fan mode work, which at this time does not. Strange.
As far as the ac goes, it was hot when I got the car, August. At first the ac would work fine when set to the left in the blue. The fan slowed down when it approached the set temp. Then suddenly it worked until it got to the set temp, then put out only warm air. Once in a while, the compressor would kick on and cool the car, but then it returned to warm air once it got to the set temp. Right now in Missouri, it is too cool to check the ac out, but I am hoping that when I get the heater fixed, the ac will be part of that system and also function again. The "floor" setting was the same when running the compressor, the fan did not work. I thought that the entire control was bad. I bought a complete assembly from a boneyard the other day because of the dead floor system, but I am reading that that problem is being caused by the thermal switch on the heater hose. I will let you know tomorrow how that came out. I hope I don't break it as it says it is plastic, and those plugs just don't want to come off easily.
I am hoping I don't have a vacuum leak. When you go up a hill the fan slows down and you can hear the system changing doors inside the dash. Again, I hope this is all related.

[RVdually]

I got the plug off the thermal valve (what ever name) which is on the top hose; I thought it said it would be on the bottom one. I ran a jumper wire across the two terminals and the "floor" setting now has the fan operating. I don't know what this accomplishes other than the valve either has dirty connections or is defective. I will take it to work and see if the heat maintains at the setting rather than drop off to cool yet. If it does the same thing as before, I will probably order my 3d air temp valve (name?) which is above the glove box under the dash cover. It draws air in. The old cars without temp control, the heat setting went straight to the valve on the heater line to open/close the water flow. This one has one end with a tube that goes to the heater motor (I haven't followed it yet) and the other end is open. The third opening goes to an opening above the glove box. I susspect that the air passes over the inside parts, evaluates the temp, and vacuum does the rest. At some point, mine is failing...
:eek:

[87 town]

I would think that the vent would bypass the compressor, but I haven't gotten that far yet.
The car does have the climate control and I have been reading about it. When it is cold out, I have put the control on vent and the heat setting to max heat (85 or so in the red). After a short time, it does put out real GOOD heat, then the fan slows down as normal. BUT then, the air cools and stays cool giving me a fairlyl chilly ride from there. I even opened all the doors when it was 30 degrees and it still puts out only cool air. I am going to try pulling the plug off the thermal sensor on the heater hose in awhile and see if it works better tonite coming home from work. Doing that, from what I have been reading, should make the "floor" setting fan mode work, which at this time does not. Strange.
As far as the ac goes, it was hot when I got the car, August. At first the ac would work fine when set to the left in the blue. The fan slowed down when it approached the set temp. Then suddenly it worked until it got to the set temp, then put out only warm air. Once in a while, the compressor would kick on and cool the car, but then it returned to warm air once it got to the set temp. Right now in Missouri, it is too cool to check the ac out, but I am hoping that when I get the heater fixed, the ac will be part of that system and also function again. The "floor" setting was the same when running the compressor, the fan did not work. I thought that the entire control was bad. I bought a complete assembly from a boneyard the other day because of the dead floor system, but I am reading that that problem is being caused by the thermal switch on the heater hose. I will let you know tomorrow how that came out. I hope I don't break it as it says it is plastic, and those plugs just don't want to come off easily.
I am hoping I don't have a vacuum leak. When you go up a hill the fan slows down and you can hear the system changing doors inside the dash. Again, I hope this is all related.

Regarding the fan slowing down at open excel or going up a hill, for me, in my opion...lol...is not a big deal and the way I see it is that when the car is asking for more power on open throttle it automatically reduces some power elsewhere. There is debate on this issue but it is most recognized when the AC is on and also at WOT at same time. A/c cuts off for a second at that time..
Besides that, and you probably did this already... but check coolant level and I would also consider the thermostat being stuck or needing replacement. May not be any issue at all with your controls,vacumes or sensors. Bad t stat would cause heat to come and go. It is an easy install. You can also test your t stat by removing and running under hot water to see if it is opening and closing properly. But, by the time you did this and need to replace the gasket anyhow, you may as well have bought a new one. A clue on a bad t stat would also be that when cool air is coming out and not hot as you are calling for, your temp gae would also be increasing and the car getting hotter, till it opens and heat comes on again.
Usually on the a/c, at times when mine has not been getting as cold as it should, it has always just been low on freon.

[Tman70]

These 2 might help some...
http://www.lincolnsonline.com/tech/00104.html
http://www.lincolnsonline.com/tech/00130.html

[gadget73]

Sounds to me like the interior temperature sensor (the thing you replaced) is bad. Open the glovebox and push up on the two plastic stops so the door opens all the way. Locate the clear plastic tube that should be visible directly behind the glovebox. Unplug it off the vacuum motor and see if your heat doesn't go to full. According to the shop manual, if there is more than 1/2" of vacuum on that with the temperature set to full hot, then the interior temperature sensor is bad and should be replaced. My car did the same thing your does, hot, to lukewarm, and sometimes by sliding the control to full cold, then back to hot I got heat again. This vacuum motor runs the blend door. There is no water flow control to the heater core, it recieves coolant at all times. Temperature control is a vacuum operated blend door that flips between air from the heater core, or air drawn through the AC evaporator, regardless if its running or not. The fan control for the auto position also runs off this door. When the door is approximately in the middle between "hot" and "cold", then the fan is at its lowest. If it moves one direction or the other based on the temperature selector, it adjusts the fan speed. Engine load will not have an effect on fan speed. If air shifts around going uphill, you have a leak somewhere in the system. Likely candidates are that thermal blower lockout thing (just plug the vacuum hoses) and the coffee can on the fender.

RE the AC compressor: the only positions it runs full time in are the ones marked AC, which are Panel and Hi-Lo. The AC compressor cycles in defrost or mix. Vent is considered an "economy" setting, so you can get hot air, or outside temperature air. The AC compressor will not run.

[RVdually]

I removed the electrical plug on the thermal valve on the heater hose. The "floor" setting worked where it didn't before. The heater seemed to put out heat longer than before. At night, about 40 degrees, I got about 15 miles before the heat went to the cool side again. The coolant level is okay, freeze point to -40, and the temp gauge holds steady at a little under half way.
Two problems so far: The thermo sensor is bad or dirty connectors as the "floor" does not work. By jumping, where does the vacuum go that is going through those tubes?
2) The inside temp valve must be bad, even though it is the second one, both used (1988 and 1992 stamped on them)

I am going to try checking the vacuum motor, check for vacuum leaks, check vacuum valves, and test the interior sensor that several of you guys have mentioned. Thanks. I will keep you informed. (I am getting close to sending this thing to the crusher, or at least trading it off before too long at this rate.)

[87 town]

I removed the electrical plug on the thermal valve on the heater hose. The "floor" setting worked where it didn't before. The heater seemed to put out heat longer than before. At night, about 40 degrees, I got about 15 miles before the heat went to the cool side again. The coolant level is okay, freeze point to -40, and the temp gauge holds steady at a little under half way.
Two problems so far: The thermo sensor is bad or dirty connectors as the "floor" does not work. By jumping, where does the vacuum go that is going through those tubes?
2) The inside temp valve must be bad, even though it is the second one, both used (1988 and 1992 stamped on them)

I am going to try checking the vacuum motor, check for vacuum leaks, check vacuum valves, and test the interior sensor that several of you guys have mentioned. Thanks. I will keep you informed. (I am getting close to sending this thing to the crusher, or at least trading it off before too long at this rate.)

Hang in there. seems like you are getting close. you'll be glad you kept it in the longer run!

[gadget73]

The vacuum portion of that switch opens and closes the outside air door. When the engine is not warmed up, vacuum is passed from the blue tube into the black, closing the door. When it warms up, there is a seal inside that moves and caps off the blue line. The black one loses vacuum and the air door opens. You can actually just eliminate that whole thing by plugging off the two hoses and jumpering the electrical connector. The switch internally burns out because of the high current flow across it. It really should have been run through a relay instead of having the full draw of the blower motor run directly through the switch contacts.

The interior temp sensor I replaced in my car had 1998 stamped on it, and I replaced it in 2005. My car was owned by chain smokers and I doubt that did the sensor any favors. That valve is a temperature sensitive variable vacuum leak. It has a rubber diaphram in it, and a very thin metal plate that warps depending on the temperature. Temperature control is done by increasing or reducing tension on a spring to the middle of the metal plate. If the spring tires, or the rubber gets hard and loses its sealing ability, it stops working. Lower tension makes the metal plate push on the rubber, blocking vacuum to the blend door servo. What usually happens is the rubber gets dry and no longer makes a perfect seal. Vacuum won't release completely on the blend door and you end up with the roving temperature issue.

[RVdually]

I went ahead and replaced the thermal regulator in the heater line. I figured that before going to step two, which is the interior regulator, I should probably do it right. The jumper did work, though.
With the new sensor, the fan starts after a few minutes, just as it is supposed to. It gets pretty warm at the start (set to 80) getting up to 130 degrees (floor setting). After it reaches its set point, it drops to a range of 70 to 90. Does that sound within the range? I think a new one might have a tighter range limit. I will run this awhile and maybe replace it after I get some other problems taken care of. The thermostat runs at 184 degrees and the temp needle doesn't fluctuate at all.
I am going to start working on my high beam problem while I finish testing this out further. Thanks everyone for helping.

[RVdually]

I think I have the heat problem under control now thanks to you guys. I will purchase a new inside temp sensor shortly, which will regulate the up/down temps better.
Right now I notice that upon the least acceleration up a hill (small even) the air shifts to defrost. I'd say from a previous post that I have a vacuum leak and will check it out.
If I remove the line from the "can" on the fender and pump the heat control side with a hand operated vacuum gun, should the vacuum hold steady or does it take a running vacuum to operate the system? Should it be in the off position to hold vacuum, or any position? Thanks in advance

[Red91SiT]

I believe my interior temperature sensor has gone bad, but I'm not sure what this is? and where it is located?

Is this the sensor? right behind the dash? "pictures attached"

[Ivan D.]

Yep, that's the ambient temp sensor, I've been planning on fiddling with the spare one I have to make it work manually, but never sat around to do it.

[gadget73]

Yes, thats the sensor. I would disconnect the line at the vacuum tree and pump vacuum from the engine side of the check valve. If you look at the check valve, it has two thin lines on one side, and a fatter line on the tree. Hook the vac pump to the fatter line. It should hold vacuum in any position, but don't be too surprised if its not completely airtight. I think the shop manual allows for some leakage, but if it doesn't lose vacuum at an alarming rate I would say its probably OK. If it holds 5-10 mins or more, its probably fine. The can itself often rusts at the seams, and the rubber vacuum hose connector on the TBL sometimes has poor fit and leakage problems.