HVAC Controller problems, please help

[MKIII_for_sale]

Ok...here's the skinny.


I was given a 1990 MKIII with the 1G-GTEU and automatic. I am trying to sell it over here, but unfortunately, there are a couple of problems I need to fix before I sell it. I have this problem with selling a car that doesn't have all components working properly.


The problem.

The HVAC controller seems not to be working. It blows cold air no problem, but when you move the slider to heat, nothing changes, so it blows cold air 24/7. On my other car, when you slide the the tap, you can hear something behind the dash move...like a motor or something, but not with the MKIII. The heater core is in good shape, I inspected it thinking it might be the problem. I talked to a local tuner shop that I am in good with and they said I may have to take it to a dealer, which I do not want to do.

Is there a fuse or a relay somewhere I can check or do I have to pull the controller out and check for loose connections somewhere. If that is the case...how do I pull the counsel assembly apart to get to it?

Thanks for any and all help you all can provide. I need to get rid of this car ASAP as it is parked illegally behind my father in laws house.

-Neal

 

[JMDigital]

Slider? I have an 89 but I thought the heater was done with a temp gague not a slider? Can you take a pic of what you mean by slider? There are a few Heater threads going on right now.

 

[Facime]

most likely your heater vsv is bad. Its on the firewall on the passenger side just above the charcoal canister. you can try bypassing the switch by plugging the vacuum source right into the diaphram and see if the diaphram operates.

I had to do this on my 89t

 

[Dirgle]

Not trying to propagate mis-information here, so correct me if I'm wrong please. But I believe the GA-70 came standard with a manual climate control, not digital like the ones we see in the MA70s over here.

If that's the case I'm still not sure if it's still electrically controlled, vacuum controlled, or controlled via cable. Until we know that it would be hard to trouble shoot.

 

[Facime]

The heater VSV controls the flow of hot water to the heater core. Its Toyotas way of trying to make the A/C system more effective. When you have the heat slider to cold the valve is closed and therefore no hot water is going to the core. When you slide the heat to hot, a switch located under the VSV tells the vacuum line to feed vacuum to the diaphram, thus opening the valve and allowing hot coolant to circulate through the heater core. Either the switch is bad or the diaphram is bad or I suppose the vavle could be gummed up.

On a RHD I believe this located on the left side of the firewall in the engine compartment. Either way, its the first thing to check when diagnosing a "no heater" situation.

 

[MKIII_for_sale]

most likely your heater vsv is bad. Its on the firewall on the passenger side just above the charcoal canister. you can try bypassing the switch by plugging the vacuum source right into the diaphram and see if the diaphram operates.

I had to do this on my 89t

Hey thanks. When you to plug the vaccum source into the diaphram, what diaphram are you talking about. Do you have a pic of that by any chance, or could you link me to another thread that might have a pic of it?

-Neal

 

[Facime]

In that pic right there, mounted on the firewall just above the charcoal canister, the round metal looking thing, with the big wire loom running behind it. That the heater vsv. The vacuum line running to the switch right below it...run it to the top of the diaphram instead (you can see the vac line going into the diaphram in that pic)

 

[MKIII_for_sale]

Thanks a bunch for that picture man. Now, when I run that other line to the top of the diaphram, will this cause the heater to be always on, or will the slider now be able to control the valve?

 

[Facime]

Thanks a bunch for that picture man. Now, when I run that other line to the top of the diaphram, will this cause the heater to be always on, or will the slider now be able to control the valve?

The slider doesnt control the valve, but you can still chose cold or hot output, it mixes it with outside air just like it always had.