Has anyone upgraded the supply fan for heating and a/c system? First off my car is a 82 GSL. Let me start by saving that I upgraded the compressor, filter drier, condenser coil, expansion valve, had new refrigerant lines made and replaced the supply fan. My A/C do work but to me it seems that the fan that’s designed for 1st generation RX7 turns to slow for cooling. I feel that the fan is not moving enough air across the evaporator. When the system is in the A/C mode the fan needs to turn fast because cold air is heavier than hot air. If the fan was able to turn faster (more CFM) it could circulate the warmer air across the evaporator more efficiently. Which in turn will allow the car to cool quicker inside. If anyone has done this in the past please share your experience with this. This is coming from a guy that do Commercial Heating and Air Conditioning for a living.

 

The stock blower is plenty.

A more powerful blower will just cause warmer air to come from the vents. The evaporator and condensor are pretty small relative to the heat loads requested of them. A car A/C system is generally close the the same cooling requirements as a moderate sized house because cars have such worse insulation and window area. Car A/C is in the 25k-50k BTU range, the little tiny parts can only supply cold air with the fan speed on low.

 

Are you sure the resistor for the motor speed is working correctly? Do you have all the speeds working? Its the resistor pack that really controls the speed. You could try modifying to values to get higher speeds.

 

That's not really fully what is going on. The lowest blower speeds do go through the resistor block, but high speed is always a direct 12v to the blower, bypassing the resistor.
I'm not sure if this is an intentional fault-tolerance or a happy coincidence, but when the resistor block fails, you still will have blower capability although only on high speed.

All that said, these ARE cars getting on 50 years old, and as someone getting close to 50 years old myself... well, things get leaky with age and wind can escape where you wish it wouldn't. Specifically, the foam that seals the ducts breaks down and can cause air leaks, so more cold air flows out behind the dash instead of through the vents.
I also can't stress enough how important all the different seals between the transmission and shift lever are. They crumbled and cracked and the big foam pad under the shift boot usually gets discarded... all that is important to keep exhaust heat from getting into the cabin, and that makes the A/C have to work less hard.

 

True about the fan. I replaced my resistor pack with a Ford one that was almost a direct replacement a few years ago when I lost the low speeds.

Wait until you hit 65, then things really get interesting.

 

Back to the point at hand, it's very likely the fan motor has a lot of revolutions on it, and corrosion or wear on the motor brushes will definitely slow things down. As others have said, straight 12v goes to the fan on HIGH speed, so you could pull the motor assembly out the bottom, exposing the squirrel cage assembly, rig a connector to 12v and then run it free of the enclosure to see if it's poor motor performance. There are 3×10mm bolts holding the motor onto the enclosure, easily accessible from the passenger footwell area.

If the motor has gone bad, you could either replace with a newer assembly or try to take it apart and fix the brush issue, but you'd need to know something about DC motors and how they work. Alternately, you could run down to your local pick-a-part and see if they have any motor assembly that's close in size that you could mount to your assembly, but it would need to have the same shaft diameter to fit the squirrel cage.

In my experience working with older cars, corrosion in the wiring, connectors, and sometimes the motors themselves can be corrected with new wire runs, or possibly some spray electrical contact cleaner - but don't set expectations that it will blow as hard as a new car. These cars never had wonderful A/C, but they did work effectively even out here in the desert.

 

Yes, everything works. I just feel that the volume of air coming out the air vents are weak. The speed which the air moves across the evaporator makes a big difference when it comes to cooling. Even if your evaporator is super cold and the fan is not moving enough air across it, the car isn’t going to cool properly.

 

As I stated earlier, everything dealing with my air conditioner is new except the evaporator itself. I also cleaned it when I had everything out of the car. The fan motor was replaced twice because I thought something was wrong with the 1st one.

 

This may sound like a dumb question, but could you have the blower wired backwards?

I ran into this with an aftermarket blower for a Honda once. It was wired backwards. It still blew air through the vents but at markedly lower volume.

I still reiterate that higher speed from the blower makes for warmer air from the vent. There's only so many BTU that the evaporator can transfer and a higher speed distributes that among more air, resulting in a lower temperature drop. The difference in output temperature can be 20 degrees, blowing 40F on low speed and 60F on high.

 

At the same time, if the blower is not moving fast enough you will not get the proper heat to air exchange across the evaporator. I been doing heating and air conditioning for over 20yrs and this do make a huge difference. Also, my blower is turning in the right direction.

 

Automotive HVAC is different from building HVAC, and a lot of the principles from one do not translate to the other. The compressor doesn't run at a fixed speed, for starters, so the system accommodates this. The volume of air in the cabin is also a lot smaller yet also much more poorly insulated and with much more sunload. A car can be thought of as a shed sized greenhouse, and we want to try to make it comfortable inside when it is 90 degrees and sunny.

 

I'd be tempted to throw a thermocouple onto the evaporator and log temperatures depending on the blower speed and see if you're wrenching out as much efficiency as you possibly can.

 

Technically there IS one, sort of. The compressor is controlled by a high pressure switch in the liquid line under the hood and a temperature switch in the evaporator. If the compressor cycles off, the evaporator is getting down to the range where the condensation can start to freeze, and that's all you can ever cool down to. What generally happens with higher blower speeds is that you overrun the ability for the compressor to move enough refrigerant and the evaporator to reject heat. In these pre variable compressor cars, the compressor gets sized large enough to somewhat work at idle without feeling like you're being pulled backwards when it kicks on at highway speeds. Condensor size and airflow is also important and our cars have pretty crappy condensors, compared to modern ultra high efficiency units. Our condensor is basically just a big S tube with some fins here and there. One of my ideas is to use a modern condensor with their micro tubes, get better cooling with technology instead of sheer size.

The neat thing is, because the evaporator switch measures temperature and not pressure, you don't have to adjust it when switching from R12 to R134a. But, yes the temp switch IS adjustable. Right pain to access, but it's adjustable.