1992 A/C Blower Fan does not come on after parking car for an hour or so.

[Full Octane]

I have a 1992 and the CCU has been rebuilt in the past 2 years so I am not suspect of it being an issue.

The issue I am having now is when I first start the car and drive it, all A/C functions work fine. I can get different fan speeds and temps or I can put it in full auto and it works great.

When I stop at a cruise in for an hour or so then get back in the car (90 plus degrees but I have left the windows open) everything seems to work fine except the blower. I can hear the change from fresh to recirculate when I change it, the compressor kicks in and fresh air flows through the vents while driving. Sometimes after driving the car for 15 or 20 mins the fan will magically start blowing for now specific reason and all functions work again.

This does not happen every time, sometimes it works for 3 or 4 days then it starts acting up intermittently.

I have the big shop manual, thoughts on where to start or does this sound like a problem someone else has had.

I have done some searches and a few came close but not the same issue.

Thanks, Curt

 

[Old Guy]

You could have an intermittent electrical connection failure caused by thermal expansion at elevated temperatures. The first thing to do would be to confirm that the problem is not exclusive to the power transistor which sits in the blower housing. After the blower has stopped operating, turn the CCU on and switch the fan speed to maximum (manual setting). This by-passes the power transistor completely.

If the blower starts to operate on the maximum speed setting then you likely have a thermally sensitive connection at the Blower Hi Relay or the Power transistor. It is also possible that the power transistor is overheating if it has accumulated 27 years of crud on its cooling fins. So, remove the relay and check operation and look for damage on the connections. Remove the transistor and check connections and clean heat sink if required.

If switching the fan speed to maximum on manual does not force the blower to operate, then you could have a thermal sensitive problem with the Blower Relay (which is different than the Blower Hi Relay) or with the blower motor itself. You can remove the relay to check its operation and look for signs of damage on the connections. Checking the operation of the blower motor is trickier. Since the problem appears to be thermal sensitivity, removing the blower and testing is likely going to show no problem if the motor cools down. When the blower has failed, you need to arrange a quick test where you can apply 12 volts directly to the blower motor while things are hot. If the blower operates, the problem is someplace else. If the blower does not operate, then let it cool and re apply 12 volts directly to the motor. If the blower runs then you know the problem is with the motor. If the blower motor turns out to be faulty, it may just be worn brushes (the car is 27 years old). Rather than a complete new blower motor, it may be possible to just replace the brushes. Check out this thread for some guidance

http://www.nsxprime.com/forum/showthread.php/208341-AC-Condenser-fan-rebuild

Testing the relays suffers from the same cool down problem (it may test good once it is out of the car). One way around this is to do a relay swap with one of the other single pole single throw relays in the car to see if the problem follows the relay).

These are not the only possible causes of the problem; but, its where I would start.

Where to start in the shop manual depends on which version of the shop manual you have. In the initial 1991/92 shop manual page 20 at the very end of the electrical section (section 23) shows the complete wiring diagram for the CCU and blower stuff. However, the blower test procedures start on page 22-40.

 

[Full Octane]

Thanks for the response, when this happens the fan will never some on even if I put it on high.

Question can either the blower hi or blower relay on their own stop all fan operations? I was thinking if one of the relays was bad it would either work on high or another speed.

I will try some of the other steps.

 

[Old Guy]

The Blower Hi Relay only functions when the fan is switched to its maximum speed, so a Blower Hi Relay failure will not cause non operation at speeds below maximum. A problem with the Blower Relay will prevent operation on any speed. A problem with the power transistor will prevent operation on any speed below maximum. Mix and match :smile:!

 

[Sh00ter]

Try swapping your blower relay with the horn relay.

 

[Full Octane]

Thanks! The relays seem pretty cheap, think I will pick up two and do a swap to see if the issue goes away.