Intake Air Heater Issue

[JWell]

Hi All:



First time on this site altho I've been a member of TDR for three yr or so.



I tried to do a search but really didn't find what I wanted, therefore this post/question.



My brother has a 92 D250 Cummins that does not want to start when the weather is cold. The intake air heater relay(s) click really fast when you turn the key on. The WTS lite comes on, but relays click really fast like a starter solenoid does when when the battery is bad.



Battery is in good shape, I cleaned all the terminals and grounds, replaced one of the relays cause I thought it was bad and the truck started while I was there. The outside temp that day was in the low 50*. (I checked the grid heater too and it seemed to have continuity thru it so I think it's OK and it looks solid just from a visual perspective. )



Saw him a couple days later after the weather had gotten colder (mid 30*) and he said it refused to start and it did the relays did the fast clicking again. Told him I would check on this site to see if I could get some ideas.



I know the IAT Sensor controls how long the heater is to be on based on intake temperature, but would it make the relays do their "tap dance" thing?



Any help or suggestions would be greatly appreciated.



Thanks in advance, Jerry

 

[tugboatphil]

Jerry, you say the battery is in good shape, but not how old it is. I've taken one to almost 7 years once, but 5-6 is normal for my driving and starting. The fact that it runs over on a warm day but not a cold one makes me suspect the battery.

Disclaimer - I'm not an electrician, don't always trust my own electrical work and still think of electricity as "lightning that lives in wall. "

 

[JWell]

This is my brother's truck and I think the battery is only 3-4 yr old. I may not have been clear, but even on a cold day it rolls over great, just doesn't want to start 'cause the air heater doesn't do its' thing with the relays clicking on and off in rapid succession... ... ...



It just seems like something is not holding the relays on when the temp gets down in the 30* and lower.





thanks much for your reply, Phil



Jerry

 

[cerberusiam]

From the description the relays just aren't taking the load when its cold, or, the draw is higher than it should be for some reason.



Could be the grid heater is bad or possibly the conenctions are corroded. I would clean all the connections from grid thru the relays to the battery and see of that helps.

 

[Paul Herioux]

The grid heater on these engines almost never fail, I have only replaced one since I saw my first truck come in the dealership in 1994. The high current relays on the other hand are another story. Before condemning them though, check the voltage at the relay when it is acting up. They should stay engaged down to about 7. 5 volts. The controller does cycle the relays on and off, alternating between the two heaters in the intake which is why you hear the high pitch buzz when they are operating properly.

 

[JWell]

Thanks for the input, guys. I'll recheck all the connections to the relays to be sure everything is clean and tight.



Jerry