Im trying to fix the hack job the PO done to my wiring harness. Winter is almost over and Im wanting to get the A/C up and working. I have all of the wiring diagrams, but I dont know what pressure switch is what. For a 90 RS camaro the diagrams only show one switch between the cycling switch and the clutch.

This is the "pressure cycling switch" that is mentioned on wiring diagrams right?




What about these two switches? Are both of these high pressure switches? (I know the clutch connector)


Thanks

 

1st picture.....You have the accumulator (silver cylinder) that goes into the evaporator (with the black cover by the firewall).

Accumulator has the "low pressure cycle switch" attached to it. You have it correct in your picture. If you take the rubber boot off it, you will see two metal prongs. In between those prongs is a small screw. 1/4 turn left is aprox 4 psi lower difference. You normally shouldn't need to adjust this. Although people who convert from R-12 to R-134a will often turn their low cycle switch down a few psi (from the stock 26 psi down to 22 psi for example). This is due to R-134a being a less efficient refrigerant. And it runs warmer at the same given psi that R-12 would be at. So 22 psi with R-134a is like 26 psi with R-12.

The little cap'ed line in the 1st picture is the high side port (high pressure....don't ever try to inject refrigerant in here when the engine is running. It will blow up in your face). Unscrewing the cap, there will be a schraeder valve in there....The low side port is the big schraeder valve that is on the front of the accumulator. That's the one you'd use for most A/C work.



2nd picture.....The connection at the bottom of the picture by the strut mount is your "high pressure fan switch." This is what turns the radiator fan on at 233 psi. (I'm assuming you have dual fans. If so, this will turn the passenger fan on when the pressure goes above 233 psi and off when the pressure goes below 190 psi.)

The high pressure cutout switch sits on the back of the compressor. It will off the compressor if the pressure gets up around 420 psi. Pictures of them are on ACKITS.com. Your high pressure cutout is right underneath where that 2 wires cut piece is on the back of your compressor.

 

http://www.thirdgen.org/techboard/co...-diagrams.html

This might help.

 

That is EXACTLY what I was needing to know. Thanks a ton!

I only have a single fan. My car is a frankenstein. The A/C system is from a 90RS. So that switch is normally open and closes at 233. I can figure out how to get that working with my fan.

Next question though, what does the pressure cycling switch do? Does it open during a range of pressures or only above/below a set pressure?

Im trying to figure out how the controls works, not just how to wire. I want to understand what Im doing. Thanks!

 

The system varies depending on single fan vs dual fan setup.

Single fan setup: Radiator fan comes on under one of two situations.

1) When the coolant temp has reached the point that the computer chip has deemed it's time to come on. Stock, that's 223°F. Many aftermarket chips (Hypertech thermomaster for example) will turn that on lower. The thermomaster turns it on at 177°.

2) When the air conditioning is turned on (or defrost is turned on), the fan will turn on.


Dual fan cars are a bit more elaborate. The primary fan is the driver side. The secondary fan is the passenger side.

The primary fan turns on exactly the same as a single car setup. Either by coolant temp reaching the computer chip's programmed point. Or when the A/C is turned on.

The secondary (passenger side) fan turns on under either of the situations below:

1) When the coolant temp has reached the temp that the "fan temp switch" in the passenger cylinder head between the #6 and #8 sparkplugs is set to turn on. Stock this is 235°F. Aftermarket fan switches generally have the option of turning on your fans in the 200 to 180° range. Two common fan switches are the hypertech 4026 and 4028. The 4026 is on/off at 177/166° while the 4028 is on/off at 200/185°......I personally run the 200/185° fan switch in my 89 GTA.

2) When the high side pressure reaches 233 psi, the secondary fan will turn on. Once it drops to 190 psi, it turns off.

Now the 190-233 psi range isn't constant if you open the hood and watch the fans. NC in the summertime as well as FL, TX, AZ etc, the high side pressure will probably never get down to 190 psi. Consequently, the secondary fan will be on constantly with the A/C running. Now if you turn on the A/C on a mild low humidity day where the outdoor temp is 70°, you might see the passenger fan cycle off every 30 seconds for maybe 10 seconds and then cycle back on.

How much refrigerant you have in the system also will effect the high side pressure. If you're low on refrigerant, the high side pressure may not get high enough to turn on the passenger fan. If it's overcharged, it may never turn off. Generally though if you're within spec, the turning on and off of the fan is mostly determined by outdoor temp and humidity.


Low pressure cycling switch.....There are two common types of A/C compressors. These are "cycling" compressors and "variable displacement" compressors.

Cycling compressors are the most common. These run for awhile and then shut off. Then run for awhile. The cycling is hard on them over time. Cycling compressors run until about 26 psi. Once it gets down to 26 psi, the compressor shuts off and doesn't come back on again until about 45 psi. At that point it tries to get back down to 26 psi. On a hot summer day when it's 100° outside, it may never get down to 26 psi. Thus the compressor runs non stop. So the low pressure cycle switch controls when to shut the compressor off. If you didn't have one or you had it set to let's say 10 psi, you'd have one giant block of ice in your evaporator and all over your accumulator as well as the line running from the accumulator to the compressor. Airflow would be reduced to nearly nothing as it can't get around the ice. The most common cycling compressor for 90 Camaros would be the R4.

Variable displacement compressors don't cycle. But rather change the piston stroke inside the compressor. They run full stroke until the point that they reach 28 psi. At that point they reduce the stroke just enough to maintain 28 psi. Easier on the system as they don't cycle. If it gets hotter outside or you get stuck in traffic, the stroke extends and you get more compressor performance.

So a cycling compressor runs full blast until it shuts off....then it runs full bast. A variable displacement compressor runs full blast until it reaches what would normally be a cycle off point (low psi) and then it reduces it's output but stays running. The most common compressor for GM in this regard is the V5.

An excellent example of the low pressure cycle switch in action is the use of defrost in the wintertime. If it's 40° outside or warmer, the compressor will turn on with the defrost. If it's in the 30's or colder outside, the compressor will stay off.....This actually has nothing to do with temperature or outdoor temps and everything to do with pressure. At 40°F outdoor temps, the refrigerant will be below the low cycle point. And it won't ever get to the 45 psi or so that it takes to actually turn the compressor on.

Now when you walk out to your car in the summertime, the low and high side pressures will be the same. Maybe 100 psi. Once you turn on the A/C, the low side wants to head down to 30 psi while the high side may shoot up to 250 psi (or even 300 psi in gridlock traffic). So essentially low pressure (evaporator, accumulator) is cold while high pressure (condenser out by the radiator) is hot.

Most people never think of it this way, but A/C doesn't actually create cold air. It's simply moving the hot air to somewhere else (the condenser). It's the same way with your fridge and freezer at home. They're not creating cold air. They're simply removing the heat from the air and sending it to the condenser (typically beneath your fridge). This is why there is a fan blowing hot air at your feet when your fridge is running.

If you have one radiator fan on your car but a system from a dual fan car, I would suspect that the fan pressure switch wouldn't even need to be hooked up. Since the radiator fan would be controlled by the coolant temperature or the computer chip sensing that the A/C is turned on.

 

That is everything I wanted to know! Thanks!

Hopefully I can get it working this evening.

 

Well I got it all wired up. Started it up, everything seemed to be working right. Accumulator got cold. Compressor started getting hot. Then alittle too hot for my liking. Engine ran less than a minute be the compressor was so hot you couldnt hardly touch it. So I unplugged it. Not sure what the problem is.

Oh well, atleast I got the wiring straightened out.

 

Hmm, I've never actually checked the temperature of the compressor itself. Always too nervous to get my hand caught in the belt.

I'll check mine with the laser temp gun next time I'm out.

 

This just felt way too hot for comfort. But I would definately appreciate you checking.

 

Well today when I got home from work I hooked it back up. I let it run alittle while and the compressor never got as hot as I thought it was getting. It really wasnt much hotter then it already was from the engine heat. I need to put some gauges on it to check it though, doesnt blow cool.

Thanks again for all the help.