Excess heat inside the car GT500KR

[GT350AUS]

Does anyone else have excessive heat inside the car?


Went for a drive today and found there is a  lot of Heat coming into the car,  like the heater is blowing hot air into the cabin area.

The hood seal is fine so nothing getting into the cowl area.

I'm tempted to bypass the heater core to rule out a problem in the heater box or cables shutting down the heat flap from the box.

It is an a/c car.

Anyone have any ideas as to what could be causing it?

[Rickmustang]

Big blocks are hot, but did you bypass the heater core? If not the water valve in engine compartment may have failed. This assumes the vacuum controls are hooked up correctly under the dash. My 68 had AC, and my 70 big block car does too. I hate under dash projects due to all the AC stuff.

[GT350AUS]

Haven't bypassed the heater core yet but that's the first thing I will do to rule out a heater box or as you suggest the water valve in the engine bay.

[Bob Gaines]

Big blocks are hot, but did you bypass the heater core? If not the water valve in engine compartment may have failed. This assumes the vacuum controls are hooked up correctly under the dash. My 68 had AC, and my 70 big block car does too. I hate under dash projects due to all the AC stuff.

Probably not the heater hose valve. That valve only closes off the flow of water in the heater hose when the A/C is on. If the A/C is not on the water flows through the valve and through the heater core whether the heater is on or not . I suspect ether faulty vacuum or faulty duct function in the heater box.

[GT350AUS]

Thanks Bob, if it is a faulty vacuum or duct function is there any way to check it without pulling out the heater box?

[Coralsnake]

I once had a KR with similar issues. Make sure all the rubber plugs are intact on the firewall

[427heaven]

Everyone has added something that may contribute to fixing your possible problem. Most of my cars are big block powered and some have the propensity to run angry hot if allowed to do so. Trouble shooting is an analytical process, start off with the heat source. Is the heat coming from the cabin or from the engine compartment, run a bypass hose on your engine eliminating any hot water from entering the cabin area. A simple loop to eliminate the heater hoses from going into the car, Drive it around and see if that fixes the problem. Does ANY heat seem to be coming in from the firewall area at least what might seem abnormal to you. Since its winter time it will be easy to feel, plug any firewall or floorboard holes allowing heat into the car. Move on down the line to any inside car items, heater core, valves, hoses, controls etc. you should be able to see or feel if hot air is coming from the plenum or somewhere else. Use all you senses and you will be able to decipher where your trouble is coming from. Good Luck!

[Royce Peterson]

(Edited 2/2/2020 because Bob is right)

Bob the valve that ports vacuum to the hot water valve is closed unless the temp cable is moved to the lower position. So water only flows then. It does not matter if the fan switch is on or off. So the only time heat should come from the system is when the cable is moved down, which also opens the heat door. The hot water valves are spring loaded open. When they fail, they fail open. The heater core does get warm anyway just from the stagnant water eventually getting warm through contact. But it will not be as warm as it could be if the valve were open.

The fan switch controls the air conditioning compressor power, in combination with the icing switch. Turning the fan on will supply 12 volts to the fan clutch unless interrupted by an open icing switch.

If you are getting warm air in the cabin it is most likely the foam rubber in the heater / AC box is rotten and allowing air to get through / around the closed heat door. 

Another possibility would be someone has purposely disconnected or plugged vacuum to the heater valve so it is open. You can check this easily by removing the vacuum hose from the top of it with the heat cable set to full cold. There should only be vacuum when the heat lever is at the top and the engine is running.

Big blocks are hot, but did you bypass the heater core? If not the water valve in engine compartment may have failed. This assumes the vacuum controls are hooked up correctly under the dash. My 68 had AC, and my 70 big block car does too. I hate under dash projects due to all the AC stuff.

Probably not the heater hose valve. That valve only closes off the flow of water in the heater hose when the A/C is on. If the A/C is not on the water flows through the valve and through the heater core whether the heater is on or not . I suspect ether faulty vacuum or faulty duct function in the heater box.

[Bob Gaines]

Bob the valve that ports vacuum to the hot water valve is closed unless the temp cable is moved to the lower position. So water only flows then. It does not matter if the fan switch is on or off. So the only time heat should come from the system is when the cable is moved down, which also opens the heat door. The hot water valves are spring loaded shut. When they fail, they fail shut. The heater core does get warm anyway just from the stagnant water eventually getting warm through contact. But it will not be as warm as it could be if the valve were open.

The fan switch controls the air conditioning compressor power, in combination with the icing switch. Turning the fan on will supply 12 volts to the fan clutch unless interrupted by an open icing switch.

If you are getting warm air in the cabin it is most likely the foam rubber in the heater / AC box is rotten and allowing air to get through / around the closed heat door. 

Another possibility would be someone has purposely routed vacuum to the heater valve so it is open any time the engine is running. You can check this easily by removing the vacuum hose from the top of it. There should only be vacuum when the heat lever is at the bottom and the engine is running.

Big blocks are hot, but did you bypass the heater core? If not the water valve in engine compartment may have failed. This assumes the vacuum controls are hooked up correctly under the dash. My 68 had AC, and my 70 big block car does too. I hate under dash projects due to all the AC stuff.

Probably not the heater hose valve. That valve only closes off the flow of water in the heater hose when the A/C is on. If the A/C is not on the water flows through the valve and through the heater core whether the heater is on or not . I suspect ether faulty vacuum or faulty duct function in the heater box.

Royce,I did not mention anything about a control in my post only the heater hose valve. If you think that the water valve on the heater hose is normally closed then you are misinformed .   The valve closes when vacuum is applied . It snaps back open when that vacuum stops. It is designed so that if the A/C is on the flow of hot water is stopped so that the heater core is not fighting the evaporator core.

[GT350AUS]

Guys, thanks for your suggestions.

As i mentioned in my initial post my first step will be to bypass the heater core to isolate heat in the heater box.

I'm in Australia, being summer and bushfire season here at the moment i've got a hot couple of days with temps expected to be around 110 deg Fahrenheit. Obviously I don't need extra heat in the car.

[GT350AUS]

So I found a link which I included in this post and it gives a great view and description of what is going on with the Selectaire system.

I does mention the operation of the heater control valve

3. Electrical and vacuum functions are illustrated here. When you apply heat, you are moving the Bowden cable, which affects the heat control door and hot water valve function. The hot water valve is either on or off depending upon vacuum application. Each vacuum port at the vacuum regulator directs vacuum to the appropriate servo motor depending upon control position.


http://www.mustangandfords.com/how-to/interior-electrical/1601-troubleshooting-classic-mustang-climate-control

Can't road test today as it is bad and stormy weather in Melbourne so I've done just run it in my garage.

What I found so far is the vacuum is operating fine as it changes direction of air flow from screen to face to floor so the doors are operating.

However I found that in the off position on the 1 lever and with the cool setting on the centre lever of the control which runs the Bowden cable the fan running in all 3 speeds blows air into the floor area  just like when it is in the heat position.

So I'm thinking that either the door doesn't fully close or the foam is deteriorated. The amount of air passing through is the same so I don't think it deteriorated foam with a closed door as the closed door should still reduce the air flow even if it allows some through.

The door actuator is moving all the way in and out when operating the Bowden cable to and from the heat position so its moving the door from open to closed, but is it closing all the way.

So I'm wondering if there is any adjustment that can be made to close the door totally shut without having to pull out the box.

Just another note....the centre lever doesn't sit in the up position (cool) when i let go of it as it springs down a little, but it will sit in the down (heat)

[Royce Peterson]

Deleted

[Bob Gaines]

Disagree. The valve opens when vacuum is applied. Otherwise it is closed.

Bob the valve that ports vacuum to the hot water valve is closed unless the temp cable is moved to the lower position. So water only flows then. It does not matter if the fan switch is on or off. So the only time heat should come from the system is when the cable is moved down, which also opens the heat door. The hot water valves are spring loaded shut. When they fail, they fail shut. The heater core does get warm anyway just from the stagnant water eventually getting warm through contact. But it will not be as warm as it could be if the valve were open.

The fan switch controls the air conditioning compressor power, in combination with the icing switch. Turning the fan on will supply 12 volts to the fan clutch unless interrupted by an open icing switch.

If you are getting warm air in the cabin it is most likely the foam rubber in the heater / AC box is rotten and allowing air to get through / around the closed heat door. 

Another possibility would be someone has purposely routed vacuum to the heater valve so it is open any time the engine is running. You can check this easily by removing the vacuum hose from the top of it. There should only be vacuum when the heat lever is at the bottom and the engine is running.

Big blocks are hot, but did you bypass the heater core? If not the water valve in engine compartment may have failed. This assumes the vacuum controls are hooked up correctly under the dash. My 68 had AC, and my 70 big block car does too. I hate under dash projects due to all the AC stuff.

Probably not the heater hose valve. That valve only closes off the flow of water in the heater hose when the A/C is on. If the A/C is not on the water flows through the valve and through the heater core whether the heater is on or not . I suspect ether faulty vacuum or faulty duct function in the heater box.

Royce,I did not mention anything about a control in my post only the heater hose valve. If you think that the water valve on the heater hose is normally closed then you are misinformed .   The valve closes when vacuum is applied . It snaps back open when that vacuum stops. It is designed so that if the A/C is on the flow of hot water is stopped so that the heater core is not fighting the evaporator core.

Royce ,you are wrong . You obviously do not have a working valve to double check otherwise you would not make that incorrect observation. I on the other have refurbished used and NOS ones on hand to verify the correct normally open observation. It is easy enough to test by blowing through the nipple in the direction of the arrow marked on the valve . When you apply vacuum to the diaphragm the valve shuts off the flow.  Which I did test to confirm. I respectfully suggest you do the same . 

[Royce Peterson]

Bob,

Apologies - you are so right! I was on the road and got home tonight. It works exactly the opposite of what I thought I remembered. You are correct sir!

[Bob Gaines]

Bob,

Apologies - you are so right! I was on the road and got home tonight. It works exactly the opposite of what I thought I remembered. You are correct sir!

Thank you for the honorable apology . It is of course accepted.