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timgtndrty
08-19-2013, 05:54 PM
Been working on a 01 Geo Prism with the vvt-i 16 valve 4 cyl. 160k+ miles.

It's been overheating. Here's what we've done so far

Replaced:
Water pump
Thermostat
Coolant flush
Radiator cap

Checked the fans (turned the AC on and off) both fans come on seem to be working.

Still runs hot at freeway speeds unless you turn off the AC.
Thinking we should see if the radiator is clogged or change it out if it's not too many donuts.

Any other advice welcome.

Thanks.

timgtndrty
08-20-2013, 01:53 AM
Found this article so re-testing fans to see if they are running at full speed or low speed.


Re: 2001 Chevy Prizm A/C Problem
Reply #6 on: June 15, 2007, 05:15:22 PM


The condenser sits infront of the radiator and does look like a radiator. Spray the condenser with water using your garden hose with the ac running. See if the pressure drops and the air gets cold in the car. If it does, then you have a heat transfer problem. If it is a heat transfer problem, then there is a possibility that the coolant fan that isn't running is causing the problem. Here is some info on the fans and their operation:

Coolant fan control
The main and auxiliary fan motors run at half speed in series configuration when all of the following conditions occur:

The A/C system is operating.
The A/C system pressure is below 1226 kPa (178 psi).<<this is the high side pressure
The ECT (Engine Coolant Temperature) is below 83C (181F).
The main and auxiliary fan motors run at full speed in parallel configuration when either of the following conditions occur:

The ECT reaches 93C (199F).
The A/C system pressure exceeds 1520 kPa (220 psi).
The engine cooling fan system consists of two electric cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage on two individual power circuits, from fuse and relay block 1 and from junction block 2. The ground path is provided at G103 and G104.

During low speed operation, which is when the A/C is operating and the engine coolant temperature (ECT) is below 83C (181F), the PCM supplies the ground path for the fan 1 and the fan 2 relays through the cooling fan relay control circuit. This energizes both relays, opens the fan 1 relay contacts and switches contacts in the fan 2 relay. The engine main relay supplies battery positive voltage through the cooling fan motor supply voltage circuit to the auxiliary fan motor. When the A/C is operating, the compressor clutch (MG) relay energizes the fan 3 relay. The ground path for the auxiliary fan motor is through the switched contacts in the fan 2 relay, through the closed contacts of the fan 3 relay and through the main fan motor to G103. The result is a series circuit with both fans running at low speed.

During high speed operation, which is when the ECT reaches 93C (199F) or the A/C system pressure exceeds 1520 kPa (220 psi), the PCM removes the ground for the fan 1 and the fan 2 relays through the cooling fan relay control circuit. This de-energizes the fan 2 relay which switches the relay contacts and provides a ground path for the auxiliary fan motor at G104. At the same time, the fan 1 relay is de-energized closing the relay contacts and providing battery positive voltage on the main fan motor supply voltage circuit to the main fan motor. During high speed fan operation, both engine cooling fans have their own power and ground path. The result is a parallel circuit with both fans running at high speed.

The A/C high pressure switch is in series with the PCM controlled ground for the coils of the fan 1 and fan 2 relays. If the A/C system pressure exceeds 1520 kPa (220 psi), the pressure switch opens the ground circuit to the coils of the fan 1 and 2 relays. This has the same effect as if the PCM had removed the ground for the relays.

The PCM will control the ground for the fan relays based on input from the ECT sensor in order to maintain the cooling system at normal operating temperature.
Last Edit: December 31, 1969, 06:00:00 PM by discretesignals
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