When the truck was new and thereafter until the a/c system broke, I was able to run the air conditioner with the temperature gage set to hot. I got hot, dry air which was fantastic for taking the humidity out of the truck during our wet winters here in Houston. The a/c system was dormant for about five years until I was able to afford fixing it. But now, all I can get is coolish, warm air at best with the compressor on and the temp switch set to hot. I have ice cold airconditioning, however. My mechanic is stumped. He has been through the duct system and heater system and can find no problem. What can we be missing? Thanks for educated help.
BTW, I use all Toyota parts and the mechanical portion of the truck has been completely rebuilt, except for the driveline. That's next.
yours has been in there 10 years, it may be due for replacement. Ifyou need to run a cold t-stat in the summer, you are just masking someother cooling system problem. Could be a clogged radiator, collapsingradiator hoses, a worn water pump, or even a leaking head gasket, etc. Find and fix that problem, run the proper temp. t-stat and everythingwill work as designed. My temp. gauge never moves, even in 120F desertheat crawling over rocks in a canyon all day long. I did upgrade to a3-row heavy duty radiator about 6 years ago. It solved all my coolingproblems.
That's been rebuilt also, twice. I get heat with the compressor off although its not as hot as it used to be, but it will get hot eventually. I'm not sure about the heater core. I think that was rebuilt. I've spent a chunk of change to peice meal rebuild this old iron. The big reason I do it is it goes where no tractor can go. I love it. But these little quirks are driving me nuts. I never had to rotate the thermostat during its first 10 years. To get it to run cool in the summer time, I have to run a cool stat (I can't remember the temp) and a hot in the winter. Something doesn't make sense.
The heater is purely mechanical, valve on the firewall opens and lets hot coolant through the heater core. You may have some air mixing problems, worn out seals on flapper doors or whatever. Verify the heater core was indeed replaced, try backflushing it anyway. I had all manner of nasty looking junk come out of my '85 heater core when I first black flushed it. Check the thermostat and veryfy it #1 works and #2 is the proper temp. I recall you mentioned you were running a cooler than stock t-stat, but maybe I misunderstood your meaning. I merely suggested that running a cooler than stock t-stat to keep the engine cool is just masking an underlying problem. I run the factory spec. t-stat in my '85 and get loads of heat out of the heater. When my A/C used to work, I got loads of dehumidifying with it running. Go through the electical stuff a component at a time, identify the part, what it does, what it connects to and then verify it works properly.
I run the SAME t-stat year round from the winter cold in the Sierra Nevada to the summer heat in the deserts of sothern California. I never change t-stats to match the season. Why do you *need* to run a cold t-stat in the summer? If your engine and cooling system are functioning properly, there is no need to do that. If you have to swap in a colder t-stat to keep it cool in the summer, you are just masking some underlying overheating problem. Have you actually tested the t-stat you have in there to see if its working or not? Pull it, drop it in a pan of hot water on the stove with the thermometer and observe where it opens. I once ran one of those fail-safe t-stats (MotoRad) and had the fan clutch fail, letting the engine get a bit hot, the t-stat opened full and latched that way (that's the fail safe part). Well, later that fall when it cooled off, I noticed a distinct lack of heater output. Pulled the t-stat and sure enough, it was wide open. Put in a new OEM and it worked fine. I now run the superior 2-valve t-stat, it maintains a much tighter control on engine temps.
I guess I didn't make myself really clear. The truck is a 1984, which I bought new in 1984. Around 94, when I didn't have any money the a/c quit and it sat dormant for about five years. Starting in 97 I blew the head gasket, which has led to a section by section rebuild. The engine has been completely rebuilt, top to bottom. The cooling system has been completely rebuilt. I've had a variety of electrical issues addressed, some very odd. We've had the duct system all apart and the cooling system dismantled, recored, flushed back and forth and a whole slew of thermostats installed trying to find the right temperature. I've had the brakes rebuilt twice, we won't go there right now. I'm losing my confidence in Toyota parts and Toyota Parts people knowing a damn thing. The a/c dash switch has been replaced, everything lubricated and all the baffles move back and forth. The water pump has been replaced and again flushed back and forth.
One thing, because it is an 84 model, there are discrepancies in the Toyota shop manual and all mechanics manuals. The wiring trunk is not all colored the way the manual says and relays and logic switches are not all where they are supposed to be. I am not really wanting to tear my cab apart again trying to find this gremlin unless somebody can give me some ideas outside of the normal repair ideas. I'm 90% sure that the heater core was replaced, but I need to check my records. Could there be an electrical sensor that is causing this problem. My mechanic just chased down a problem with a logic switch for the a/c which was switching the a/c off randomly. It did nothing for the heating issue that I'm looking for. My experience is that the idiot gauge for heat rides just below the mid point. At some point in my repair history, a larger radiator than stock was installed, so it runs a lot cooler than designed. However, the a/c worked properly at that time, also.
The result is the heater gets hot, the a/c gets cold, but I can't get the humidity out of the cab on cold, wet nights/days without running the a/c on freezing cold. If I push the temp switch all the way to hot with the compressor on, the temperature in the cab is comfortable only if I wear a coat and gloves. This why I am asking this intelligent group of Toyota owners if there is anything we could have missed. Thanks
It hadn't been rotated (hot to cold) in the first ten (actually more) years. It has been replaced regularly.
I read your article on your thermostat relacement. I have a 22r with the by-pass hose. I had always wondered at the need for the by-pass. I'm not certain how having a 2 stage stat with a working by-pass would be an advantage to me. Mine also runs cold when the stat is removed. It hardly ever heats up. basically what I've had to do is "rotate" a thermostat in during the winter that forces the truck to run hotter to get adequate heat and a different stat in during the summer that allows it to run cool. I know this isn't right. The only thing I can think of is the larger radiator causing a problem of allowing adequate heat to form to operate the heater.
The only other thing you might look at is the A/C temp. sensor (thermistor) that I think is used to control the temperature of the conditioned air. Maybe its out of whack and putting the A/C into full cold mode. When in defrost mode, you should normally get very little A/C compressor operation if its cold. I used to run an indicator light that would come on when the A/C ran and you could see if was mostly off when in defrost, maybe 20-30 seconds off and then a few seconds on.
I don't WANT to run two stats. I WANT everything to run right. Well the first thing I will do is test the stat and check its type. But I don't think that is the problem because we have been through all the ranges of Toyota stats, except for the 2 stage. We haven't replaced or cleaned the core. It has only been flushed and reverse flushed, twice in the last 12 months. can a core be rebuilt like a radiator or is it cheaper to replace it? I agree that there must be another underlying problem, but after doing all the obvious things, I feel kind of stumped.
I'm not saying to run two t-stats, just run one that is the proper temperature, summer, fall, winter, spring. I'm just asking why you run a cooler t-stat in the first place? If everything is working right, as Toyota designed it, one t-stat is all that is needed. I only run one t-stat, 190F, it works fine in the winter cold in the mountains and it works fine in the desert heat.
Usually cheaper to replace both radiator and heater core. I just went through that a year or two ago on my other vehicle, a new radiator was about $120, re-coring my old radiator was $220. I opted for the re-core as it ended up with a better fitting unit and being the old one was brass/copper, it could be rebuilt in the future, unlike the less expensive plastic/aluminum unit.
Thanks. How do you test the thermistor? Is there a method to tell if it is operating correctly? I am wanting to move on to the chassis part of my truck, but I want this stuff to work first.
BTW, I have been looking at your site. There's a lot of info there. Are you a mechanic or something pertaining to trucks?
I just replaced my Master Cylinder for the second time in eleven months. I was interested in your explanation of the proportional valve. I always wodered why this truck has such excellent stopping qualities even with no load in the bed. Do you think this valve can feed back pressure to the master cylinder if the valve senses different pressures from left and right rear wheels? My drivers side rear seal broke and lubricated the drum which didn't wear as much as the passenger side. For some unknown reason the master cylinder failed. This failure doesn't make sense to me.
The Factory Servie Manual would contain that information:
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any competent auto A/C shop should be able to do that test.
Nope, just learned from the FSM and eperience owning and working on Toyota trucks over the years.
No feedback back->front. There is a front->back feedback, in that if you lose front braking pressure, the LSPV-BV is overridden, giving full brake presure to the rear brakes (that's the BV part - Bypass Valve). I think my '85 still has the OEM brake master cylinder in it, clutch m/c leaked about 5 years ago and was replaced with a new OEM unit. I do plan on replacing the brake m/c with an upgraded FJ-80 unit to give me more fluid volume to work better with my upgraded front brakes and soon to be rear discs.
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