1991 Toyota truck heater problem

I just bought a '91 toyota pickup and I've discovered that the heater doesn't work. The guy I bought it from told me that there's a problem with the
blower...he said it needed a new heater fan resister, I think? The blower works, but only on high, otherwise it stays off. Besides that, it only blows cold air. I've located the heater core and I'm certain that I can change it myself if that's what's needed, but I think that it may just be the thermostat....So basically there's two problems: 1) The blower isn't functioning properly. What do I need to fix it? 2) No hot air comes out when the heater is turned on. Thermostat problem or heater core, and how can I tell which one it is?
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It needs a ballast resistor.
The resistor pack is open in all speed settings except High. It is a common part that should be available at the parts store down on the corner.
Blowing cold is a sign that the coolant is not circulating through the heater. Either the plumbing is clogged or the water pump impeller is worn out. If the impeller is worn, you should also notice that the truck (engine) gets hot while stopped in traffic, then cools again when the truck gets going. My money is on clogged plumbing.
You can clear the plumbing by disconnecting the heater hoses and connecting a garden hose to one and turning the hose on. This will flush clear water through the heater core and hoses. You could, and probably should, flush the entire cooling system.

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It doesn't use one.

The blower resistor is not used for high speed.

If the water pump were bad the truck would overheat.

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Ballast resistor is the functioinal equivelent to the blower resistor.

That's correct. The resistor(s) is(are) used for all of the other speeds except high. This is why the other speeds fail and high remains working.

True, mostly.
There are reports of failed impellers that let the engine maintain mostly normal temps, but the temps rise when airflow slows. This symptom is also common when the fan clutch fails, but we are not talking about the fan clutch so I did not mention it earlier because I did not want to get the OP side tracked. We are not talking about the fan clutch because it will not affect the heater performance ...
I agree that there would be other symptoms of a worn impeller, heat being the most significant. But, the impeller can fail where coolant flow through the heater core is diminished, while flow through the motor is marginable. If this was the case, temp problems in the motor should crop up soon, if they are not apparent already. This is why I put my money on the clogged plumbing to the heater core, or a clogged core itself. My remedy for clogged plumbing and/or core is to flush with a garden hose. It would be better to take the truck for a professional flushing because they will properly capture the coolant that comes out,
You should have read all of my first post, then I would not have had to explain this all again.
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Blower motor resister is bad. The reason the blower motors works on high speed is that the resister is not used for full speed.
Do you have an engine temp gauge on the dash ? If so, the pointer should be in the middle of the scale when warmed up, if the thermostat is working correctly. If the gauge reads lower or stays around the cold mark your thermostat is stuck open or the wrong temp for the truck.
You could also have a plugged heater core. With the engine warmed up open the hood and feel the hoses going to the heater core. Both hoses should be hot, which would indicate coolant flow. If the hoses were cold it would indicate no flow. I believe you also have a hot water valve in one of the hoses that is worked by a cable. Makes sure the cable is connected and that it moves when you slide the temp control from hot to cold. If you have little to no flow in the heater core you may be able to remove both hoses and flush it with a garden hose.
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Thanks guys! That answers one question, but I still have a problem...
I do have an engine temp gauge, and it reads really really cold, so it seems like there must be a problem with the thermostat, which is what I suspected. However, neither of the hoses from the heater core is hot, so it seems like the heater core is also plugged. Tomorrow I shall undertake installing a new thermostat and flushing the heater core. Oh, and the hot water control valve is connected and moves when the temp control slides from hot to cold...one thing I don't have to fix, yay!
As for the blower, I just replaced the fuses and the relay, but the blower is still only working on high. The relay had condensation in it, as did the fuse area, and both the fuses and relay were corroded. I cleaned everything out as best I could...is there something wrong with the area the relay plugs in to? There didn't seem to be any obvious corrosion anywhere else other than the fuses and relay themselves....Any other ideas?
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You still need the resistor pack. If the fuse was the problem, the fan would not work at all.
If the truck indicates that the engine is cold, AND the engine really is cold, then the heater is not going to blow warm. It follows that you have a t-stat that is either missing or is stuck open. Either of these conditions will cause the temp guage to indicate cold AND the engine to actually be cold. Top this with cold temps where you live (Snow Belt, for example) and the engine can be being harmed by the lack of warmth.
ONE MORE TEST Find out if the heater is TRYING to blow hot. Select the Vent setting, and Max heat, and feel if the air is warm or not. If warm, AND you live in the snow belt, then the heater is trying to work, but the stuck/missing t-stat is not allowing the heat to rise to a level sufficient to warm the motor or the cabin. (For this test to work, you need to let the motor run for several minutes -- the heater in my truck stays on cold for almost the first 2 miles in the morning, you should see if the heater blows warm after at least 3 miles.
What is the outside temp when you notice the temp guage stays on Cold?
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Yes! Definitely the resistor pack. Two of the coils are broken and the ceramic running along all of them are broken and missing.

The heater does nothing but blow really cold air directly into the cab. I live in Northern California, below snow level but certainly cold. The outside air temp has ranged between the 50's up to low 70's when I've been driving. It does seem that the truck's temp gauge registers colder when it's colder, but it hasn't gotten into a normal operating range since I bought it. Right now it's 46 degrees, I drove the truck earlier today and just had it warmed up in the driveway for over 5 minutes, but to no avail; the air blowing into the cab is the same temp as the air outside....
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When you replace the resistor, keep an eye on the heater blower motor function itself. If the motor is flaky because of worn brushes or bad bearings it'll start fine then quit after running a while.
The combination of locked-rotor current from the stalled motor and no cooling fan airflow blowing over the coils of the resistor pack will quickly burn up the new resistor pack. A very expensive way to stop the motor current.

Thermostat failed open, or missing.
Get the new t-stat at the dealer - there are minor visible differences between the aftermarket ones that make major operational differences if you use the wrong unit... And they can be installed backwards, so read the Service Manual.
Note that sometimes people remove the t-stat to "fix" (mask) another problem like a badly clogged radiator or an eroded water pump. Don't be too surprised if you fix one problem and find another.
--<< Bruce >>--
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Thanks Bruce...now just a few more q's.... :)

Should I just open up the motor and check it while I'm under here? Seems like a pain in the butt, but better now than a thousand miles down the road and having to get at everything again anyway. Besides, it seems like finding a resistor pack is going to be near impossible...I've already gone to both wrecking yards in my little town, and all the packs we found were already broken, so I definitely don't want to burn up the new one, when I finally find it. Anybody know of a place to look on-line?
Thanks for the tip about the t-stat....I was just going to go to Napa, but I guess I'll head to the dealer after all.

The radiator was replaced a couple of years ago, but peering inside it looks like I need to get the whole coolant system flushed instead of just the heater core like I was planning, so I guess I'll drive her in to the professionals for that so they can deal with the coolant...although it doesn't seem like the proper ratio of water and coolant was used, as there isn't a really pungent coolant smell when the radiator cap is open. How would I know if the water pump is eroded?
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You can get the resistor pack through www.rockauto.com, I believe they carry them by several manufacturers.
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Awesome! They do have them, and for cheaper than elsewhere. Thanks!
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You would have overheating problems.
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On Tue, 26 Feb 2008 23:23:01 GMT, "LucifinaMae via CarKB.com"

Rank that as "Royal Pain", because once you check or change the brushes and clean & grease the bearings, you have to get the case together and closed again.
They usually have an obvious trick for keeping the brushes retracted as you put it back together (if you know to look for it), usually involving a strategically placed hole and a length of music wire - or a straightened out paperclip - to hold or "cage" the brushes in the retracted position as you slide the case halves back together. Once it's together you pull the wire and that releases the brushes.

The heater blower resistor is probably going to be a Dealer Only item, search around for dealers with an online presence that will discount them. As you've found, they are too popular at junkyards.
Don't worry /too/ much about killing the new one - just be aware and alert that the motor can stop when it shouldn't, and kill the heater power fast if/when you notice it has stopped.

I just change the pump on mileage if it hasn't failed of natural causes (seal and/or bearing) by 120K miles.
On cars with a timing belt, or worse where the timing belt drives the water pump, change the pump every time you change the timing belt. It should go every other, but since you are already right there to do the timing belt that's not the way to bet.
--<< Bruce >>--
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Bruce L. Bergman wrote:

The dealer is not the only option. Kragen, Autozone, and NAPA all have listings for Toyota heater blower motor resistor packs.
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| I just bought a '91 toyota pickup and I've discovered that the heater doesn't | work. The guy I bought it from told me that there's a problem with the | blower...he said it needed a new heater fan resister, I think? The blower | works, but only on high, otherwise it stays off. Besides that, it only blows | cold air. I've located the heater core and I'm certain that I can change it | myself if that's what's needed, but I think that it may just be the | thermostat....So basically there's two problems: | 1) The blower isn't functioning properly. What do I need to fix it? | 2) No hot air comes out when the heater is turned on. Thermostat problem or | heater core, and how can I tell which one it is? |
After reading all of the posts I agree with Bruce Bergman's post, but would like to add that the heater valve could be a problem too. I had that problem with an '87 that I bought some years ago. But, you wont know until you get the engine up to temperature and still don't have heat. Unless, you take the hose lose from the heater valve and the other side of the heater and flush water through it.
--
Anyolmouse

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