Rear Heater not functioning

zelseman · 12-11-2016, 09:05 PM

The rear under-seat hurri-hot heater in my 2000 Chevy short bus will not push out hot air. The fan comes on with both speeds, but only pushes cold air after over an hour of driving. The coolant hoses under the bus do not get warm even after an extended drive. There is however, a small drip of coolant at the connection with the heater, so I assume coolant is getting to the heater.

I have opened 3 valves under the hood. One is a main valve that looks to split to the dash heater and one to the rear heater. The other two valves are on the passenger side of the engine bay and are open. There is no valve under the dash or in the cab that I have been able to find. The hoses run down the passenger side underneath the frame and cross over near the rear axle.

Any ideas why I am not getting heat? The dash heater puts out heat just fine I am at a loss.

superdave · 12-12-2016, 06:46 AM

the fins on mine were packed full of dirt, does the heater core itself feel hot? if not take it out and check to see if its pluged up. run water backwards thru it.

zelseman · 12-12-2016, 08:10 AM

It feels warm after an hour of driving, but definitely not hot. Not nearly as hot as I remember those things getting as a kid. I'll take it out tonight and run water through it. Thanks!

Tango · 12-12-2016, 09:27 AM

When I pulled the non-heating rear heater from my old bus, there was easily 30 pounds of dust, hair and assorted grahdoo packed into the fins. I gave it to a friend who cleaned it and installed it in a stix & staples he was rebuilding, Worked like a champ.

leadsled01 · 12-12-2016, 09:45 AM

My short bus has a valve along the frame rail for the rear heat. Roasted my azz off for the entire first summer before I found it..

DoubleO7 · 12-12-2016, 10:05 AM

if coolant is flowing through the heater, both the in and out hoses will be warm enough that you do not want to hold onto them but for a few seconds.
If they are stone cold, you have no flow due to another valve still closed or obstruction of some sort.

zelseman · 12-12-2016, 04:17 PM

I took the heater core out this afternoon and found it caked with dirt dobber nests and all kinds of fun junk!

I am waiting on the core to dry up from the hose and I will update on the status.

Tango · 12-12-2016, 05:37 PM

That looks positively clean compared to what came out of my old Blue Bird. You couldn't even see the fins for all the fuzz and debris.

The melted bubble gum was the worst part.

zelseman · 12-12-2016, 08:53 PM

So i hooked it all back up and still no dice after a 40 minute drive with the fan on and the dash on high heat. I am at a loss. I guess there is a blockage somewhere in the line and I don't think I want a rear heater bad enough to replace 40 ft of coolant hose under the bus. Thanks all for the help!

Tango · 12-12-2016, 10:57 PM

Ya...if the hose isn't hot by the time the engine is up to temp...then the heater unit is not the problem.

AlleyCat67 · 12-12-2016, 10:59 PM

You sure there's not a valve hidden somewhere that needs to be opened? I mean I don't think they would hide them but it could be in an out of the way place..... I know you mentioned three under the hood but there could be another one somewhere.

superdave · 12-13-2016, 06:26 AM

or a bad gate valve, there the worst. do you have a circulation pump? any switches say pump?

DoubleO7 · 12-13-2016, 08:04 AM

if it is blocked with crud versus a valve, I would be worried about the rad being about blocked also.

Maybe a hose is kinked or pinched shut somewhere?

Make sure the in and out hoses from the heater are actually connected to return fluid to the rad. If the return to rad hose is blocked off somewhere other than a valve, it will not work either.

2kool4skool · 12-13-2016, 09:48 AM

Quote:

Originally Posted by superdave

or a bad gate valve, there the worst. do you have a circulation pump? any switches say pump?

If you gate valves they are known for failure. Our BB, for example, has ball valve.

2x on the circ. pump.

cadillackid · 12-13-2016, 10:32 AM

most cutaways dont have circulation pumps, however there is often a second heater valve installed near the dash-heater vslve under the hood.. sometimes its a vacuum operated valve tied to the dash heater.. of course im sure you are running your dash heat so we know that valve is open.. its normaly near the passenger side firewall on a cutaway bus.. you'll see the silver A/C lines if your bus has A/C, but that valve is normally in one of the black heater hoses up near the firewall.. if its an automaticone and has a little vacuum line connected to it.. tap on it with the Handle of a hammer (not the head..) they do stick..if its a manual, you can open it.
-Christopher

zelseman · 12-13-2016, 10:09 PM

These are the valves that I have found under the hood. Maybe this will answer some questions about what setup I have. I do have working dash heat and it warms up well and fairly fast.

cowlitzcoach · 12-14-2016, 02:12 AM

I assume since you have had the heater core out that you have since bled the air out of it. It is fairly easy to get a vapor lock in the loop and no amount of driving will move the vapor lock out.

In a bus without a heater booster/circulation pump the only way in which hot water moves is by way of the engine's water pump. If there is an easy way for the fluid to flow it won't take the difficult way. It doesn't take much air in the system to completely stop it up.

Somewhere on the heater core there has to be a bleeder screw. If there isn't then you will need to crack a hose to make sure you are getting flow out of the hose and into the heater core.

If you don't get anything out of the bleeder screw or from cracking the hose you have some sort of obstruction in the circuit between the engine and the rear heater. You will need to follow the full length of the hose circuit. At every joint you will need to crack it open to find out where the blockage is occurring.

Good luck and keep us posted at to your progress.

zelseman · 12-15-2016, 07:59 PM

Quote:

Originally Posted by cowlitzcoach

I assume since you have had the heater core out that you have since bled the air out of it. It is fairly easy to get a vapor lock in the loop and no amount of driving will move the vapor lock out.

In a bus without a heater booster/circulation pump the only way in which hot water moves is by way of the engine's water pump. If there is an easy way for the fluid to flow it won't take the difficult way. It doesn't take much air in the system to completely stop it up.

Somewhere on the heater core there has to be a bleeder screw. If there isn't then you will need to crack a hose to make sure you are getting flow out of the hose and into the heater core.

If you don't get anything out of the bleeder screw or from cracking the hose you have some sort of obstruction in the circuit between the engine and the rear heater. You will need to follow the full length of the hose circuit. At every joint you will need to crack it open to find out where the blockage is occurring.

Good luck and keep us posted at to your progress.

I actually haven't bled it since I had the heater off to clean it. I have a bleed screw on top of the motor, I will bleed it and see if that helps.

superdave · 12-16-2016, 06:49 AM

take the return line from the heater core off and start the engine cold. the thermostat will be closed and the pump should be pumping the antifreeze thru the heater cores. leave it off for 30 seconds to get the air out.

zelseman · 12-24-2016, 06:20 PM

I figured out my problem. Despite my understanding of valves, the yellow valve in the 2nd picture is actually closed in that picture. I turned it and shortly there after I got heat.

Thanks for all of the help!

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