Another little issue that popped up during our drive back from Byron, NY to Las Vegas, NV — our dash AC stopped working! Which, was unfortunate, since it died as we were dropping down through Utah and into Nevada – in August.

I’d been noticing an oddity for a while, where the fan clutch for the engine fan would kick in/out several times over a few seconds before it would finally fully engage. I had up until the fan drive gear box failure -thought- that it was indeed, somehow the fault of the fan drive gear box itself, since it had been leaking it’s gear oil for quite some time.

Once the gear box failed, and was replaced, then rebuilt — I was surprised that the fan clutch continued this odd behavior. There are two items which cause the two-speed fan clutch to kick into ‘high’ mode:

  • Engine temperature going above a certain set-point
  • The dash AC being on
    • This causes the fan clutch to kick into ‘high’ mode for 20’ish seconds for every minute ( don’t quote this, I’m running from memory )

Through some diagnostics, I determined that this multi-engagement cycle was related only to the dash AC being on, so it had to be something with the dash AC control circuits. I started looking at the compressor clutch, and noted that it too was not engaging reliably, and would often follow the fan clutch in unison.

That is, up until both items stopped engaging entirely.

We made it into Las Vegas and I had scheduled an appointment at the NIRVC service center in North Las Vegas. My suspicion was something to do with the high side or low side pressure switch on the AC coolant loop. This was the most common cause of such issues based on my internet searches, and replacing either of those pressure switches required evacuating and re-filling the AC coolant — a task I didn’t have the tools for ( the vacuum pump specifically ).

A day before my appointment, I thought it might be nice to know where those limit switches are so I could help point the NIRVC tech to the right area. I’d searched for them in all visible locations and had come up empty. So I called the Tiffin Service line and asked for the chassis team.

I had a great chat with the chassis team. After hearing my problem description, they lead me through a series of checks, advising that the high / low pressure switches were unlikely to be the culprit. And, they were right! Instead, they helped me chase the issue to a failing relay – under the dash.

There are two of the same relay in that area. The one on the left is used to power the ‘high’ speed dash fan. The one on the right controls the AC compressor / fan clutch engagement. Since my ‘high’ speed dash fan was working well, I swapped the two relays. And voila! The dash AC kicked in, fan clutch kicked in, and I was producing copious cold air! And guess what didn’t work now – my ‘high’ speed dash fan. 🙂

I left the relays in their swapped config until I could get a replacement since the ‘high’ dash fan relay was accessible through the dash drawer, but the AC / fan clutch relay was buried a bit further in. I was able to find a drop-in replacement for the relay at NAPA auto parts (and now carry a spare, just in case).


Resident Tesla nut and polymath. Raised in eastern Kentucky, joined the US Navy at 19 to operate a Nuclear Reactor on a Fast-Attack submarine. After finishing his enlistment, Michael has continued to follow his passions in technology, astronomy, and of course, traveling the country.

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