Beginning July, I had an issue when I drove about for half an hour and the air would only blow hot, the viscous fan would not spin and the left side of the SCV6 engine would shudder, thud and hiss every 30 seconds and the engine idle would drop to 400-500 RPM. This would persist until the air would begin blowing cool again and all symptoms would go away.

This issue has continued to date. Sometimes it occurs while driving, sometimes it happens when stopped for a light, but it does not do it all the time.

I brought it to the main dealer and they insisted all was functioning as designed, despite it's never had the problem before July this year.

As the problem worsened, I brought it back to the main dealer for a metallic taping from the front of the engine as well as the AC issues, again. Their diagnosis was a failed viscous fan, which according to them, would apparently also affect whether the climate control worked properly.

Fan replaced and claimed all was finally in good order.

Started up on the shaded service drive and the air was blowing hot and the newly fitted viscous fan was not running. I left it there running for 15 minutes and nothing changed, engine heated up but no fan, no cold air. Drove about for another 15 minutes with hot air, stopped and engine compartment very hot, viscous fan still not running and all other symptoms present such as shuddering, low RPM, thud, hiss, etc.

Started driving again and air began to blow cold. Stopped, air continued to blow cold, viscous fan was now operational and other symptoms had ceased. I'd made various starts and stops for several more hours and all was good so far, but then again this was no different than the last 3 months.

The next day, hot air again as well as the other symptoms.

Tech said must be the valve on the AC compressor, happens all the time. Had them fit a new compressor and........according to them, still blowing hot air. They intend to continue trying to sort this.

Anyone here have any ideas?

 

So a new A/C compressor has been installed. The only thing, I could think of is a faulty evaporator temp sensor or ventilation A/C condenser is clogged up

 

Yes new compressor. Couldn't be a clogged condenser, remember, other symptoms associated with this concern.

 

The fans are electric? What do you mean by viscous fan?
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The cooling fan, not the blower fan. It's electric but is also referred to as a viscous fan.

Regardless still hot and cold air blowing from AC.

 

Problem may be sorted, at least with hot air only. Main dealer tech found one of the 3 pins in the connector was not completely seated. Was blowing ice cold all yesterday and most of this morning. Too soon to know if the original concern has been resolved.

 

Can you tell us which connector?
Is it the one on the AC compressor?
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It can be confusing that both belt-driven cooling fans AND the newer electric cooling fans have viscous coupling. When someone that hasn't looked at or had to work with electric radiator fans with viscous coupling, viscous = belt driven. My wife has an Oldsmobile with an electric fan that doesn't include a viscous coupler (clutch), but as you described our Jags do.
Oddly my 2012 Land Rover with the same engine as my wife's 2012 Jag uses a belt-driven fan.

 

The harness between the body harness and the compressor harness.