Engine dose not overheat but heater only blows cold air. I manuly opened the heater control valve and get hot air only in front not in back but only with engine reved up. No heat at idle.

Start with the coolant level in the radiator.
Although the car may not ever run hot, the heater is higher than the water pump, and any air caught in the cooling system can cause the heater to stop working.
Your cooling system should be full of coolant.
Next, the thermostat of the engine could be stuck in the open position, which will not allow the heater to put out warm air.
If you car has a dash gauge that reads the engine temperature (I do not think it does), you can tell if the thermostat is stuck open by the fact the gauge stays cold, or nearly cold, all the time.
Finally, the valve under the hood that opens or closes to allow the hot coolant to flow from the engine to the heater may not be opening and closing properly. Most of these valves are vacuum controlled from the dashboard controls.
God bless your efforts.

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.------
Engine Overheats and heater blowing cold?http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html
---------Heat blows cold on drivers side and hot on passenger side?http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html
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This will help.Thanks.

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

------
Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

---------
Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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For car running hot and overheating issues, I suggest to you go through this help links. Click this link below and go through the troubleshooting procedure to take care of the problems: ----Car runs hot? http://howtobyme.blogspot.com/2011/11/car-runs-hot-in-traffic.html
-----------All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html
Car freeze overnight and started overheating while driving?http://technoanswers.blogspot.com/2012/01/car-freeze-overnight-and-started.html-----------Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

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Car overheats and Air blows hot at idle?
http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html
--------overheating? http://schematicsdiagram.blogspot.com/2011/12/buick-century-overheating.html
----------Car engine Overheats and transmission starts slipping?http://schematicsdiagram.blogspot.com/2011/12/car-engine-overheats-and-transmission.html
----------This details will help.Thanks.

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

------
Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

---------
Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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This will help.Thanks.

For this types of problem,i suggest you to check this help links:----Car heater blowing warm, but not hot air?http://schematicsdiagram.blogspot.com/2011/12/car-heater-blowing-warm-but-not-hot-air.html
---------A/C, heater, defroster fan, not working?http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html
--------Heater problem?http://technoanswers.blogspot.in/2012/02/heater-problem-on-isuzu-trooper.html
---------Engine Overheats and heater blowing cold?http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html
-----------Heat blows cold on drivers side and hot on passenger side?http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html----------------This will help.Thanks.

I would look for a vacum leak on the control valve for the heater. There are 2 lines from the radiator leading back to the firewall. One has a control valve on it that should be vacum controlled. When you back flushed to the heater core you may have forced this valve open temporarily. The control may have low vacum or insufficient vacum to open a stuck valve. The good news is you can actually manually open this valve and tie it in the open position which will at least temporarily solve the problem. Check your vacum lines for leaks and check the valve to make sure it isn't sticking.

Heater control valve malfunction will not cause engine to overheat unless coolant is leaking externally...Overheating going down the road can be the result of a few different things...Partly clogged radiator...Insufficient air flow due to possible fan problem...External coolant leak...Make sure fans are operting properly and have cooling system pressure tested for leaks...Gaining and losing heat on the inside of the vehicle usually means system is low on coolant but you must find out where coolant is going

There should be a heater control valve located under the hood in a hose. One hose goes into the firewall which flows through the heater core inside the rear of the dash and another hose coming out and back to the engine. It is probably a bad control valve or maybe the cable is stuck which opens and closes it when you move the knob on the dash. Have someone inside the car move the lever from hot to cold and see if the cable to the heater control valve moves. The rest depends on how handy you are. Should be an easy repair for your local shop.

I expect the controls or valve to open coolant from the engine will not open. As it is not open it does not allow the hot engine coolant to flow thru the heater coil. I am uncertain with your H1 if this valve operates via a control cable or vacuum.
I hope this may have helped,
Tom

Ok it may be that the heater core bypass valve isnt opening. All that valve dose is when you turn the climate control to heat it opens a valve that allows hot coolant from the engine to flow through the heater core. What I would do is check that. It will be on the left side (passange) of your engine bay.You will see two black coolant hoses next to eachother and one will have a black box with a wire that runs to it. Have someone move the climate control from hot to cold to hot back to cold. If you dont see the wire move then you can move it yourself to open the valve.

Let me know if the valve opens or not using the climate control.