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1985 Reliant A/C questions

Discussion in 'EEK! - Every Extended-K Car' started by twankowski, May 8, 2020.

  1. twankowski

    twankowski Active Member

    Oct 29, 2011

    Still pending some pressure readings on the '89 Sundance I posted about earlier, but now have a question about the system on my '85 Reliant. This car has proven to have a few attributes that are different from my Daytona and the Sundance (such as the early Bosch TBI unit).

    Anyway, decided to completely replace almost everything in the A/C system, if for no other reason than it'll be less [I should have my mouth washed out with soap for using such terms]-pain and will look cleaner/better. That said, looking for info on the following parts which are different from all the other cars on which I've done R134 conversions.

    First, while the expansion valve is very typical and has the usual 2-prong low-pressure cutoff switch mounted on the driver side, there is also what the parts manual calls a "SWITCH & LUBE PKG., A/C Suction Line Temp. Sensing or Cycling" screwed to the side as well. Mopar part number 4339411. Looks like this:

    The copper probe slides into a "well" on the suction line a few inches from the expansion valve. On the existing setup, the probe looks like it simply slides into the well and just sits there. There is some grease/paste present, but after 35 years could just be crud.

    So, does the probe simply slide in the well and sit there? Any dielectric grease or similar needed?

    Also, what does this actually do? From the part name it senses temp, but what for? Haven't seen this before and want to set it up correctly.

    Furthermore, while I'm building my parts list, both the parts manual and the Rock Auto website show a high-pressure cutoff switch. Mopar part number is 3848674. Looks like this:

    This part apparently threads inline someplace, but just looked at the car again and I don't have this any place on the system. Interestingly, the parts manual shows this part under the exact same numbered part on the diagram as the low-pressure switch:

    upload_2020-5-8_11-6-26.png upload_2020-5-8_11-6-54.png

    The illustration is obviously the low-pressure cutoff.

    So does this mean the car has either one or the other? I sure as heck don't have the pictured high-pressure switch.

    I like to replace everything possible on these retrofits. New parts are clean and provide piece of mind.

    Thanks for any advice/info!
  2. AllanC

    AllanC Well-Known Member

    Jan 6, 2003
    What does "replace almost everything" mean? Specific components????

    This device is the air conditioning compressor clutch cycling switch. On a 90+ deg F day and with the engine idling, you most likely would NOT need a compressor cycling switch to disengage the unit. The compressor output would be matched closely to the heat absorption in the evaporator. But on a day with lower temperatures and driving at highway speed, the compressor has more than adequate output to lower the temperature of the evaporator below 32 deg F. So you would get icing of the evaporator, reduced air flow and eventual lack of cooling. So a cycling switch is necessary for these occasions to prevent evaporator freeze up / icing.

    The probe senses the temperature of the evaporator output line / suction line. Ideal design for this line is slightly above 32 deg F. When it drops below 32 deg F then it will open the circuit at the 2 contacts and de-energize the electric clutch. This switch is wired in series with the compressor clutch and low pressure switch. It probably used a thermal conductive paste in the tube well location. I think you could insert some insulation in the tube well to ensure that the probe had good thermal contact with the suction line.

    This high pressure switch is an addition for converting an automobile R12 air conditioning system to R134a refrigerant. Electrically it splices in series with the power and ground cable to the compressor clutch. It has a threaded fitting that mates to the high pressure port on the system discharge hose. Idea is to protect the C171 compressor from extremely high operating discharge pressures associated with a R134a refrigerant conversion. Is this high pressure switch absolutely necessary? No. Good idea? Yes.

    If you install this high pressure cut off switch you will have to install it over the existing fitting for R12 usage. When you want to check the system suction and discharge pressure, you will have to remove this pressure cut off switch from the discharge port and then attach the proper R134a discharge conversion fitting / quick disconnect so you can attach an R134a manifold gauge set. This might become an annoying hassle.
    Bob Lincoln likes this.
  3. twankowski

    twankowski Active Member

    Oct 29, 2011
    Excellent information, AllanC. Helps a lot. I plant to replace everything except the evaporator and condenser. The car still had a small quantity of its R-12 charge when I got it (compressor cycled, but quite rapidly). I had a bud capture the little bit left in there and will start R&R later today. The OE condenser looks absolutely beautiful, so if it flushes cleanly and doesn't leak it'll stay. I did this on my '86 Daytona in 2011 and it still blows nice & cold. Ditto for the evaporator...although I have the dash completely out of the car, so wouldn't be a big deal to change that & the heater core if need be.

    I got most of the replacement parts from eBay and Rock Auto, so wasn't very expensive at all. New compressor, expansion valve, low-pressure switch, both suction & discharge lines, receiver-drier...and now I'll pick up the high-pressure cutoff (thanks for the explanation on it's obvious how it splices into the compressor's power cable). The suction line with the well was challenging to find, but eventually got one for a pretty good price.

    Could probably re-use most of the components, but everything under the hood (and under the front of the vehicle for that matter) is so caked with decades of oil & filth that I'm getting dog-tired of scrubbing. This car leaked oil, ATF, and coolant from almost everywhere imaginable. Easier for me to replace low-cost items at this point, and will look 100% better with new stuff.

    Thanks again! Great info.

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