Heater blowing cold air

[bigbob70]

I have a 28 ft 1988 Itasca, class A, Chevy 454, P30 frame...

When I turn on the heat cold air blows out the floor and dash vents and when I switch to defrost, same thing...Cold air...

Where do I begin??

 

[Rene T]

Deleted

 

[Papachazz]

The first thing I would check is the connections going in through the firewall into the heater core. If they don't get hot when the engine is hot then they may be clogged at the radiator or somewhere in between. You might try flushing the radiator a couple of times and see if that gets the hot water flowing. If not then the next step would be to check the heater core itself. Replacing those can sometimes be a chore but the cost of a new core is really not that expensive.

 

[HappyWanderer]

Check the coolant level first. If it's low, there won't be any at the heater core and you'll get no heat.

 

[bigbob70]

Coolant level is full..I know this because when I went to take the radiator cap off fluid came out...

As suggested, I'm going to try flushing the radiator a couple of times and back flushing the heater core and see what happens...

I'll report the results

 

[kdbgoat]

It could also be a problem with the blend door operation or someone put a bypass setup on the lines that run to the heater core. Or even a valve on the lines. Is this coach new to you?

 

[Gary RV_Wizard]

Two things need to happen to get heat up front:
(1) the engine coolant needs to be hot and circulate through the heater core. Sometimes there is a manual valve in the hot water line to the heater, installed when usual dash-controlled valve fails (this was a common problem on the Evan Tempcon dash HVAC system), so if this coach is new-to-you, check for that. The valve has to be manually turned off in the summer for a/c and on when you need heat. If it doesn't have the manual valve "fix", it may be that the regular valve controlled from the dash isn't working either. Usually that results in heat all the time, but the opposite failure mode is possible too.


(2) there is an air blending door that mixes heated and unheated air - that is how the temperature control adjusts the air you feel. If that is stuck, you may not be getting any of the heated air into the cabin.

 

[John Canfield]

Has it ever worked?  Some will bypass a leaky heater core instead of replacing it which can be expensive if you have it done or time consuming if a DIY project.

 

[bigbob70]

Has it ever worked?  Some will bypass a leaky heater core instead of replacing it which can be expensive if you have it done or time consuming if a DIY project.

No, it has never worked...I'll dig into it tomorrow and report back.

I'll check that first thing to see if the heater core hoses are hooked up...

 

[John Canfield]

Even if the hoses are hooked up, make certain there isn't a valve inserted which is in the closed position.

 

[Gary RV_Wizard]

If it has never worked, chances are good that somebody installed a manual shut-off valve in the heater hose. Failures of the Evan Tempcon control valve were common back then, and a replacement was relatively expensive, so many owners and even a/c shops installed inexpensive manual water shut-offs in the hose near the heater. Made sense for those who only traveled in summer weather and used a/c a lot more than heat.

 

[bigbob70]

This morning I got started on fixing my heater...I removed the "doghouse" and staring me in the face were the two heater hoses that go to the heater core..I thought to myself that it can't be that simple..

I disconnected the heater hoses at the "T"..Two hoses ran foward and two ran aft..I disconnected the two running forward and used my brass tapered hose end w/shutoff between the hose end and brass nozzle..

I few shots of water and out came the rusty junk that had collected in the heater core..To be honest I was expecting a lot worse.. I flushed the front and rear heater cores then buttoned everything up..I then pulled the lower radiator hose and let it drain, then reconnected the hose...I refilled with water then added some radiator flush and let the engine run for about 20 mins...

I checked the heater and VIOLA, hot air...I drained the radiator flush and even left the bottom hose off the radiator while letting the engine idle to pump more old stuff out...Yea, I kept my eye on the temp gauge..

After refilling with about 4 gals of anti-freeze I cranked it up again just to reassure myself that I still had hot air...Yep, working good..I can't beleive it was that simple..I was expecting a lot worse

Thanks everyone for your input which as usual was right on...

 

[Gary RV_Wizard]

Once in a while you catch a break! Maybe you should buy a Lotto ticket while your luck is running strong!

 

[Papachazz]

Great Bob! It sure is nice when you catch a break with those simple fixes. Glad it worked out for you. 

 

[John Canfield]

Ah-ha - we called that one correctly!    Glad you got it squared away.