Warm dash A/C

Covers engines and transmissions
chuckster
Posts: 109
Joined: Thu Aug 27, 2020 4:53 pm
Location: Meridian, ID

Warm dash A/C

Post by chuckster »

Hi All,

My dash A/C blows fairly cold air when sitting still/idling but when I start to roll at speeds it gets very warm. Anyone experienced this same issue or have some ideas what may be causing it? Where would warm/hot air be introduced?

Happy trails,
Chuck in Meridian, ID
'01 Safari Zanzibar 3646 (side entry)
Cat 3126B / Allison MD3060
Magnum M-Series "Blue Max" chassis
Owner since 8/2020

wolfe10
Posts: 93
Joined: Sun Oct 27, 2019 4:12 pm

Re: Warm dash A/C

Post by wolfe10 »

If water flow to the heater core occurs (valve not fully closed) it will introduce HEAT.

Faster engine speed, more coolant water flow to the heater core.

If ambient temperature extremely hot, while moving, more outside air can come in if recirculate door not completely closed.
Brett and Dianne Wolfe
Ex: 2003 Alpine 38'. Ex 1997 Safari Sahara. Ex 1993 Foretravel U240
Moderator, FMCA Forums 2009-2020
Chairman, FMCA Technical Advisory Committee 2011- 2020
Moderator, http://www.dieselrvclub.org/ (FMCA chapter) 2002-

TDJohn
Posts: 246
Joined: Sun Oct 27, 2019 11:34 pm

Re: Warm dash A/C

Post by TDJohn »

To add to what Brett has said, if the temp sensor goes bad, it can cause the coil to ice over, restricting air circulation and not allowing what air that does pass through to cool off. Also, these coaches have a lot of air infiltration leaks up front, so when going down the road, a lot of hot air can infiltrate into the cabin, overwhelming the a/c output capacity.
John
'95 Serengeti, Cummins C8.3-300
Allison 6spd.

chuckster
Posts: 109
Joined: Thu Aug 27, 2020 4:53 pm
Location: Meridian, ID

Re: Warm dash A/C

Post by chuckster »

wolfe10 wrote:
Mon Apr 26, 2021 10:53 am
If water flow to the heater core occurs (valve not fully closed) it will introduce HEAT.

Faster engine speed, more coolant water flow to the heater core.

If ambient temperature extremely hot, while moving, more outside air can come in if recirculate door not completely closed.
The ambient temp outside the coach was relatively cool as it was still morning. Where is the recirculate door located in the ‘01 Zanzibar 3646? Is it up front in the area just behind the headlights?

Thanks,
Chuck in Meridian, ID
'01 Safari Zanzibar 3646 (side entry)
Cat 3126B / Allison MD3060
Magnum M-Series "Blue Max" chassis
Owner since 8/2020

chuckster
Posts: 109
Joined: Thu Aug 27, 2020 4:53 pm
Location: Meridian, ID

Re: Warm dash A/C

Post by chuckster »

TDJohn wrote:
Mon Apr 26, 2021 1:01 pm
To add to what Brett has said, if the temp sensor goes bad, it can cause the coil to ice over, restricting air circulation and not allowing what air that does pass through to cool off. Also, these coaches have a lot of air infiltration leaks up front, so when going down the road, a lot of hot air can infiltrate into the cabin, overwhelming the a/c output capacity.
John,
I don’t think the coach had time to have the coil ice over. I start the coach, turn on the A/C and it is cold. Turn off and then 5 minutes later I am on the freeway and turn the A/C back on to test and warm air is flowing through the dash vents.

Thanks,
Chuck in Meridian, ID
'01 Safari Zanzibar 3646 (side entry)
Cat 3126B / Allison MD3060
Magnum M-Series "Blue Max" chassis
Owner since 8/2020

TDJohn
Posts: 246
Joined: Sun Oct 27, 2019 11:34 pm

Re: Warm dash A/C

Post by TDJohn »

Then as Brett said, your heater control valve is not closing for what ever reason. If it is cable operated like on the older coaches, it could be the cable binding and not letting the valve close, as the engine warms up under the load of driving the heater core starts pushing out the heat. You could temporarily disconnect the heater core or pinch off the heater core hose and see if the problem still exists.
John
'95 Serengeti, Cummins C8.3-300
Allison 6spd.

Ozium
Posts: 3
Joined: Tue Nov 17, 2020 12:45 am

Re: Warm dash A/C

Post by Ozium »

Without any gauges this is what I would do;

Take a digital thermometer and put it in the vent closes to the evaporator, close the other vents and turn the fan on low
Start the unit and turn the ac on in recirculating mode and turn the temp dial to the coldest and then go back and see if the ac comp is engaging.
If it cycling on and off then your refrigerant is low and you have a small leak.
If after a minute the ac clutch stays engaged then go back to the front and check the outlet temp.
Now go outside and check to make sure the condenser fan is working.
If the fan is not working the ac will run for awhile then the hi-pressure sensor will turn the compressor off.
Now go back and inside and check the outlet temp again, if it’s staying around 10-20c 50-70f then the water valve for the heater core is probably leaking/cable seized/loose cable clamp screw.
If everything is working good you should see the temperature cycle between 3-7c 34-48f
If the temp drops below freezing then the t-stat sensor is defective or there is a restricted air flow.


I have a ball valve installed on mine. Most water valves have a small hole in them to allow some coolant to flow to prevent rust and bleed air.

chuckster
Posts: 109
Joined: Thu Aug 27, 2020 4:53 pm
Location: Meridian, ID

Re: Warm dash A/C

Post by chuckster »

After talking to a service advisor at my local Caterpillar truck dealer I ended up taking the coach in to have the A/C looked at. They are saying that HVAC control head is not allowing heater control valve to open or close. Voltage is present at control head and heater valve, resistance will not change on control head for heat control. They are waiting to hear back from their vendor on price and availability for the HVAC control head so I am bracing myself.

Anyone know where these can be obtained and approximate price for my 2001 Zanzibar 3646 on the Magnum Blue Max chassis?? Part number perhaps?

Thanks!
Chuck in Meridian, ID
'01 Safari Zanzibar 3646 (side entry)
Cat 3126B / Allison MD3060
Magnum M-Series "Blue Max" chassis
Owner since 8/2020

wolfe10
Posts: 93
Joined: Sun Oct 27, 2019 4:12 pm

Re: Warm dash A/C

Post by wolfe10 »

An option if you want the dash A/C to work is to install a ball valve up front on the inlet to the heater core. Close is cool.
Brett and Dianne Wolfe
Ex: 2003 Alpine 38'. Ex 1997 Safari Sahara. Ex 1993 Foretravel U240
Moderator, FMCA Forums 2009-2020
Chairman, FMCA Technical Advisory Committee 2011- 2020
Moderator, http://www.dieselrvclub.org/ (FMCA chapter) 2002-

Ozium
Posts: 3
Joined: Tue Nov 17, 2020 12:45 am

Re: Warm dash A/C

Post by Ozium »

On my 96 the HVAC control head is the same part number as a Chevy Cavalier. If you can get the part number from yours that would be a great start.

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