Electric Air Conditioning (AC) System

[ericjon262]

anyone know the approximate thermal power (BTU) of the stock A/c system?

[Emc209i]

Why?

[Shaun41178(2)]

because reasons. LOL

[Emc209i]

He planning to use one as an intercooler?

[ericjon262]

no, I am exploring alternate options for a/c on my car.

[Series8217]

The Fiero A/C is extremely overpowered. It's the system for a full size sedan. What do you want to do?

[The Dark Side of Will]

The Fiero A/C is extremely overpowered. It's the system for a full size sedan. What do you want to do?

I asked about this on Old Europe not too long ago... looking for R134 compatible condensers. Corvettes and 4th Gen F-bodies both have more condenser area than Fieros.

Also, a Fiero with a sunroof has a VERY large solar heat load for the volume of the cabin.

[ericjon262]

The Fiero A/C is extremely overpowered. It's the system for a full size sedan. What do you want to do?

I'm looking into 12 volt compressors and completely removing the engine mounted compressor and lines to/from.

The Fiero A/C is extremely overpowered. It's the system for a full size sedan. What do you want to do?

I asked about this on Old Europe not too long ago... looking for R134 compatible condensers. Corvettes and 4th Gen F-bodies both have more condenser area than Fieros.

Also, a Fiero with a sunroof has a VERY large solar heat load for the volume of the cabin.

typically, R134a systems use larger and more efficient design condensers than R12 systems, to attempt to maintain the same thermal power as a R12 system

[Series8217]

An electric AC compressor would be nice since you could shift weight to the front and eliminate a lot of lines and connections.

I haven't had any cooling issues with my R134 retrofitted Fiero using an R134 compressor. I don't have a sunroof in my car though.

[Emc209i]

My kid brother had a Fiero with an HR6 compressor pumping R134. There was a sunroof and no difficulty cooling the inside on a 90*F day. As long as you're not using an HR6 or DA6 compressor you should be fine with the small surface area of the stock condenser Will. However, I too had replacing the stock condenser with a double stack or triple stack at the back of my mind. Just for the sheer hell of overbuilding the system.

[ericjon262]

could have to do with the compressor, but it's most likely the fact that the size of the fiero's cabin is so small that even with an ok system, it cools well.

[The Dark Side of Will]

I'm a big guy in a small cockpit and I like it really cold when I drive, so I'm probably more sensitive than most to A/C capacity.

However, I also need to get some insulation back on my firewall and do some figuring about the Northstar compressor with the Fiero A/C, variable orifice valve and R134.

typically, R134a systems use larger and more efficient design condensers than R12 systems, to attempt to maintain the same thermal power as a R12 system

Conversely, an R12 system converted to R134 has an underperforming condenser...

[ericjon262]

]

typically, R134a systems use larger and more efficient design condensers than R12 systems, to attempt to maintain the same thermal power as a R12 system

Conversely, an R12 system converted to R134 has an underperforming condenser...

true.

another option that may work, would be to run a smaller orifice, this would reduce flow through the system, allowing the refrigerant to spend more time in the condenser, as well as increase the pressure drop.

[The Dark Side of Will]

That's kind of what a variable orifice valve does... It changes the orifice based on pressure difference... it actually bigger at lower pressures. This increases compressor duty cycle at low RPM, but also increases the mass flow of refrigerant through the evaporator. At lower pressures the temperature drop isn't as great, but the greater mass flow improves system performance by limiting the reduction in BTU's the system experiences at idle.

[ericjon262]

That's kind of what a variable orifice valve does... It changes the orifice based on pressure difference... it actually bigger at lower pressures. This increases compressor duty cycle at low RPM, but also increases the mass flow of refrigerant through the evaporator. At lower pressures the temperature drop isn't as great, but the greater mass flow improves system performance by limiting the reduction in BTU's the system experiences at idle.

that makes sense, the higher flow rate would keep the evaporator cold.

[Series8217]

What's the point in a variable orifice valve if you're using a variable displacement compressor?

[The Dark Side of Will]

There isn't, but I'm not.

[Series8217]

Huh. I figured the Cadillac Northstar would use a variable displacement compressor, since even my base model '88 Fiero did...

[The Dark Side of Will]

The variable displacement compressor was used apparently because the idle fluctuated too much on the 4 cylinder when the constant displacement compressor cycled.

GM uses constant displacement compressors on every engine & control system big enough to deal with the cycling. It's one of those weird circumstances where the "better" component is used on the cheaper car.

I don't know if variable displacement + fixed orifice would give better performance at idle than a cycling compressor + VOV or not... It may be a question of the range of variable displacement. If it can move enough freon to keep the pressure high at low RPM, then it might do fine with the fixed orifice... If its max displacement isn't enough, then a VOV probably won't help because compressor is already running at 100% duty cycle, so there's no performance headroom.

[Series8217]

The variable displacement compressor was used apparently because the idle fluctuated too much on the 4 cylinder when the constant displacement compressor cycled.

GM uses constant displacement compressors on every engine & control system big enough to deal with the cycling. It's one of those weird circumstances where the "better" component is used on the cheaper car.

You sure about that? The 1995 3.4 DOHC V6 compressor I'm using now is also variable displacement like the '88 Fiero 4-cyl compressor. Other vehicles that use the variable displacement compressors include LS1 F-body cars, all C5 and C6 Corvettes, and a lot of trucks..