Cooling fan, A/C and IRCM problem

ruswin

Registered User
I was in the process of charging my A/C system in my 90 when the cooling fan and the A/C clutch stopped working altogether. While I was charging the system, it did not seem to be taking the refrigerant correctly, the clutch was cycling On/ Off at regular intervals without changing duration, and the motor started bogging down. After about 10 minutes, the clutch stopped cycling and the cooling fan stopped running.
As stupid as this sounds, I was having a hard time identifying what fuse protects the cooling fan when I found a bunch of info on the fuseable links. I still am not clear which fuses control the fan? I also don't understand why at the same time the fan quit, the compressor clutch also stopped cycling.
I checked other threads and verified the fusable links were Ok (I think) and that the IRCM was getting 12v power on wire #38 blk / org and the wire #57 blk was grounded. Could the IRCM have just gone bad? I have a 93 IRCM, can I swap it out with the one in my 90 to check it?
I also looked for threads about reparing the IRCM, does anyone know if they are potted or even if they can be opened and serviced?

Last question, is the IRCM for the SC different than a standard 3.8 liter t-bird? Thanks...
 
You were right, to a certain extent. I read the other thread you mentioned and checked the switch on the receiver / dryer. When I jumped out the switch, the fan came on as did the clutch. The IRCM is fine. So I continued to charge the system, and actually now have it blowing pretty cold at 45psi low side pressure.

My first question is "what is the switch on the dryer reciever, hi or low pressure"? The Chilton manual says A/C pressure switch or clutch cycling pressure switch. Where are the low pressure and high pressure switches located?

The second question is, will it damage the system to keep that switch jumped out? If it is the high pressure switch, won't the pressure relief valve on the compressor continue to protect it from over pressurizing? I have had the pressure relief valve open on the top of the compressor to relieve pressure on another SC with no problems afterward. (The cooling fan was not running at the time causing the A/C to overheat and blow off some refrigerant)
 
>My first question is "what is the switch on the dryer reciever, hi or low pressure"? The Chilton manual says A/C pressure switch or clutch cycling pressure switch. Where are the low pressure and high pressure switches located?<

That is a low pressure switch on top of the dryer.
Our A/C system does NOT have an electric OEM high pressure switch.

The 'low pressure' switch/ clutch cycling pressure switch is used to prevent the expansion valve/evaporator from getting to cold/damage . From the Ford manual (attached) when temps over 90F it appears to not cycle, but under 90F should cycle 10- 100 seconds page 36-31-9 & 10 depending on ambient temperature. So it would probably be OK to jump it during a hot day 95+, but NOT at night 95-.

I was not aware there is a pressure relief valve on the compressor. (overcharging? Did the system work afterwards? It would be interesting to know what pressure the the HP saftey valve worked)
I have read that excessive 'cycling' will overheat the compressor because the oil is cooled by the suction side, (to much cycling>not enough oil>overheating) To much cycling can also be caused by low freon.
For more info checkout forum at www.ackits.com

Perhaps you have a defective low pressure switch, or low pressure?
You already know, but for those who don't, one should pull a vacumn with a special pump before freon can be added. Or you better be sure your can of freon has a higher pressure then the suction line, something like that.
 

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I would have to guess the switch is bad. The A/C seems to be running fine, it was reading about 48 on the low side while running. I am concerned that if I leave it jumped and then I end up leaking all the refrigerant out, I will fry the compressor.
Do I have to evacuate to change out the switch?

How much pressure should I have in the system when the unit is off and cooled down? I want to periodically check it for leaks.
 
You don't evac, you recover, then re-use.

you should get a set of gauges on there so you can read high and low pressure. You may have overfilled it.
 
ruswin said:
"what is the switch on the dryer receiver, hi or low pressure"?
Both (so to speak). This switch needs ~45 PSI to trigger on, and will only trigger off when the pressure falls below ~26 PSI. Late model A/C systems use a high-side pressure switch that disables the A/C compressor if excessive pressures are reached (~425 PSI or so), but our early SC's don't have this.

ruswin said:
Do I have to evacuate to change out the switch?
No.

ruswin said:
How much pressure should I have in the system when the unit is off and cooled down? I want to periodically check it for leaks.
It doesn't work that way (as I have recently discovered). Once you have a minimum amount of refrigerant in the system, the static pressure is directly related to the type of refrigerant used and the ambient temperature (Look it up on the appropriate pressure-temperature chart for that type of refrigerant).

ruswin said:
I would have to guess the switch is bad.
Sounds like it.

sail7seas said:
It would be interesting to know what pressure the the HP safety valve worked
It opens at pressures above ~450 PSI.
 
It seems some times, I make things more complicated than they must be. After further testing, it seems the system was working EXACTLY as it should. The low pressure switch was originally cycling On / Off when I was first trying to charge the system. I did not jump out the switch which I think caused a problem and ended up shutting off both the fan and the clutch after 3-5 minutes of cycling. When I disconnected the low pressure switch and jumped it out, the fan and clutch started working again. (Have no idea why?) :confused:
After that, I found that the cheapo gauge I was using was wrong indicating the the system was full when in actuality, it was still about 14 oz low. Once I fully charged the system with a better gauge, everything works perfectly. A couple of notes:

1) I assume it is OK to jump out the low pressure switch while charging to eliminate the clutch cycling ON / OFF?
2) Using a good gauge set is important for accurate measurements. :rolleyes:
 
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