In the picture the HAC is the red device and the hose (connected to the bottom port) is what is held. The hose is a large diameter too, so logic would indicate that it connects to a large nipple, but where?
Last edited:
1987 FJ60 High Altitude Compensator (HAC) Routing
- Thread starter BlackPanzer
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
In the picture the HAC is the red device and the hose (connected to the bottom port) is what is held. The hose is a large diameter too, so logic would indicate that it connects to a large nipple, but where?
The hose off the bottom of hac is open to atmosphere.
- Thread starter
- #3
Thanks!
It is always sucking in air at any altitude. At low altitude it's bleeding off vacuum to the manifold to prevent the outer secondary HAC diaphragm on the distributor from actuating.
At altitude, the internal valve inside the HAC valve closes, which allows the carb to suck in extra air (through that bottom hose) and seals off the low altitude vacuum leak... allowing the HAC diaphragm on the distributor to actuate.
Clean the HAC filter. The bottom snaps off of the valve to access it. New filters are still available from Toyota.
At altitude, the internal valve inside the HAC valve closes, which allows the carb to suck in extra air (through that bottom hose) and seals off the low altitude vacuum leak... allowing the HAC diaphragm on the distributor to actuate.
Clean the HAC filter. The bottom snaps off of the valve to access it. New filters are still available from Toyota.
Jumping in here as I’m trying to understand the current state of my HAC and why the idle drops when I cover the atmospheric hose.
Are you able to walk me through the test in this image below, from the Emissions Manual? I don’t follow the air restriction and outflow if the hose is constantly drawing in air.
Thanks
mattressking
10 digits to freedom
The emissions manual pre-test is to determine what position the HAC is to complete the tests.
If vacuum is added to the lower center port (not the bottom-most port) and air is blown into any of the top 3 ports and air escapes from the bottom section, it is in the HIGH altitude position.
If NO air comes out, it is in the LOW altitude position.
If you live in a low altitude/sea level area and it is in the HIGH altitude position, the HAC is most likely faulty. And vice versa if you live in high altitude.
Once you determine the position the HAC is in and it matches your altitude, then continue with testing.
Thank you - that makes sense, but when you say “air escapes from the bottom section”, is this through the bottom most port (normally sucking air) or through the flat bottom of the black cover?
mattressking
10 digits to freedom
From the bottom cover, remove the lower cap with the atmospheric hose and the filter to make it easier to test.
If the HAC system is working, you can easily tell what state it is in (high or low altitude) by just pulling the outer vacuum hose from the distributor advancer while the engine is idling. If you're below about 3800 feet and the RPMs stay the same when the hose is pulled off, the HAC system is in it's low altitude state. If the RPMs drop, the HAC valve is stuck in the high altitude state (not good).
Ok I’ve tested the HAC and it appears to be in low altitude position - where it should be. Thank you for your help.
On to next round of tests.
On to next round of tests.