No heat help

[Ariamius]

I am baffled the bpv valve seems to be working but no heat engine running fine at normal temp. new thermostat, radiator cap., is there a fuse for the heater somewhere, no leaks in heater core either. any help would be great..., now the car seems to run a little on the hot side. where should the need on temp gauge be for normal operation?

[cre]

There's a VSV which controls the Heater Control Valve... test it. It's a common failure point.

[Ariamius]

I tested the valve and it doesn't work bypassed from top of solinoid vacuum line to vacuum line from where the switch is and the lever is pulling up now, but still no heat. Truly stumped. removed thermostat and drilled giggle valve out to a 4mm hole. new Radiator cap, and still no heat

[cre]

The jiggle valve isn't going to change whether you get heat or not and its presence isn't going to affect when the thermostat opens. Is the car getting up to normal operating temps in the normal amount of time? Coolant level normal? It may be a blockage in the heater core or a problem with the electrical and air routing system inside the dash.

EDIT: Sorry, I see you said it's running at temp just fine. Normal is dead center, for the most part. If you want to be sure grab the TSRM and measure the reading at the temp sensor directly and use the chart to find the temp it's at.

I'd back-flush the system aggressively.

[dlfred]

I also am having the same trouble. I recently did a HD gasket and when I back flushed the heater core it push out rusty looking water, twice now, Has good flow when doing so. The inside control unit appears to be working, the vacuum operated valve appears to be opening.

Is it possible to have a heater core clogged but still be able to back flush?

[cre]

Sure it's possible. Just because water/detergent is flowing through doesn't mean much of it is. It takes a high amount of pressure to clear out channels which are clogged if water is still able to flow through other routes.

(Before you continue reading all of this though read through the diagnostics posted at the end... might save you a lot of time)
Are you guys using any cleaning/detergent/acid products such as Prestone to clean the system? More caustic solutions will work far more quickly than plain water or citric acid based detergents (Prestone) but need to be thoroughly neutralized after flushing (a final flush with a baking soda solution is all). I've heard from a couple radiator specialists that phosphoric acid is not to be used. Oxalic acid is more effective than citric but less aggressive than muriatic (hydrochloric) acid. Although, I generally don't think it's a good idea to use very caustic cleansers (such as muriatic acid) in a system where a clog may allow the acid to sit in a pocket and keep munching away at good metal... They're excellent for once a year or two year scrubbing of healthy systems. You could try it but be forewarned that if there are any weak spots (a collection of rust particles holding hands) you may finally compromise them. There are solutions available with inhibitors to slow the acid from consuming the good alloys, I recommend you find one and follow the directions closely. As with any coolant cleanser (including the citric acid based ones) it takes time for scale and rust to be dissolved and cleared out... You'll just add it and run it for anything from one day up to a week. Don't expect instant results.

When flushing old systems, flush it until it runs clear; Then, give it another pass with detergent and flush until clear again. Do this until it's pretty much clear right away. In a heavily scaled, blocked and rust filled system this may take quite a while depending on the detergents used and the period they're required to be in the system. Also this wouldn't be a bad time to add a coolant filter, you're going to be freeing up a LOT of shit and it's also just a good thing to have installed. Back flush when flushing on each pass, any large particulate that is freed up is a potential blockage.

If you have the equipment (a 15 to 20psi manometer and a pressure gauge) I'd recommend testing the pressure drop across the heater core. I suspect that a healthy heater core shouldn't see a drop of more than a couple psi but clogged will see a drop of 33% or more... I'm not certain on those figures but that's what I would look for.


Two other things to check are:
http://www.cygnusx1.net/Supra/Librar...aspx?S=AC&P=43
http://www.cygnusx1.net/Supra/Librar...aspx?S=AC&P=37

The air mixture valve in the dash will not open unless the thermistor reports the coolant in the heater core as up to temp.


I hope this helps, it's not exactly my area of expertise.

[interested!]

Originally Posted by cre

Sure it's possible. Just because water/detergent is flowing through doesn't mean much of it is. It takes a high amount of pressure to clear out channels which are clogged if water is still able to flow through other routes.

(Before you continue reading all of this though read through the diagnostics posted at the end... might save you a lot of time)
Are you guys using any cleaning/detergent/acid products such as Prestone to clean the system? More caustic solutions will work far more quickly than plain water or citric acid based detergents (Prestone) but need to be thoroughly neutralized after flushing (a final flush with a baking soda solution is all). I've heard from a couple radiator specialists that phosphoric acid is not to be used. Oxalic acid is more effective than citric but less aggressive than muriatic (hydrochloric) acid. Although, I generally don't think it's a good idea to use very caustic cleansers (such as muriatic acid) in a system where a clog may allow the acid to sit in a pocket and keep munching away at good metal... They're excellent for once a year or two year scrubbing of healthy systems. You could try it but be forewarned that if there are any weak spots (a collection of rust particles holding hands) you may finally compromise them. There are solutions available with inhibitors to slow the acid from consuming the good alloys, I recommend you find one and follow the directions closely. As with any coolant cleanser (including the citric acid based ones) it takes time for scale and rust to be dissolved and cleared out... You'll just add it and run it for anything from one day up to a week. Don't expect instant results.

When flushing old systems, flush it until it runs clear; Then, give it another pass with detergent and flush until clear again. Do this until it's pretty much clear right away. In a heavily scaled, blocked and rust filled system this may take quite a while depending on the detergents used and the period they're required to be in the system. Also this wouldn't be a bad time to add a coolant filter, you're going to be freeing up a LOT of shit and it's also just a good thing to have installed. Back flush when flushing on each pass, any large particulate that is freed up is a potential blockage.

If you have the equipment (a 15 to 20psi manometer and a pressure gauge) I'd recommend testing the pressure drop across the heater core. I suspect that a healthy heater core shouldn't see a drop of more than a couple psi but clogged will see a drop of 33% or more... I'm not certain on those figures but that's what I would look for.


Two other things to check are:
http://www.cygnusx1.net/Supra/Librar...aspx?S=AC&P=43
http://www.cygnusx1.net/Supra/Librar...aspx?S=AC&P=37

The air mixture valve in the dash will not open unless the thermistor reports the coolant in the heater core as up to temp.


I hope this helps, it's not exactly my area of expertise.

Hi! Thanks for your links above, I was having the same problem , : hot heater pipes ,but no heat in the cabin , so, I removed the slider and servo motor from the bottom of its mounting, and moved the door to front/back position and then started the car. Within seconds I was getting heat into the cabin, this must have been the problem , the door was operating in cold air ( air conditioning ) mode and not letting the warm air through .
Questions? : how do I test the servo to operate to open the door to hot air? .
What does the slider on top of the servo motor do?
Many Thanks.
EDIT; my car is a 1987 supra ma70 7mgte auto -registered 1989

[cre]

I can't give you a detailed explanation of every part, I don't have an assembly to look at right now. The servo controls an air mixer; A flap which opens to allow air to flow through the heater core or closes to prevent it from flowing through it to a large degree.... This is how you can have the A/C on and still have coolant running through the heater core. The heater control valve which diverts coolant in the engine bay does open while the A/C is operating, just not when it's on high. So, no heat = blocked heater core, bad coolant valve or bad VSV in the heater control assembly, bad climate control unit, bad thermistor in the heater core, bad servo or stuck mixer.

I'm going off memory here so if I'm slightly off on something it's because I haven't worked on one in quite a while.

Originally Posted by interested!

Questions? : how do I test the servo to operate to open the door to hot air?

See the like I've already posted for diagnostic procedures.

The heater control valve's (HCV aka heater bypass valve) VSV is the most common point of failure.