Suction Throttle Valve

The suction throttle valve is a device mounted with the A/C Evaporator as a way to regulate the temperature of the evaporator without cycling the compressor on and off. The suction throttle valve was only present on R12-equipped Z32s (1990-1993) with automatic climate control. Manual climate control equipped cars and R134A equipped cars used a thermostatic amplifier to cycle the compressor on and off.




Function
The suction throttle valve acted as a sort of pressure regulator on the evaporator. As the A/C Compressor creates a suction on the low side of the evaporator, the temperature can be controlled by regulating (throttling) the pressure in the evaporator. To low a pressure will cause the temperature to drop and can cause the evaporator to freeze, while too high a pressure will cause the refrigerant to cycle poorly and cause the evaporator to warm up, decreasing the effectiveness of the air conditioning.

Failure

Writeup by DanZee on c_repair_783581.0.html zcar.com

Over time, the suction throttle valve often becomes clogged or fails internally, restricting refrigerant flow, sometimes completely. This often leads to a situation in which the high pressure side sees excessively high pressures, while the low pressure side sees excessively low pressure. This is in addition to little or no cooling occurring at the evaporator. Owners have noted that they can feel one pipe on the evaporator almost (or fully) frozen, while the rest of it is of ambient temperature.

Symptoms

• A/C diagnostic shows no problems with climate control or sensors.
• You get ambient temp air when the A/C is on full blast.
• Your compressor functions normally and your lines are cooling/frosting.

Diagnosis

1. Remove your glove box.
2. Remove plastic bezel from under glove box. (three plastic popout clips)
3. Remove two 10mm nuts from the bottom hinge of the glove box
4. Remove one #2 phillips screw from the spring/shock holder and remove the glove box.
5. Remove the fan feedback sensor (Large heatsink like unit) this is the two philips screws right in the middle behind the glove box.
6. Remove the feedback sensor, and feel the evaporator coils with your hand with the a/c fully on. It should be ice cold. If not it could be your Throttle Suction Valve.

Gutting

Because the part is no longer available, many owners opt to gut the suction throttle valve, essentially bypassing it and allowing coolant to flow by unrestricted. This should be done with caution, as it can cause evaporator temperatures to drop excessively. While rare, it is still a possibility, and it should again be noted that systems which originally utilized a suction throttle valve did so due to the lack of any other form to regulate temperature at the evaporator.

Writeup by DanZee on c_repair_783581.0.html zcar.com. Supplemented with photos courtesy of Adrian V.

1. Have the system fully discharged by a qualified shop.
2. Disconnect your high and low side lines at the firewall(right next to your battery.
3. Remove the 10mm nut holding the rubber gromet on the firewall between the lines (next to the battery)
4. Remove the rubber gromet (slides out with factory slits) and slide off the metal gromet holder.
5. Remove your glove box as above.
6. Remove your radio bezel, and shifter bezel and the passenger swede cover that goes from the glove box to the shifter.
7. Remove the swede trim on the passenger side of the glove box.
8. Remove the metal glove box frame on the face side of the glove box.
9. Remove the 3-10mm nuts holding the blower unit in place(one 10mm screw on top two nuts on the bottom)
10. Remove all electrical connectors (5 I think)
11. Work the blower unit toward the passenger side (4-5 inches)
12. Remove the three cooling unit nuts 10 mm.
13. Slide the cooling unit(the thing with the evaporator in it) to the passenger side and gently work it out.
14. Remove it from the car gently by sliding out from under the dash.
15. Once removed, there are several metal clips that pop off carefully with a screwdriver.
16. Separate the plastic housing from the evaporator.
17. Remove the expansion valve feedback tube from the throttle suction valve.(you will need to peel back the black tar crap to get at it.
18. The throttle suction valve is large and is the only thing on the evaporator unit that has two philips screw holding it in place (connected to one of the lines). Remove it by removing the two philips screws.
    
19. Put your thumb over the threaded portion of the TSV port, and stick an air compressor nozzle in the expansion valve port.
20. The TSV body should pop right out.
    
21. Installation is the reverse of removal.
22. Recharge system and have a shop check for leaks.