Dash AC problem

[Alek&Lucia]

Hello everybody,

Question:
My dash air is not cooling latelly,( fan working good ) but my OTR AC is working fine. Where would you start looking for the problem ?

Alek

[Petervs]

Go look at the engine while idling, have someone turn the dash air on, and see if the compressor clutch engages when the switch is turned on. If the magnetic clutch makes the compressor run, and there is no cold air after a few minutes, then you might have low freon caused by a leak.

That is what I would do first. The dash air has its own separate compressor, much like on a car.

[merle&louise]

Alex,

I watched an AC tech charging my dash AC system with freon. It was a very simple process: he watched the sight glass while the engine was running with the dash AC running on high. When he would see bubbles in the sight glass he would tell his helper to add a little freon. They did this for about 20 minutes until there were no more bubbles in the sight glass. We went inside the coach and the dash AC was blowing ice cold air. It really is a simple procedure; the key is to add just a little bit freon a time and wait to see if the bubbles disappear.

[dale farley]

Alek,

Hopefully, the advice given above will solve your problem. If it does, you may have a small leak that will periodically require a small charge.

If that doesn't solve the problem, you will need to look at your compressor pressures to see if there is a problem there. If the compressor is working correctly, and you still have no cooling after trying to charge the system, you may have to check the expansion valve to make sure it is not clogged up. It is located where the freon line attaches to the evaporater under your dash.

[Jon Wehrenberg]

Dash air on an OTR equipped coach does not have its own compressor. It has a solenoid valve which opens the circuit to the evaporator for the dash air.

Another problem is the mixing valve which admits heated coolant to temper the air my be defective, but if that was the case instead of just air blowing, it would be heated air.

I do not know how the H3 is set up or how to access the solenoid valve.

[Jerry Winchester]

I had a similar problem (dash AC wasn't as cold as the coach) and they discovered the dash AC expansion valve was allowing too much flow thru it (not enough expansion I guess).

It was swapped out and the discharge temp went from 63 to 47. Much better for sure.

[Alek&Lucia]

Thank You everybody,
Like Jon said when you have OTR you have only one compressor,that is why I posted in my original post that the coach side is working good but not the driver dash.
Do I have to go to Prevost service or good Truck Shop like Kenworth will be OK ?

Alek

[Jon Wehrenberg]

Alec,

If it is a bad solenoid valve for example the system has to be opened and someone familiar with it needs to vacuum the system and recharge it after the valve is replaced.

If it is in the thermostat (the temperature knob that controls) the solenoid it is an easy fix but to diagnose it requires that you get at the valve to rule out whether that is the problem or not. I do not have H3 manuals so I have no clue where the stuff for the driver's air is located or how it is wired.

My guess is to see if the Prevost folks can talk you through some basic diagnosis. I would not want to pay a truck place to do on the job training.

[Steve Bennett]

I would also say the likely culprit is the dash evaporator expansion valve. We have replaced 2 on OTR equipped coaches.

[Jerry Winchester]

You can access the valve by lowering the front bumper and looking straight up into the area above. You could tell by feeling the valve it was not working well since the unit was full of Freon and the compressor was functioning properly.

I would want someone who knows what they are doing to look at it. If they can't find the valve, then I would punt. And you have to remove all the Freon from the system, change the valve out then vac it all down and refill. Not a lot of work, but you have to have one of those snappy reclaimation units. Prevost fixed ours.