When I turn the car on the blower fan runs full blast but the air isnt cold - its about air temp. then after running about 3 mins. it gets cold.. I have the C68 auto HVAC and it isnt flashing or anything indicating low freon.. this doesnt sound good.. any ideas?

 

It is my understanding that the following is occuring;
- warm air is being passed over the evaporator
- at start up the above air is hot
- at start up the evaporator is hot
- at "max" the air is passing thru the evap quickly so it doesn't have much resident time to cool.
- all the above mean that it takes some time to cool down.

As long as it gets cold "enough" (40-45F at vent) within say 10 minutes, I'd say it is normal as our cars aren't the greatest at AC

I plan to get into the evaporator box and clean things out if need be as my system doesn't meet the "enough" criteria.
:cheers:

 

Same problem here - turn on AC and often hot air for 4 minutes. Sometimes it would even start to get cold then get hot.

I am working on my 1988 C68 aircon at the moment and have fixed many things. I've had enormous help from SunCR - he's the Aircon Guru so perhaps he'll come in and tell me I'm barking up the wrong tree, BUT -

I think I know why this happens.

Here's my theory -

Firstly some background - I started up a cold car last week to test my new blower motor. I have a digital thermometer reading to .1 of a degree accuracy, one sensor in the cabin and one in the air vent.

There was no cold air, both readouts were about the same - showing the cabin temp. The vent temp rose a little, picking up engine heat I think.

The compressor was going on for 5 seconds and off for about 20.

I'd fiddled around with so much stuff I thought I must have done some serious damage - like blown a hole in the evaporator or something.

Thanks to the forum I read that night that the aircon can't begin to work until air flows over the condensor. (I had not taken the car for a drive when testing - no seats)

The next day I disconnected a plug which then forces the fan to come on with ignition and started the engine - instant cold air - 51F in the vent in 3 minutes

So I reckon that when we re-start our engines from hot there's a lot of stored heat in the condensor etc and if there's no air blowing to cool it down we get sort of reversed heating.

Because I had digital temp readings of vent and cabin I could observe what was happening and because the car was cold I was not be confused by things getting hotter. I should mention that my heater is totally disconnected so when I get hot air in the cabin I know it's not a faulty door in the plenum/ fauly vacuum line/C68 gone crazy etc - there should be no heat.

Here's a pic of the plug I disconnected to force the fan on.http://www.users.bigpond.com/mphealey/CorvetteDream/ForumPics/Fanon.jpg

Now this theory makes perfect sense to me but I'm no expert on this. My solution to the hot air at start up will be to have a switch to turn the fan on when it happens.

My front fan never seems to run so I think I'll wire that one up.

S'nut

 

That sounds normal to me, it shouldnt be cold on startup unless the engine itself is cold. Even then, it would need to be cool outside.

Mine was cool this morning, it was like 91, but it did take 4-5 min to really get cold.