The heat is rising while it’s stopped the car and the engine working

Hi Salah,

It sounds as though your cooling system is marginal; it's operating fine for normal operation but when you add the extra stress of the air conditioning, then it gets overwhelmed and can't keep up. The A/C has what basically amounts to another radiator that's normally mounted in front of your cooling system radiator so when the A/C is on, that radiator adds heat to the cooling system. At this point it sounds like your cooling system can't handle that extra heat, so the problem will be in determining the problem with the cooling system.

The cooling system starts with the water pump. That pump moves the antifreeze through the engine block where it picks up heat from the engine, then pumps it to the radiator, where either fans or moving air will pick up the heat and take it away from the car. Here, in no particular order, are a few things that I've run into over the years that caused cooling system problems in my cars.

1. Stuck thermostat. The thermostat regulates the temperature of the water in the engine to keep it at the optimum operating temperature. It can be stuck open or closed, which can result in different kinds of problems. Testing it usually involves removing it from the car and placing it in a pot of water on the stove. Heat the water and watch the temperature with a thermometer. When it reaches its operating temperature, the thermostat valve will open; if it fails to move at that point it would be considered bad and should be replaced.
2. Clogged radiator. Over time corrosion can build up inside the radiator and choke off the narrow water passages, resulting in reduced cooling capacity. Professional testing can be done by a radiator shop, but you can get an idea if there's a significant problem by running the car until it's warmed up to operating temperature. Shut the car off, then carefully feel the temperature of the radiator over the entire surface. If there is a blockage you'll find areas that are still cold vs. being hot like the whole thing should be. If that's the case you'll need to replace the radiator. While you're checking, make sure the exterior of the radiator surface is clean of debris or dirt that could be keeping air from flowing through it.
3. Failing water pump. If the pump is failing it won't be pumping a sufficient quantity of water and therefore won't cool the engine well enough. Generally manufacturers provide what's called a "weep hole" in the lower part of the pump where radiator fluid will leak out when the bearing and/or seals on the water pump have failed. Coolant coming out of the weep hole is an indication you will need to replace the water pump. Note that in modern front wheel drive cars, the water pump is notoriously difficult to access, usually being under a timing belt cover, so it may be hard to tell if it's leaking or not without removing the timing cover.
4. Kinked radiator hoses. The hoses connecting the radiator to the engine block can get bent and kinked, reducing the flow of water through them. If that's happened you may be able to straighten them out by relocating the mounting points or disconnecting and straightening them out. Otherwise you may need to replace the kinked hose if it won't stay straight.
5. Failed radiator fan. If your radiator only has one fan, then this probably isn't the problem, as it would overheat whether the A/C was on or not. However, many cars have two fans, and if one of them has failed but the other is working, that may be sufficient to cool the car under normal circumstances but not with the A/C running. Generally you can tell if they're working simply by turning on the A/C; both fans should then be running; if not you may need to replace the fan or check the wiring.
6. Blown head gasket. If the head gasket on your engine fails, it can allow exhaust gasses to pass directly into the cooling system, overwhelming it's ability to cool the motor. This is an unusual situation and doesn't happen all that often, so save this possibility for last. There are kits called block check kits you can use to check for the presence of hydrocarbons in your radiator if you suspect a blown head gasket.

Those are the main possibilities I've experienced over the course of several decades of working on cars. The problem of yours could be as simple as replacing a thermostat or as complicated as a blown head gasket; there's no way to tell without working through a diagnostic procedure.

Good luck; check out the things I've mentioned, then be sure to come on back and let us know how it all turns out; your experience could well help someone else with the same problem some time down the road.