ptuttle

Hello,

My A/C does in fact cycle while driving. I first noticed this by a faint clicking (relay noise) under the dash. When looking into it (in my haynes manual wiring diagram) it appears that there is a frost warning temp switch.

Is this normal to cycle like this going down the road? or is it possible that the new stuff I put in is actually freezing the system?

I just charged it, replaced a line and put in a rebuilt compressor.
The A/C cools very well but not ever having an RX-7 with A/C before, I can't say its colder than before.

I was initially concerend (in another post) that the compressor did not cycle at all. But this was observed at an idle and not driving down the road.

If anyone could share how their A/C behaves, I would really appreciate it.
thanks

ptuttle

in doing some research and google on A/C problems; it sounds like I could have moisture in the system.

So I ordered a couple of cans from Enviro-Safe the removes the moisture. It was cheap enough, so I'm giving it a try.

I know I should bring to a perfessional; but that takes all the fun out of it.

mazdaverx713b

iTrader: (91)

my first suggestion would be to check the a/c system pressure. low refrigerant can cause cycling of the compressor.

ptuttle

UPDATE,

I tried the moisture resolution by using a can that is suppose to convert moisture to oil in the system. This did not make any diff.

So I have been doing some reading and think? the problem might be related to the slight over heating causing too much preasure and it's the preasure kicking the AC off while going down the road.

Again, I can be sitting at idle or reving the engine and the compressor does not cycle.

I have noticed that my temp guage goes to 1/2 while driving up a hill with the A/C on.
Typically the guage stays round 1/4 without A/C on.

I'm thinking I might benefit from an electric fan?
Question:

- What brand / model is recommneded for an 82. (82 has the smaller radiator with the oil cooler)
- Is the one Black Dragon Auto sells any good. I have also seen recommended on this
forum "Black Magic" but don't know where the best place to purchase these are.

Also, the preasure switch in the line....Is this for both "low" and "high" preasure.
I always thought it only worked for low preasure but not sure.

CHiNO84gsl

Not sure how the stock a/c on 7's work since i never had a/c in mine. But in most cars ive driven with a/c includding my old nissan max (vg30det t25 15psi) when ever i drove with the a/c on an I hapend to get on it or just be driving a little faster than evry one else the a/c comp would turn off and wouldnt turn back on till i slowed down im pretty sure this happens so the a/c comp doesnt get over worked and blow up but im not positive as I slept through most of class when we went over this stuff (Can get pretty boring Trust me).

Rx-7Doctor

iTrader: (13)

It is somewhat normal for a engine temperature to rise when climbing a hill with the A/C on. You are putting a extra load on the engine.

The things that contribute to the overall efficiency is the condition of the radiator (how clean it is inside) meaning if any of the passages are blocked. Whether or not you are using a Factory Mazda thermostat.If your radiator cap seal is good and holding pressure. How well your original fan clutch is working. Whether there are a lot of bugs or debris build up in front of the A/ C condenser and or radiator. Proper amount of coolant/water mix.

There is only a low pressure switch in the system. This is to keep the compressor from engaging and burning up if their is insufficient freon in the system.

I presume if you just switched the compressor that you are using R134A? You also should have changed the receiver drier. You need to hook a gauge up to the compressor and check the low side reading to determine the state of charge. The instructions come with the gauge and tell you what the pressure should be according to the outside temperature. It is normal for the compressor to cycle on and off while driving.

As far as a electric fan goes. Please do a search as we have covered that topic over a hundred times. Use the advanced search and use the option of seeing the replies with at least 20 or so posts to weed out all of the times that members have not used the search function on these beat to death topics. :-)

ptuttle

Thanks very much for the info RX-7 Doctor,

You answered one of my questions that it is normal for the compressor to turn on and off while driving.

This is good news as I thought there was something wrong.

But that leads me to another question that I cannot find anywhere on this forum or in my manuals.

What is the trigger to do this? Why is it cycling while driving?
I can sit in the driveway at idle or rev the engine or keep it steady RPM and it won't cycle
But drive down the road and it cycles often like every 15 to 20 seconds.

mazdaverx713b

iTrader: (91)

Pat, the pressure switch causes the system to cycle. check the system pressure with a gauge on the low side of the compressor.

ptuttle

Thanks for the info. I checked the low side and it's 45 at an idle. when increasing the idle, the preasure begins to go down. Not sure if this is normal or not? The A/C works great I was only questioning what circuit causes it to cycle only while driving.

coldy13

The A/C compressor is supposed to cycle. As the compressor pumps the pressure should drop on the low side, and when it get to ~20psi the compressor shuts off. The compressor should also shut off at WOT so it doesn't drain any power. How fast is it cycling while driving? Every 30-60seconds is normal or maybe faster at higher RPM, at idle if it's cycling more than once or twice a minute there may be something wrong. 20-50psi is normal on the low side and 150-220 on the high side depending on the outside temp.

When you change refrigerant you should drain the oil out of the compressor and fill it with the proper oil for the refrigerant your using. Mixing oils is bad and the compressor wont last as long, all the small recharge cans I've seen have oil mixed in. You should replace the receiver/drier but I've seen many converted without this and work just fine. Most of these were newer cars so if your a/c hasn't worked for a while I'd replace it since moisture has probably gotten in the system. Connect a vacuum pump for at least 30mins after opening any part of the system to get all the moisture out before recharging.

ptuttle

Thanks everyone for the explainations and advice. Very much appreciated.

mortiky

your system is most likely low on charge if it is cycling more than normal, especially if it seems more pronounced with higher rpms.