Community Forums

KroepelXL · 03-15-2016, 11:58 PM

Just picked up a 2006 Mandalay Presidio 39C equipped with a WorkHorse Chassis, ISC 330, Allison 3000, 47000 miles.

If the chassis air conditioning is on everything works perfectly while driving...climbing a grade, cruising on flats at 70mph, or just putting around town.

When I turn off the chassis (or dash) air conditioning the dash temp fluctuates between the middle of the gauge and almost to the "Hot" line. It goes up and down very quickly...probably from the middle line and up almost to the top line and back down to the middle all within a minute or two.

The previous owner installed a secondary temp gauge with numbers on it and it shows 180 for as long as I drive with the AC on. As soon as I turn it off, or to vent, or to defrost, or to anything else, the engine temp slowly creeps up on the stand alone gauge, and the dash temp gauge starts going up and down very quickly.

If I have the AC off for a while and the temp gauge is doing its up and down thing for a good while, as soon as I turn the AC back on it blows SUPER HOT AIR for about five minutes.

I know it sounds crazy, or at least I think it does, but does anybody have any idea what this could be? Are some lines crossed or something?

Thanks!!!

Mr_D · 03-16-2016, 12:17 AM

Usually turning on the air con sets the cooling fan to run at high all the time. Turning the air off lets the fan changes speeds, runs on low, then as the temp rises it goes into high speed.

KroepelXL · 03-16-2016, 08:43 AM

So it seems like the AC system and the motor cooling system shouldn't interconnected at all. Is that correct?

How do I make it so the fan remains on the high full-time? And by doing that, am I rubbing some horsepower?

Skip426 · 03-16-2016, 09:32 AM

Welcome to iRV2.

Workhorse chassis with a diesel ? I may be wrong but I thought they were all gassers.

The rad fan controller; or it's sensors; may be your issue, as Mr_D says , with the A/C on the rad fan might run on high and with your temp under control, it probably is ; and yes that robs power and mileage.
Because the A/C condenser is in the rad fans air flow , along with the CAC, the fan speed is stepped up to high for proper A/C operation. Some coaches the fan runs high all the time with the A/C on , others will cycle the fan only when the A/C compressor is actually working , which is about 1/2 the time the A/C is on.
When you have been running with the A/C off , there will he hot coolant circulating through the heater core, when you switch the A/C on , a control in the heater hoses "should" shut off the water flow and then the A/C evaporator begins cooling the air box in the dash and then starts to cool the interior. This takes time ; but 5 mins sounds excessive.
Your coach may, or may not be equipped with the auto shut off of coolant flow to the heater core, many owners have installed a manual water valve to aid A/C operation.