[Mike & Brigitte]

Here is what my Prevost Owner Manual says:

“A/C” warning light

This light is designed to light up when the “A/C” system is not working properly. If this happens, first stop “A/C” system, then perform the following checks:

Check the condenser for obstruction. Clean if necessary. (Refer to “Maintenance Manual”).

Check that the evaporator and condenser motors are operating.

Check evaporator filter for cleanliness.

Clean or replace as required. (Refer to “Care and Maintenance” section, page 6-9).

Check the air return duct(s) for obstruction. Ducts are located on the left side or on both sides of the vehicle floor, approximately in the center. Clean if necessary.

After these checks, test the system. If the “A/C” warning light does not turn off, set the “A/C – heat” switch to “OFF” position, and seek qualified service assistance.

So, it’s an “AC Warning” light. Maybe for high pressure or maybe for low pressure. In your case it sounds like its for low pressure because the system isn’t blowing cold air. The low pressure safety switch will cycle the AC system on and off.

On our bus, the evaporator and condenser fan relays, R38 & R39, in a box in the condenser bay(see pic), have a high failure rate. I change them every few years before they fail.

[DON]

Don thanks for the recap as will proceed and see what the issues are.

Thanks,

[Jeff]

If all is well with the items mentioned previously,

IMO, the most likely cause of your problem is:

low on freon. Connect AC gauges and see what is what. Find the leak and fix it(easier said than done). Compressor clutch shaft seal may be the problem. Look for oily residue.

Other causes could be:

Evap or Cond relay is bad causing associated fans not to come on so resulting in a hi or low pressure safety switch activation(this has happen twice to our bus)

or

Dryer filter is clogged causing safety pressure switch activation(this happened to our bus a couple of yrs ago),

or

Bad safety switch,

or

unloader valve(s) not operating properly.

[Jon]

Turned out to be a defective condenser fan motor…. bearing failure on front fan motor caused intermittent outage, shutting down OTR. Thought it maybe brushes in motor but turned it to be bad bearings. bus air won’t work on one fan operating….

[Art]

Glad you found the issue, Brady. I can only assume Tommy Duhon found it. Is he going to replace it for you also? 😉

Seriously, how did you find it?

[Richard]

Not likely, been on the road 3 weeks so will see Tommy when home tomorrow!!! I will tell him you suggested he check it…..

tks

[AL]

I have working on my dash air, Looking at electrical schematics for both standard ac and OTR ac I cleaned the 3 sensors 1st Hi limit is 245psi to 320psi -2nd is Low pressure 5psi to 30psi – 3rd radiator fan sensor 130psi to 170psi, Looking at the way they are plumbed in and wired in to low psi compressor clutch won’t come (no cool)- Hi psi compressor clutch won’t come on(no cool) and you get a light on dash. All the sensors protects the cooling system.

[Paul]

Art when I did mine there was a minute plus time delay in the circuit. I do remember it was in rear box.

[Paul]

Yes in rear box there is a time delay relay in rear from AC clutch switch on dash that’s what start’s the whole thing, you can see it on schematics below HI & Low sensors.