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Don,

Go to the engine bay and watch the dash A/C compressor. If it kicks in and holds then the compressor is most likely not the problem. If on the other hand, the compressor clutch cycles in and out every 30 seconds or so, you likely have a freon related problem. I don’t think this problem is one to be solved under the old shade tree.

Of course there is always the old thrown/loose belt, but being like me who works best under the shade of an old tree, I’ve got to believe you have already made this check. If not, STOP the engine and check the belt tension. It may be the belt is loose and not providing the proper compressor operation.

Your evaporators likely have filters for recirculation of ambient air inside the coach. Find them and clean or replace them so the ambient air actually gets to the evaporators.

That is about the limit of my information for the simple things to check before laying out the $$$ for an expert analysis.

[Archived]

Don,

The Prevost OTR system has a loop dedicated to the dash air. The short version is the loop is controlled via a solenoid valve which in turn is controlled by the temperature knob.

I would see if the solenoid (I think it is in the condenser bay, but check with the service manual available here: http://prevostparts.volvo.com/technicalpublications/en/wiring.asp

I would start by checking to see if the solenoid is getting power to the coil when the system is on and calling for AC. If there is power to the coil suspect the coil. They are replaceable. If there is no power suspect the control.

There is an OTR system webinar on the Prevost site, accessible through the commercial side. That will be a big help to you.

[Archived]

Most liberty’s have otr air, if it does it has only one large compressor for the whole coach, if so it may have a orfice in the front evaporator stopped up

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Will,

He has OTR, no seperate dash air compressor.

[Archived]

I opened up my paper Prevost mx manual and it directed me to the frt compartment behind the reclining front bumper to a liquid refrigerant solenoid valve just above the pass side basement air. This valve controls the flow of refrigerant to the driver area evaporator. It is controlled electricly with the rheostat on the dash. The mx manual said it can be manually bypassed by removing the bonnet(cap) and turning the 3/16″ manual operating stem ccw a half turn. When I removed the cap, I found the manual operating stem turned open all the way. When I moved it to where the mx manual said to it started spaying freon out so I put the cap back on quickly before I lost much freon an. I did not disconnect the elec power to this solenoid valve. I started the coach and checked to see if the dash part of the system was getting cool. It was NOT. The main passenger compartment was cooling good still. I ran out of time. Tomorrow I’ll disconnect the elec power to the coil on the refig solenoid valve and see if the dash air gets cool. I know the solenoid valve is getting power because the coil on it is getting warm. I;ll put a multimeter on it tomorrow too. I’ll also tap on it a time or two in hopes of freeing it up.

I may have to open the system to repair or replace this refrigerant solenoid valve.

Maybe the dash system is blocked down stream, before the dash evaporator somewhere?

Your thoughts?

[Jerry]

If the solenoid coil has power (because the coil is warm) it suggests to me the dash temperature control is working. Because it is getting power (and has not failed something I am guessing because it is warm) the problem is likely elsewhere. Does that loop have an expansion valve that could have failed?

[Archived]

Don,

Forget what I said yesterday. I skimmed through the words and was mislead by you signature. I know nothing about Prevost OTR aside from what Jon and Tom say about it.

[Dale]

I had the front panel off under the dash yesterday looking at my electric wiper system. I noticed the air door for the driver that is controlled by the knob on the dash was filthy. So was the filter under it. So dirty that even the evaporator or whatever that is beneath the filter was also filthy. Not sure if this has anything to do with your issue, but it seems like it could sure keep cool air from coming through.

Of course, my bus air don’t work anyway. Freon tank is bone dry. My system has been converted to R134. Someone told me that you have to put all new hoses on or the 134 will leak out. Not sure if this is correct. The conversion was done at Prevost Nashville. But anyway, all the freon is gone. Gonna get a buddy of mine to leak test it next week. I heard you could get a deal on 30 lbs of 134 at Costco. Hopefully, freon will get it working. Oddly enough, even the fans don’t blow. Wondering if there is some sort of lockout that stops the whole system if it gets low on freon.

[Archived]

The dash evaporator is not getting cold. I manually opened the refrigerant solenoid valve and disconnected its electric coil. The expansion valve is getting cold, 45 degrees. The lines coming and going to it are getting cold, but I quess there isn’t enough flow to get the evaporator cold soaked. The capulary tube coming out of the top is mighty short and goes nowhere? That doesn’t seem right. I may order a new expansion valve, Prevost pt# 95-0221 made by Parker Hannafin, and replace it which requires evacuating the system. I do all my own ac work and have my own ac equipment, but I don’t have a way to recover 25 Lbs of freon. My friends that are automotive shop owners can only recover a max of 15Lbs.

Where’s the least expensive place to buy parts for our Prevosts? I’ve owned 4 tags axle Monacos. The last place I would order parts was from Monaco.

Refrigerant Solenoid valve location

Refrigerant Solenoid valve

Expansion valve location

[Archived]

Don,

On later models (I am not sure about older models) you can pump down the system and should be able to capture the freon in the system. I may be thinking about pumping it into the big receiver so your can work on the compressor. If you can shut off the driver’s air loop from the rest of the system you only have to recover the refrigerant in that loop.

[mike]

A friend(retired bus mechanic) helped me get the OTR air dash curcuit air blowing 50 degree air, which is 25-30 colder than ambient, on a 90+ degree humid TX day. We installed a new dash curcuit expansion valve, Prevost #950221=$71+ shippping. I purchased a liquid refigeratant solenoid valve repair kit too just in case, but we didn’t need it.

When we started the work, the OTR air system was properly serviced w/R134. We shut the lower valve on the receiver, started the engine and pumped most of the liquid R134 into the receiver, stopped the engine when the low pressure switch disengaged the compressor clutch at about 15 psi. Quickly changed the dash expansion valve w/new (don’t forget 4 new o-rings). We opened the lower receiver valve as we were tightening the last expansion valve fitting(upper right comes from receiver) to purge any air out out of the line. It wasn’t necessary to add any freon afterwards. Yeah!!!

How bout them SPURS

[Archived]

Spurs awesome ! Cold AC even better !!

[Dick]

Yep… what George & Becky said !!!