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I have a 1998 Ford Escort with 113k miles. It's never given me any major problems before, except for the AC going out about 4 months ago (details to follow).

In the past week while driving with the AC on, I've noticed that the cold air stops blowing and becomes lukewarm. At the same time, I noticed that my engine temperature gauge is in the red. I took it to a reputable mechanic, they did an engine head test and a coolant pressure test, saw no issues, and couldn't reproduce the problem.

The problem has kept happening. Generally, I am driving at highway speeds with no problem. If I encounter traffic below 30mph, or switch to city driving, the car begins to overheat. If I notice the gauge in time, I can turn off the AC and sometimes it will return to a normal temp. (Though sometimes it will overheat even if the AC has not ever been on.) The car overheats to the degree that steam begins coming from under the hood in the vicinity of the coolant reservoir.

Back to the AC, when it broke a few months ago it was diagnosed as a bad relay in the CCRM. I replaced the original CCRM with a remanufactured one (made by BWD) from Advance Auto Parts. I'm wondering if this could have something to do with my current problem, since I think the CCRM does much more than run the AC.

Any advice is appreciated.

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    When you see this happening, you need to stop the car and check the lower radiator hose. Rev the engine a little and see if it collapses. You may have a weak (old) hose there, which allows the coolant pump to suck it close when it gets hot. – Pᴀᴜʟsᴛᴇʀ2 Oct 2 '15 at 0:16
  • Quick question: How would you check whether the lower radiator hose collapses while you rev the car? – Captain Kenpachi Oct 2 '15 at 9:47
  • rev it using the arm on the throttle body and watch the hose. You could also have someone else hit the gas while you watch. – rpmerf Oct 2 '15 at 11:45
  • Did you ever resolve this problem? I am having the exact same scenario. I believe it is the fan as it does not spin when I start the car. When I turn the AC on it will spin. But even if the AC is running (fan spinning) in the car will get hot after I have been driving a while in stop and go traffic. So aparently the speed the fan runs for the AC isn't sufficient to cool the coolant in the radiator. The schematic shows a high and low speed relay. I am trying to identify what is exactly the problem before I go and replace the CCRM again. – Brendan Oct 13 '16 at 2:52
  • It was the radiator fan, the CCRM failed and the fan wasn't turning on. If it wasn't driving at highway speeds, there wasn't enough airflow to cool the engine. I replaced the CCRM (again) and haven't had a problem with overheating or AC since. – John Oct 13 '16 at 6:03
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A non functioning radiator fan could have those symptoms. In your car the fan is most likely shared by both the radiator and AC. When driving there is sufficient air flowing across the condenser and radiator. When you slow down the fan should take over to keep the air flowing. If it's non functioning it could cause the AC to blow warm and may overheat.

Start the car, turn on the AC. The fan should run whenever the compressor is running.

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    Could also pull into a gas station when it starts to get hot to see if the fan is running or not. Check the fuse, relay, wiring, power at the fan, and you might want to try to jump the fan directly to the battery(with a fuse just in case) to see if the fan spins. – rpmerf Oct 2 '15 at 11:44
  • Many cars also have an overheating sensor on the compressor which will turn it off if it gets too hot. – Robert S. Barnes Oct 13 '16 at 5:09
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It's entirely possible that your engine is being air cooled just enough by the rushing air of highway speeds. When you slow down, or encounter stop-and-go traffic, the amount of air just isn't enough.

This could be because of a fan failure, as @vini_i mentioned, or it could be due to insufficient coolant flow -- either because the coolant is low, or because the water pump isn't doing its job.

The lowest hanging fruit is undoubtedly the radiator fan. If it isn't spinning, that's almost certainly your problem. If it is, does it seem like it's operating at full speed, or half-hearted? I've seen fans that appear to spin, but really aren't producing any air flow.

If the fan is in good shape, check coolant levels. If they are sufficient, you may be looking at a new water pump.

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