Sunday, February 16, 2020

Day 11 - Grid Heater

This is the ground side of the grid heater on the bottom of the intake manifold. The grid heater is an electric heating element inside the intake manifold that is used to preheat the air before enters the engine. It is used when the engine is cold. It is supposed to continue cycling after the engine starts. There is a relay that is controlled by the engine computer to operate the heater. I initially checked to make sure there was 12vdc on one side of the relay. From the other side of the relay to ground, there should have been a very small resistance from the heating element. But it was an open circuit which either meant the element failed or the element ground was broken. Closer inspection of the ground side showed a short ground strap that ran from a bolt and back to the same bolt instead of to the ground bus bar. When I measured the resistance from the relay to the bus bar, it measured very low but non-zero resistance so the element was good!

You can see the ground strap in the second picture. Sometime, someone worked on the engine and forgot to reinstall the ground strap. So, for as long as we’ve owned this coach, the grid heater was non-functional. No wonder it’s been so hard to start when cold. I couldn’t get to the bolt with the ground strap without removing part of the intake manifold so I picked up a battery cable from ACE and ran another ground from the bus bar to the engine block. Now, when measuring resistance, I get about 0.3 ohms. This is pretty approximate as it’s near the limit of the meter but that is about 50 amps when energized. (E/R=I Ohms Law) When the “Wait to Start” light is lit, the battery voltage slowly drops as it should. It still smoked when started but it did start without the block heater. But Bridget pointed out that it wasn’t that cold.

We’ll see if this fix does anything. In the meantime, I’ll enjoy my new rocking chair from Camping World while watching a 45’ class A trying to fit into the spot next to us. Interesting watching them as the wheels on the tag axle steer. Kinda cool! I didn’t know they did that.

I had thought that we may need propane before checkout tomorrow but tonight’s low temperature is forecast to be 55°F so the heat pump should be fine. We are down to ⅛.