original bus heat

[oldallegro]

Top of the evening all,

My 1990 MCI is giving me heat trouble these days.  We are in CT and the temp is dropping steadily.  I have radiant heat in the floor and below the bays, but we left the original bus heat in as well for when we are driving and heat is being taken away from all the surface area of the bus.  Anyway, when I am driving, the blowers put out warm air for about 3 to 5 minutes.  Then it is very cold.  If I wait an hour, sometimes I get more warm air.  I think the warm air is from the radiant heat lines warming the air in the heat ducts.  I have checked all the valves for the original heat and am still not sure what might be causing the problem.  The defrost system for the driver is always hot. 

Kurt

[captain ron]

You might want to check your radiator that is in front of your front bay and make sure it is not clogged or a valve there shutting it off. Check coolant level,

[captain ron]

There are 2 valves in the engine compartment one above tranny and one on curb side by frame rail. you may have valves by the front radiator.

[oldallegro]

I checked the two rear valves, but did not know there might be one up front.  I will check that.  I am curious how the defrost for the driver works when the normal bus heat does not.  Aren't they tied together?

[NJT5047]

Not sure what MCI you have, but most of that vintage have a large heater control valve in the upper RH front bay.  Get the bus warmed up and feel the hoses for heat on both sides. 
Your temp guage is indicating that the engine is at 180 or so?  If so, the heater hoses on both sides of the valve should be hot.  If not, the heater control valve may be at fault, or the control may not be calling for heat?
It sounds like a small amount of heated water is getting thru the lines.
Have you drained the chassis coolant for any reason?  Not sure if this woud cause a "no heat" condition, but the heater cores generally have to be bled by opening vents on top of the cores. 
JR

[Tony LEE]

There are two valves in the engine compartment and one next to the driver. Since the defrost is working then all three are ON.

The electric valve in the front right luggage bay is normally on - ie on when no power is applied -- so first thing to check is whether there is power supplied to the valve or not. No power means the temperature controller is calling for heat, so if there is no heat then valve may be jammed shut.

Power on the valve all the time  means the temperature control system may be faulty.

Note that feeling the pipe either side of the valve close to the valve may not help much because it is all copper and brass and normal conduction will transfer heat for several inches past the valve.

_____________________________

As an afterthought.
I still have the original bus air on and when I first switch the cooling on, the bus actually heats up for a couple of minutes because the heating coil is full of hot water because the valve had been depowered as the heating/cooling system was off. As soon as the cooling switch was closed the valve shut and stayed shut until the bus cooled down to the set temperature at which time the hot water valve is controlled on and off to maintain the set temperature.

Perhaps while you were pulling the cooling system out, you have mixed up the cooling and heating functions and the system is actually in the cooling mode instead of heating. This would explain the initial 2-minute heat surge and the heat surge at long intervals afterwards.

[lyndon]

I think you should determine whether the radiant heat is giving a bad message to the control valve. A quick check would be to disable the radiant heat, if you can, and go for a ride. If the bus heat works normally, you'll know which problem you have to solve.

Don

[Jerry32]

You didn't say what the thermostat control was indicating. the led temp shows what temp it is seeing . mine heats fine as long as the indicated temp is lower than the set temp. Jerry

[Sammy]

Kurt, just unplug the electrical connector at the main hot water valve and you will have "full" heat from the stock system.This will give you a temporary fix - heat only with no control of it. What model MCI do you have?
In the first cargo bay on the curbside,look at the top right corner, you will see a plastic cover.
Remove screws and there's the valve.Some valves are air actuated, have a small solenoid mounted on it  with an air line too.
I have seen and replaced only the solenoid, coil was "open".
Good luck.