Will heater work without anti dieseling relay?

[NotaBronco]

Don't have the relay in my truck and don't plan on running the a/c anyways, but could definatlet use the heat. Will the heater still work without plugging in the relay? If not, does anybody know a way to bypass it to get my heater running? Thanks!

[Acorn]

I believe your low and med will work. But I'm having a brain fart right now. See if this helps. http://67-72chevytrucks.com/vboard/s...d.php?t=675589

[Davidf]

I believe all fan speeds will work without the anti-dieseling relay. Mine is not connected and all,fan speeds work. I purchased a new anti-dieseling relay connected it and it did not work plus killed high speed relay. Anyone care to guess why?

[davepl]

AC trucks need the relay on the heater box to fire the heater motor to full 12V on high. There may be a separate anti-diseleing relay at the carb, and that would not affect heater output at all, and probably could be missing without effect.

So, no anti-dieseling relay, but you do need the other one if it it was an AC truck for the fan to work on HI

[Davidf]

Dave, anti-dieseling relay is in the cab mounted to lower lip of dash next to a/c control panel. There is, of course, a separate fan high speed relay mounted on the Evap box, right side, behind glove box.

[davepl]

Originally Posted by Davidf

Dave, anti-dieseling relay is in the cab mounted to lower lip of dash next to a/c control panel. There is, of course, a separate fan high speed relay mounted on the Evap box, right side, behind glove box.

Mine's either long gone or it wasn't used on the '70.

So the relay is under the dash, triggered by the (heater control?), and it controls a little servo or plunger or solenoid at the throttle to 'relax' the throttle when the engine turns off? Sort of an electronic high idle, but reversed?

I think the HI fan is triggered by the AC controls as well - so I can't say with any confidence that they did or didn't combine them into a single circuit, other than you don't always have the fan on HI for AC, so they are somewhat different. Wonder why they didn't just tie it into the AC clutch, which is where the workload comes from anyway?

I hope they're separate for your sake, then you don't need it.