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The HAI flapper (Air Control Valve) in the intake is stuck in "engaged" mode -- i.e., it only draws hot air from the hot-air riser, and never relaxes so that it will draw cold air from the front. The flapper itself is not stuck. If I disconnect the vacuum line from the HAI diaphragm, the flapper snaps into "normal" position. The problem is, even when the engine is at full normal operating temperature, there is still a vacuum on the line and that actuates the HAI diaphragm, which holds the flapper engaged.
Seems to me the likely possibility is that the Thermo Valve is not actuating when the temperature rises. Is there a way to test the Thermo Valve?
It can't much be the vacuum because the vacuum IS working -- to a fault! Could it be something else? The Air Control Valve remains in this position regardless of engine temperature.
I have to agree with you that the Thermo Valve is not actuating as it should. The Automatic Hot Air Intake system is pretty simple in that it only has a few components: a vacuum supply, a Thermo Valve, a Diaphragm, and an Air Control Valve.
Since you have proven that the diaphragm and Air Control Valve is working on its own (moves up when vacuum is applied on the diaphragm and down when there is no vacuum on the diaphragm) and you have a good vacuum supply, by process of elimination the only component left is the Thermo Valve.
The only real test for the Thermo Valve is that you have vacuum at the diaphragm when the Air Cleaner temperature is below 30°C (86°F) and that vacuum is no longer being applied to the diaphragm when the Air Cleaner temperature is above 45°C (113°F).
There is not much information in my 1987 Factory Repair Manual on this system, but here is what they have:
Makes sense. I pulled my thermo valve out. Cooled it off with a stream of air. No change. Heated it with a blow dryer. No change. I would say it is shot. I was able to find a couple of used ones. Will try them out. There is no telling how long it has been defective! Gotta wonder what else in the infamous 22R Byzantine vacuum system is not working as it should!
If you have any thoughts on high-failure things I should check for, please let me know.
I got another thermo valve today. It needed a good cleaning, and had to be unplugged, but once air started moving through it, it functioned properly. Calibrating it now is a little tricky, but I don't think it matters a whole lot precisely where it switches. I know when the truck starts up in an ambient temperature of 70 degrees, it is drawing hot air, and after the engine warms up, it starts drawing cool air.
No telling how long my valve was shot and it was only ever drawing hot air.
01-04-2019, 07:14 AM
