Mehran is a small and poorly designed car that has a historic problem when it comes to ACs. Typically the AC doesn't quite work well and for old cars, the Car ends up heating up.
General Causes of heat up
There are a number of reasons why cars, specially old ones heat up. Problems may be one or more of the following:
- Engine needs to be overhauled
- Begin needs to be changed
- Clutch plate needs to be changed
- Radiator needs to be serviced or cleaned
- The radiator cap needs to be changed (YES THIS IS QUITE IMPORTANT). The spring in the radiator cap is very important. When the water steams up, it pushes part of a cap up and water is allowed to circulate. If your cap is damaged, your car will heat up)
These are causes of car heat up if one or more things are wrong with the car. Obviously, you will need to get your car checked for any of the above mentioned problems to get the car fixed.
REMEMBER, a few days before you take your radiator to be cleaned, poor in some anti scale and anti rust water treatment chemical in it and let it run for a couple of days. This would remove any kind of scale that is hindering the heat exchange. After the radiator is cleaned MAKE SURE TO PUT ONLY FILTERED WATER in the radiator, as poor quality water leads to severe scaling of the radiator.
Mehran AC Design Flaw
Another reason why ACs cause heatup in Mehran is a design flaw, namely the fact that the Radiator and AC Condensor are stacked one on top of the other. What does that mean?
Water flows in pipes through the engine and absorbs the heat. The hot water comes to the radiator, and passes through thin capilaries covered by the fins of the radiator grill. The air passing through the radiator grill, cooling the water. The cooled down water goes back into the engine. This process goes in a cylce, keeping the engine cool. You have a fan installed behind the radiator grill that SUCKS the air in, to help the process.
SO ... the radiator has to be COOLER if any kind of heat exchange is to take place.
The problem is that the AC condensor, which is the RADIATOR of the AC is placed DIRECTLY UNDERNEATH the radiator. The AC works on the same principle of heat exchange, but, basically, the AC gas needs to get cooled. When the AC gas passes through the AC condensor, it tries to loose its heat. This HEAT, heats up the RADIATOR, which is unable to cool the water. So, as only hot water keeps going back into the engine, the engine gets progressively hotter, until you come to a point where you turn off your AC, stop the car and poor water out of the bottles you have stacked under your seat.
There are a number of things you can do to solve this problem
Replace the radiator fan with a bigger fan (I put in a corolla fan) with a relay.
Put a similar fan, with slight modifications to the bumper infront of the AC Condensor
If you are adventurous, you can get a slight modification done where you can shift the condensor slightly inside, so the condensor is not EXACTLY under the radiator. In this way, you can easily put the fan on the outside without modifying the bumper
Make sure your gas is full and radiator is in good working order.
There are a number of other solutions I have seen. The people who did these changes say they work but I haven't actually tried them myself.
One friend of mine has installed another water bottle (exactly like the one for windscreen wipers). He installed the complete system from an old mehran and placed the two water jets so that they point towards the radiator. According to him, whenever his temprature meter starts going up, he presses a button and it sprays the radiator with water, cooling it for a while.
Another friend of mine has a Carrier installed on top of his car. He welded a large sheet of metal (painted white) on top of it It is as wide as the car and slightly larger than the length of the roof. It looks very strange but is like the car is always in the shade. And it DOES work really well. In fact, waiting on traffic signals is much much painfree, as you are always under a shade. It is a very innovative and practical solution .... if you dont mind the goofy looks of your car (and of course, slightly compromised aerodynamics).
Always try to use shades for your windows. By personal experience, your AC performance would go up significantly.
Hope this helps