so I've known my AC thermoswitch was stuck closed (closed circut) for a while now. At times during long-term AC use the condenser would freeze over and I would have to turn off the AC by hitting the AC switch and to let it thaw. Recently I noticed the AC not working and I found areas where freon was leaking arround O rings between the condenser and the evap core (using UV light). Also the compressor is starting to make a weird noise even though theres freon still in the system although its likely low due to the leak.
I think its because the system keeps building to max pressure which is not what its designed to do so I'm gonna do what I should have done a long time ago and replaced that thermoswitch. One big problem, though; I cant seem to find a replacement anywhere. Only option I see thats even remotely close is the FB thermoswitch and I dont think the bolt holes are going to line up.

Anyone else have any other ideas? Has anyone modified the FB AC thermoswitch to work with the FC HVAC system?

 

have you verified it by checking the pressure differential in the system? if it is stuck closed you'd obviously have low side near vacuum or into it and excessively high high side pressure(200+PSI). components freezing up can also be as simple as a low charge(both sides would be equally low).

i also figure you mean the expansion valve, or are you talking about the pressure limit switch?

both parts are available at rockauto and other suppliers.

the pressure switch only cuts the system off when the low limit is met, it won't protect it from an overpressure condition and the system will rely on the a/c compressor pressure relief valve in that event. one problem i run into with some DIYers is they simply have no clue how much refrigerant is in the system and keep adding more, the RX7 has no safeguards for this scenario. i tend to think this may be the case when folks won't give pressure readings with symptoms like this, however a overcharge condition won't cause a evap core freeze up, it will make the system overwork itself. are you sure the core is even freezing?

i just feel like some things aren't adding up here.

after the car has set for several hours the static pressures should be around 85psi on high and low, with a properly working system low should be around 50psi and high should be around 150 or so, if the gap in the normal working pressures is much wider than that then it points to a blockage in the system, however your lines would both likely be warm to the touch after a bit.

 

So while the thermoswitch (I think) is stuck closed the AC pressure switch is working and is actually brand new. I would think if it was pushing all the freon into the high side I would have a line explode, correct? I have actually had that happen once due to a failed pressure switch so I dont think it would get anywhere near vacuum on the low pressure side simply because of the high pressure switch kicking the compressor off.
I personally havent seen the pressure differential as I dont have the equipment to do the AC recharge by myself but they never said anything was out of the ordinary. And this was done in the heat of summer. I do know that last time I was recharged they vaccuumed the system and left it overnight and it never dropped which is why I think its due to it running constantly on max pressure.

 

nope, the compressor has a bypass valve that will purge in the neighborhood of 300psi, the lines can hold more pressure than the purge rating. if this was done by a professional shop i might suggest trying another shop that may have more experience. if the expansion valve is stuck it will show up on the system pressures.

problem is the whole field of automotive repair now is filled with lots of rookies, who don't know how to actually diagnose a system with an issue. sometimes problems can exist with as little as a 20psi off normal reading high or low, good enough doesn't apply to air conditioning systems.

if the pressure differential is too narrow it points to compressor failure.

 

well it was back in florida and I'm up in TN now so I have no choice but to find someone else. But what you said doesnt really make much sense, How would an AC line explode if the AC compressor has a purge valve that opens at 300psi?

To add further context. I have had one situation where the bolt in the back of the denso compressor blew out stripping every thread in the compressor because of high pressures. That was years ago. more recently, I had the high side AC compressor hose explode on me so im not sure about this bypass valve your reffering too.

 

are you saying you had a line explode? it certainly is possible but it shouldn't happen if the lines are in decent working condition. both high and low side have rubber incorporated lines which can become weak over time and unable to hold all the way up to purge pressure. basically if the car was relatively new, the lines could never explode, but dry rot of rubber is a thing.

 

basically what i mean is the system was designed initially so the lines couldn't rupture but instead vent excess pressure before it happened. but the cars are older now, and that is certainly a possibility. it would also be a symptom of either a severely overcharged system or a stuck closed expansion valve.

 

I mean they were factory but the car was mint when I got it and its been garage-kept ever since. If it was dry-rotted, theres no way you would have noticed.

 

and reguarding low freon potentially causing the freezing up, I highly doubt thats the issue, as not only would the system hold vacuum over night but even the day after I had it charged it would freeze up causing me to have to toggle the AC switch and let it thaw. the AC worked like this for 8 whole months before I noticed a complete loss in AC performance when I pulled it out of storage a few weeks ago.
I think august of 2023 was when I had it charged last back in florida. I moved up to TN in april and the last time I drove the car was december of 2024 and between when I charged it and the time I put it in storage I had no AC issues.

 

you say vent, like atmospheric vent? or in system?

also more added context. it is running r134 and I had a parallel flow condenser installed in 2023 which was when I had the last recharge.

 

personally i would just recommend getting a gauge set so you can try to get some readings yourself. the tool would be useful for avoiding paying a shop to basically do the same thing.

something like this:


harbor freight also carries them.

 

the cars had atmospheric vents in the old days, newer systems have high limit pressure switches as well as the low limit switch, ours only has a low limit.

 

do the refurbished denso compressors still have the vent?

And reguarding the guages,I'll definetly give it a try. I've just left it to other people as I had kind of a paranoia when working with AC system. I learned to use these when I went to school to get my ASE certs but that was almost 4 years ago and i havent touched one since. Figured if someone else screws the pooch they pay for the repairs which has happened, just on other things.

 

Think we have a disconnect here. I'm not reffering to the expansion valve or the pressure limit switch. I'm reffering to the thermostatic switch inside the evap core box. It is specifically to counter the evap core from freezing over as it measures the temperature arround the core. when it gets cold enough to start freezing the switch will open causing the compressor to lose ground and shut off:

 

the nippondenso has the purge valve on the hose adapter block, the sanden unit has it screwed into the compressor itself.

most nippondenso compressors do not come with this adapter installed.

 

top is the nippon, bottom is sanden.

 

Neither of these look like the compressor I have and the one I have doesnt have what you circled so I question if mine even has it. Also see my previous post, this is the switch I'm reffering too:

,

 

i will have to look into how this switch functions, personally i have never had any issues with mine. it's possible you have a logicon issue instead of this switch. the logicons are susceptible to bad solder joints like all our electronics are. it's obviously a evap core temp sensor, many cars have them but i've never seen it cause an issue on an FC yet.

 

its not a logicon issue. Trust me on this, its not. I have a Microtech ECU which does not have AC inputs and had to make custom wiring to run the ground for the AC compressor on a separate switch that grounds through the thermo switch and the high pressure switch in series. if either trip it cuts ground and turns off the compressor. Its also run in series with the blower motor so if thats turned off the compressor turns off too.

The high pressure switch works, I've confirmed that. the thermoswitch I am 99% sure does not as the evap core will ice over and the AC compressor will still be running.

This brings me back to my origional question, does anyone know where I can get a replacement?

 

i'm wondering if you have a full retrofit kit from some supplier for the conversions. the denso kits installed by mazda should look like the one above.

 

at this point in time i think your only option to find a replacement is to find someone parting out a car. most parts fiches for the FC don't even exist anymore because the parts have long since been discontinued, like the a/c lines and compressor for example.

 

or alternatively get creative and find a replacement that functions the same as this one and try to mount it without disassembling the whole dash to get the air distribution box out. it looks like this would require all that, and these dashes are very crumbly. the plastic they used to make our dash was never meant to last 30+ years, hell they started shattering after 10.

 

Either that or try to retrofit one of these but I have no clue how im gonna be able to make this fit.For 1979-1985 Mazda RX7 A/C Thermo Switch 32286BNPY 1980 1981 1982 1983 1984 | eBay
Its for an FB, and I have an 87 so maybe theres some parts overlap but the bolt holes definetly dont line up when comparing the diagram I previously showed (if its even accurate)

 

being the FB used a very similar system as our nippon ones, it likely should work but mounting would require a little creativity.

 

I'll post an update here when I get it removed. also, on the subject of my AC compressor, this is identicle to the one I have in the car: 1986-1988 MAZDA RX7 RX-7 AC A/C HVAC COMPRESSOR OEM | eBay