When driving at highway speeds the A/C does not blow cold air

ANONYMOUS

MEMBER
2001 MITSUBISHI ECLIPSE
127,000 MILES

The heat blows cold air except for driving on the highway. As soon as I get off the highway it goes back to cold air. I then noticed a small puddle under the passenger side of the engine. The overflow was empty so I replaced some of the fluid. The fans are turning on and no visible leaks to any hoses. Yesterday I had a friend install a new thermostat and flush/bleed the radiator. He said the radiator should be getting hot and it's not. I picked up the car today and it still does not have heat and the temperature gauge will rise to hot and then level out several times while driving. I noticed antifreeze coming out the front of the car once I got home. Not a lot and the overflow was still full. Any ideas?

2 Replies

HOMER1967

MECHANIC
875 POSTS

You do need to pressurize the system to find the leak first, after that you need to bleed the system of air, you may have a restricion in the heater core or even a head gasket issue. But you have to fix the leak before you can go any further.

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Saturday, December 1st, 2012 AT 1:25 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

I'm a bit confused. The heading indicates the AC doesn't blow cold at highway speeds. In your post, you indicate there is no heat unless you are driving on the highway. Based on everything in your post, I suspect the problem is the heater. If that isn't correct, let me know.

First, there is a good chance the heater core is plugged. The first thing I need you to try is this. Here is a link that explains how to repair a heater not working. Take a look through it and see if it helps.

https://www.2carpros.com/articles/car-heater-not-working

As far as the coolant leak, it needs to be identified. I have a feeling we will find it is the water pump. On the pump is what is known as a weep hole. Check for evidence of a leak at that point. I attached a pic showing it.

Also, here are a couple links you may find helpful when checking for a leak:

https://www.2carpros.com/articles/car-is-leaking-coolant

https://www.2carpros.com/articles/radiator-pressure-test

The second link explains how to pressure test the system. It would be a good idea to do this if you can't locate the leak.

Last, a bad head gasket can cause the things you are experiencing. Here is a link that explains how to check if that is the issue:

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know what you find. Please feel free to ask me questions if you have them.

Take care,
Joe

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