Introduction

The Fiero was available with air conditioning all model years, 1984 through 1988. During that time, there were three compressors used: DA6, HR6, and V5. The DA6 compressor was used on 84 and 85 four cylinder cars, and 85-87 V6 cars, until some time in the 1987 model year, when GM changed over to the HR6 compressor, an improved version of the DA6, which was used on late 1987 V6 cars and 88 V6 cars. The following applies only to the DA6 and HR6 compressors, NOT the V5.

Being externally nearly identical, both the DA6 and HR6 compressors function the same way, and are interchangeable. However, the more reliable HR6 is recommended any time repair or replacement is needed. The HR6 is also rated for use with R-134A refrigerant when doing a retrofit.

Both compressors use two switches mounted in the back as safety devices: the low pressure cut-off switch, and the high-pressure cut-off switch. These switches are interchangeable between compressors.

Switch Functions

The low pressure cut-off switch is normally open. This can be tested by using a multimeter set to continuity mode. There should be no continuity between the large round metal body, and the contact on top of the switch. When pressures inside the compressor reach a certain point, the switch will close, and turn on the radiator fan. This is designed to increase airflow over the condenser, and lower the system pressure. The switch closes at approximately 280 psi.

The high-pressure cut-off switch is normally closed. This can be tested by using a multimeter set to continuity mode. There should be continuity between the large round metal body, and the contact on top of the switch. When pressures inside the compressor reach a certain point, the switch will open, turning off the compressor, disengaging the compressor clutch plate. The switch opens at approximately 425 psi, and closes at approximately 200 psi.

New VS Old Style Switches

For whatever reason, the old style switches are no longer available. They have been replaced by switches that use new connectors, and are no longer grounded through the compressor body. When changing the old switches out for the new style, one side of the new connectors needs to be grounded, and the other side connected to the original wiring. The new connectors may be purchased with or without the new style switches.

The two types of switches used originally in the Fiero were the red pin switch, and the white 'mushroom' switch. The red switch is the high pressure cut-off switch, and the white switch is the low pressure cut-off switch. The easiest way to remember this is the white switch controls the radiator fan, uses the same type of connector as the radiator cooling fan switch.



Both switches have been replaced by the following:

Santech part # MT0671
Santech part # MT0678

Both of the above include the switch, connector, o-ring, and C-clip, for ease of installation.

MT0671, replaces the low pressure (white mushroom) switch. It is normally open, and closes at 283 psi, and reopens at 210 psi. It is colored purple.



MT0678, replaces the high pressure (red pin) cut-off switch. It is normally closed, and opens at 430 psi, and closes again at 200 psi. It is colored blue.



Both switches include HNBR o-rings, typically green, that are both R-12 and R-134A compatible.

Replacement of the switches is the same as the originals: Remove the snap rings using snap ring pliers, and pull the switch straight up and out. Remove the old o-ring. Coat new o-ring in compressor oil, and place into groove in compressor. Push new switch into the compressor, and replace the snap ring.

Part Numbers:

All are Santech brand unless otherwise noted

Low pressure switch: MT0500
Low pressure switch connector: MT0135
Low pressure switch kit: MT0671

High pressure switch: MT0447
High pressure switch connector: MT0136
High pressure switch kit: MT0678

Switch O-rings: AC Delco part # 15-30999

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1984 Fiero SE

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Kevin87FieroGT (edited 07-21-2011).]

I stumbled through all this switch replacement business last year when I overhauled my A/C system.
http://www.fiero.nl/forum/Forum2/HTML/107037.html

2 terminal, high pressure cut-off switch from Factory Air / 4 Seasons, PART NUMBER: 35974 ($27.00)
2 terminal low pressure / condenser fan switch from Factory Air / 4 Seasons, PART NUMBER: 35969, ($29.79)

( Note that the color of the switch may be different from various manufacturers)

You might have to tinker around with connecting or disconnecting the ground wires, as I also had the problem of the constant running fan until I disconnected the low pressure switch ground wire. All works as it should since then and my A/C is still blowing COLD this summer.

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[This message has been edited by randye (edited 07-21-2011).]

quote Originally posted by sricka01: Bump. This question is directed to RWDPLZ and RANDYE. I have an 88 GT that had for lack of a better term an "explosion" from the engine area last fall. A hazy mushroom cloud effect, it was something to see! The compressor was making a bit of noise for several weeks prior to that. I inspected the hoses and they seem fine between the firewall and compressor fitting. The compressor has some seepage around the front clutch area, so I assume the compressor exploded or that one of these switches blew out of the plug. **If I buy a reman Four Seasons compressor, do they come with these switches installed or do I need to buy these separately? If they are not part of the package, how do you wire them in to the factory setup?

The switches are NOT included with the Four Seasons Remanufactured compressor.
You will need to buy the switches AND the new mating plugs for them.

To wire them into the OEM harness is fairly simple. You will just cut the original single switch wires on the car, (do one at a time so that you dont confuse the high pressure cutoff switch with the fan switch), and simply splice in one of the two wires from the new switch plug.
The 2nd wire from each of the new plugs is a ground wire and you should run each of these wires to a good ground on the chassis or engine block.

NOTE: It doesnt matter which of the 2 wires you choose to splice into the harness or run to ground. Both switches simply complete or interrupt a circuit to ground. The reason for the 2 wires on the new switch connectors is that the old single wire switches grounded through the body of the A/C compressor and the new switches do not. Therefore the separate ground wire is required.
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[This message has been edited by randye (edited 01-21-2013).]