No Heat

[Speedy2222]

Last fall before i burned up the turbo i noticed that i was starting to have semi-par heat, it would then start to come and go. It eventually got to the point that i just didn't have anymore. My blower motor works, and it will switch positions on the door, but no matter what the temp range i get no heat. I replaced the t-stat last weekend but still nothing. what do i check next?

[Crazy larry]

myte need to pull the dash and inspect the valve for the heater core... I've had them fail and blocked with debris. Good time to replace the neglected heater hose under the dash... Take a couple days and syke yourself up to do it... It's not as hard a job as it sounds..

[Speedy2222]

i'm going to flush it first.. it's almost summer and could just get put off until next year if the flush doesn't fix it.. i did however, just drive it to the gas station and came out to a puddle under the car. one of the hoses on the heater core had come loose.. it was the left one( when looking at the engine from the front), is that supply or return side? 99% sure i have the hoses hooked up right, but i always thought the bypass from the water pump was the feed.

[Shelby]

the water pump is a suction source , so that means any hose connected to it is on the return side.

 

but when flushing you want to feed the pressure and water in the return port ,,this will back flush any trash and not force it further into the heater core

the water valve is normaly used for max a/c and only closes when max a/c is called for , that means the default position is open , but it is possible for it to stick closed just not likely the problem

 

also if you use air pressure to flush the water thru the core do not use excessive pressure .most of the time the water pressure is more then enough to flush out any trash

 

one more thing no heavy power is running thru the control head ,, all it does is control ground signals for relays , the power to run the fan motor comes from the fan control assy

[Speedy2222]

Havn't had the chance to flush anything due not having a hose to flush with, but had full heat this morning. Hoping to do a full flush in a few weeks or so, but for now it's working!

[Shelby]

a common problem is the vac hose comeing off the intake,, it's the one faceing the fender below the inj housing base

[Speedy2222]

hhmm, i know i havn't had to put any back on in the last few weeks, my pcv blew off when the knock box kicked in but i'd think if it knocked anything else off it wouldn't work instead of working like it is

[Shelby]

only takes a moment to look

[ucw458]

The vac hoses have nothing to do with heat. They only direct the air flow. The heater valve and the heat/AC blend damper are controlled by a stepper motor located on the drivers side of the heater box.

 

 

http://i463.photobucket.com/albums/qq352/ucw458/clutch/PIC_0997-1.jpg

[Shelby]

UCW not to disagree but the car has a full time full flowing heater core ,, that means it has heat all the time the coolant is up to temp , you have heat because the air director door causes air to flow thru or around the heater core ,,and that door ( blend air door ) is control's by a vacuum actuator

 

that is the way all auto a/c systems i'm used to working on works,, there is not reason to close off the coolant flow thru the heater core except during times of max a/c useage and during that time the coolant flow from the engine is flowing back to the water pump by way of the bypass hose connected to the metal water pipe at the rear of the engine

[ucw458]

and that door ( blend air door ) is control's by a vacuum actuator

 

no it's not. the stepper motor controls the blend damper and the heater valve.

 

 

 

 

And yes the heater valve doesn't close completely until you select max AC.

[Shelby]

before I fineshed my last post I went completely thru the a/c chaptor quickly to be sure but I found very little actualy talking about the water valve,, guess i'l have to make a more detailed read

i'm not totally saying your wrong , but making it an adjustable step valve would be of little use

but mits may have done so

I beleave I have a complete heater a/c unit out of a car , guess I can take a quick look at the controls tomarrow

[ucw458]

It's not mentioned much in the FSM but it's there. Here's some page references that link them all together.

 

 

Page 24-13 at the bottom of the page

 

 

 

Page 24-23

 

Page 24-90 through 24-92

 

 

 

 

If you think about it, it makes sense to use a stepper (servo) instead of a vac motor. The vac controls are either on or off. So if the blend damper and heater valve were vac controlled then you would only have 2 settings, max heat and max cool.

[Shelby]

max heater flow and no heater flow are all you need,, the temp control comes by controlling how much air is deverted around the heater core

 

you mentioned that the heater temp sensor was not on the 88 you were working on,,

the only system I have ever seen that sensor on was 1 86 flatty and 1 83 starion

none of the 87's 88 or 89s have had it

[ucw458]

If you slow down the flow of hot coolant to the heater core as you approach max AC the heater core wont get as hot and the system becomes more efficient. The heater valve in a SQ varies with the blend damper.

 

 

The sensor described in the pic was there on all the digital AC cars through 87. The 88-89 cars had that switch incorporated into the temp gauge sender. that's why 83-87 cars have a 1 prong gauge sender and the 88-89 cars have a 2 prong sender. That switch allows the AC controller to delay turning on the blower until the coolant warms up when you are calling for max heat.