99 civic EX - AC on and the heat gauge goes up
 

Hi there,

Wondering if anyone can confirm my diagnosis of my sister's car, 99 civic EX
175000kms automatic.

Driving with AC on, the heat gauge will suddenly start to go up. Usually
sits around 1/2, it goes up to about 3/4. The AC stops working. They turn
off the AC, heat comes down.

Just not entirely sure why the AC has anything to do with engine temp since
the condenser and rad are separate? Belts are good, but here is a weird one:

She checked the radiator level once it cooled off, and the fins were showing,
it looked as though the rad was low. There was still coolant, and it wasn't
overheated according to the gauge, so she proceeded to the local autoparts
store to get some premix antifreeze. Once she got there, bought the
antifreeze and came outside to fill up the rad, it was full!

My diagnosis is as follows:

1. Bad thermostat - probably needs to be replaced anyways, the car has
175000kms on it.

2. Bad fan switch on rad - if the fan doesn't kick in, and the AC is
creating more heat when its on, it could contribute to overall engine temp
increase.

3. Plugged rad fins - we live in Manitoba, lotsa bugs! so maybe the rad
fins need to be carefully cleaned out to allow for better heat transfer
efficiency.

Any other ideas? The timing belt was done recently, but the water pump was
left alone. I did suggest they replace it, but they didn't I guess it could
be the water pump too.

Any input would be great!

t

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