How strongly does OTR air blow?

Midwilshire · May 28, 2012, 05:57:37 AM

I tested the OTR air on my 78 MC5 during a 1 hour trip yesterday, and neither the drivers nor the passengers cooled much. The drivers blew hot air, and the passengers let's out a little cool air, but one would be hard pressed to say it was "blowing.". I plan to keep the drivers air and fix it up, but still trying to decide about the passengers OTR system.

So, my question is, how hard should it be blowing at the passenger windows? I can barely tell that a blower is on at all. I checked the squirrel cage blowers in the AC bay, and they're running fast, but I can't figure out where the air is going.

Thanks,

Mike

lostagain · May 28, 2012, 07:00:58 AM

Sounds like the whole system is low on freon. The coach should be cooled down in 10 mn on a hot day.

The cold air comes out along the bottom of the windows. Not really strong at any one spot, but a lot of volume throughout the whole bus.

At the driver's, you should feel a stronger flow.

And make sure the heater hoses valves are closed in the engine compartment, and the one to the left and below the driver. See the operator's manual.

JC

muldoonman · May 28, 2012, 09:19:24 AM

Mine blows like a whirlwind in front on high and more so in the back of coach. There is no adjustment for airflow in middle of bus just temp setting at front control. This is on a prevost. Front and back air. The blower setting wasn't affected when there was no freon.

bevans6 · May 28, 2012, 10:21:04 AM

The drivers A/C and the OTR A/C use the same compressor and condenser, but there is a separate drivers evaporator. So keeping the driver's air and ditching the OTR air is not really an option without a lot of rework. Mine blows air out at the base of the windows.

Brian

Van · May 28, 2012, 10:33:46 AM

Are there filter packs on your system? if so... might need cleaning. JMTC

RJ · May 28, 2012, 12:22:51 PM

Quote from: van on May 28, 2012, 10:33:46 AM
Are there filter packs on your system? if so... might need cleaning. JMTC

Good point, Van!

IIRC, on the MCIs of this vintage, the HVAC filters are accessed on the curb side in the coach battery bay. But double-check their location and access in the shop manual, since I'm far more familiar with GMCs.

They're usually disgustingly dirty, but a thorough cleaning should improve the airflow tremendously. Don't operate the system without the filters, either!

And if all you're getting is hot air out of the system, it may, in fact, be low on "freon" and needs to be recharged - AFTER a leak test.

I believe MCIs of this vintage also had their HVAC system operate very similar to GMC's. GM used heat to regulate the temperature of the A/C output. They run the compressor full-time, and cycle the heat on/off to maintain temp control in the main cabin unit. This does not affect the driver's A/C evaporator - he controls that with the lever to the left of the driver's seat. So shutting off the heater valves in the engine compartment may affect the overall output.

Read your shop manual for a complete explanation.

FWIW & HTH. . .

bevans6 · May 28, 2012, 12:49:53 PM

RJ is correct in how the MCI temp control works. The A/C is full on all the time, and the temperature is controlled by the heater valve in the passenger side engine compartment. The flow of heat counters the cold air produced by the A/C. The heater valve is an electric on/off valve controlled by an electrical circuit that I have never been able to figure out, but is basically a variable resistor on the panel beside the driver's left knee, and a temp sensor in the cold air return duct in the middle of the floor (under a seat if the bus still had seats). If you cover up those ducts or take out that temp sensor, you are out of luck as far as OTR A/C is concerned, and OTR heat will simply run on full heat all the time. The driver's heat valve just controls the amount of hot water flowing in the driver's heater core, which in turn balances the cold air created by the driver's A/C evaporator in the dash.

Brian

lostagain · May 28, 2012, 05:14:05 PM

RJ and Brian are correct about the hot water valves counteracting the A/C. However I remember that often they don't work, and to get cooling in hot weather, you have to turn off the valves by hand.

JC

Hi yo silver · May 28, 2012, 06:47:49 PM

As mentioned above, the air blowing below the windows isn't very forceful, but there's a lot of volume. When I got my bus, I cleaned all the filters and condensers, which were really dirty, found the freon was low, and after pulling out the little remaining freon, refilled with Freeze 12. That was two and a half years ago and it will still freeze the unowhat off a brass monkey. Just my experience.
Dennis

RJ · May 28, 2012, 09:34:36 PM

Forgot to mention that one of the other reasons GM/MCI designed the system this way is that the heat acts as a dryer to help evaporate moisture and condensation w/in the system.

FWIW & HTH. . .

Midwilshire · May 28, 2012, 09:38:57 PM

Thanks for the informative replies!

In the end, I decided to pull the OTR and drivers heat. Will get an aftermarket condenser for the drivers AC.