Automotive Air Conditioning Information Forum

Thermo Switch or Evaporator Switch Question.

Short Back Story.

1990 Mazda B2200 AC all parts took apart, cleaned and put back together, new drier and compressor and using Duracool.

Worked great, till my evaporator had a leak in it at the suction side connection.

When I say worked great, I mean 95F ambient and heat index of 114F and vent temps reaching 36-38F
It cycled beautifully. There is a thermo switch on the side of the evaporator case and its designed to cut the compressor off at 33.8F and I believe it did that just fine.

I have two of these trucks and they both work the same.


Now present day.

I had an extra evaporator and I cleaned it up and had it ready to go with all new Expansion Valve in place. I put in it, charged it up as I have done many times and all was working well ACCEPT it was not getting as cold, or it would, it would just take longer because of the thermoswitch, turning it off at 46F and back on at 55F (vent temps).
This was not what it had been doing, plus it was sort of stinking like a water funk.

So after many adjustments and things that claimed to take smell away, I decided to just order a NEW evaporator and try again.

Brand new evaporator in place, no stink, all parts in place and its doing the same thing.
Instead of cutting off at 38F vent temp, it consistently turning off at 48F.
I decided to see if it was the thermoswitch and used a wire to bypass it.

When its bypassed, it gets the vents down to 35F, of course because its freezing down there.


I can't understand why both of my (known good) ThermoSwitches are doing the exact same thing.

It is not hard to install and I have placed them in the exact spot where they go and its done it to me twice. Its like its 10 degrees off in both directions.

Any tips or ideas?

Should I order a new one that has an adjustable dial?

This is the current switch part number, its by Ranco
a10-7071-000



https://pasteboard.co/JrcrWWL.png

Yes I am sure its in the right place. There is mark where it goes.

Its such a pain to deal with this evap case under the dash.
I may unclip it and see if I can adjust the probe and see, but I feel like it will be the same.
I was thinking about an adjustable one, like if I have to go in there at all, I was thinking of putting one in that I can fine tune and be done with it.

I have put AC in and out of these trucks many times and can not for the life figure out why all of a sudden the thermoswitch, two of them, are acting the same, and now allowing it to get colder.

Try setting the depth of the probe at different heights.

I dread taking the bottom of the evap case apart, but I will do it and move it really close to the top and see what happens before I order an adjustable one.

digeratimvp wrote:I dread taking the bottom of the evap case apart, but I will do it and move it really close to the top and see what happens before I order an adjustable one.

Wear eye protection and don't lose any of the little clips holding the bottom part on !!!

Ok I had never done that before, taking the bottom of the evaporator case apart under the dash, but I did it.
It was not easy.

I moved it up and no change.

So I connected gauges once again and this time it looked to me like the expansion valve was at fault and to me that would explain why my two efforts and then even the relocated probe, did nothing.

So I took it apart and put a new one one, and reassembled, pulled a vac, charged and guess what....
SAME THING!

But the pressures and all read good. Its just cutting off too soon.

So I am thinking of ordering an adjustable one, OR I might go in one more time under the dash, and a take the probe OUT of the evap coil, and just let it rest on the outside of the coil on the side that faces the vents, right up on the evap fins, and see if it will work.

I really almost hate to do it that way. Might just wait on an adjustable one so that I am under under there hopefully once.

please post your pressures at 1500 rpm

On a MACS forum always post pressures

Ok today, I took a break from it, but yesterday, best I can recall after it was running for about 5-10 mins and it was 87F outside I think, the readings were
30 Low side
200-225 High side with no fan in front of condenser.

Tomorrow I may take new readings to be certain.

I am running Duracool which is a solid r12 replacement but it takes a lot less.

This truck if it were to have R12 in it, states the pressures should be as follows if it were 77F outside.
ORIGINAL PRESSURES WITH R12
Ambient temp 77F
Low Pressure 14-24 psi
High Pressure 149-185 psi

So with the duracool, I do find it runs pretty good at 25-30 L and 200 H
I have installed AC from scratch in 3 Mazda B2200 pickups and its always worked out fine this now for me.

Even though I have been successful with it, I am by no means an AC genius and can always learn something new.

If you're in the US. duracool (HC) is not a legal R12 replacement. I don't have control what people use as a refrigerant. But readers should not think this is a R12 replacement.