200 psi is the target for R12 - 70 degree and higher ambients. With subcooling, what's flowing through the Condensor is a little over a 100 degrees. That squirts 30 - 32 psi into the Evaporator and the vent will be in the low 40's. Reduce the high to 180 and all you do is cycle the compressor as there won't be enough oomph through the orifice. You need to look at the High and the Low - note ambient or air temp at the Condensor. Make sure the system is on max and the engine is steady at 1500 rpms. If you've converted to R134, reduce the total charge to maybe 75% of the R12 capacity to keep the high in check when it's 90 or more outside. Run the Aux, Main and A/c and you'll overwhelm the 25 amps you've got pumping out of the alternator. Fans will slowdown, high side will go through the roof. It could overheat and trip the High Limit (or blow a hole in the hood).

 

I think I have a similar issue and the PO installed a Hypertec chip but somehow ended up with either a 180 or 195 Tstat. I was running hot and installed a temporary override switch for the main fan for when in traffic or running slow. The AUX fan seems to come on as it should. If the fusible link has "burned", how is that corrected?

 

Location of Fusible Link depends on Year - Starter or behind the Battery.

Link is sized to handle the Load. If it burns up running the Fan, the Fan Motor is drawing too many amps - usually anything over 10 or 12 means it's time for a new one - check it with a DVM or Clampon. Or there could be a loose connection causing it to drop volts which heats up the wire and burns it. If it's discolored at any connector, that's usually the case. Tighten it up - replace weatherpak and make sure the connectors aren't deformed. Assuming it's the way it left the Factory, it can and should run all day long and not burn up anything. If it didn't, a lot of C4's would have burn to the ground long ago.

 

It's an 85' w/Z51. I noticed that the wire I ran for the temporary switch (which I think is # 10) gets pretty warm at the switch. What problem is there in running a 160 Tstat?

 

One assumes you have the switch on the fan itself and not controlling the relay as you are supposed to do?
A relay lets you run full batt power to the fan without a long wire run through the switch ; which uses up power (voltage drop ) and heats your wire up

 

You are absolutely correct! I was beginning to troubleshoot my own problem and correct the wiring of the switch to control the relay and indeed I found a small melted plastic mess that looks like it used to be a fuse holder. UGH! I suppose I need to go back to a 160 t'stat or try to find an OE chip. What is the harm in using the 160?

 

After searching and reviewing many threads on the topic, I see that there are many thoughts and opinions regarding the Hypertech and different t'stats. I am curious though as to why the fusible link burned from using the 195 stat. I would think that a simple on/off relay circuit to a fan would not care what the temp is. the fan is either on or off. What would cause it over load the circuit?

 

Worn out fan motor or a loose connection.

 

The fan is relatively new and still curious re: the previous post that stated running 195 vs a 160 would burn the link.
I'll check connections and try to locate a clamp on meter to measure draw.

 

Make sure you have the right size Link too, expecially if there's any sign that someone has changed it out. Refer to Manual Schematic for gage.

 

My manual shows .5 Orange with a 3 Red to the relay. How can tell what gauge link to use

 

I just read this whole thread. Some of this has been mentioned.
1. Just because the radiator looks clean does not mean the tubes are not clogged up.
2. You should never have the main fan coming on before the stat opens up. You have a fan running much more than it should. Plus, if the stat is not open, there is none or minimal flow so the fan is doing nothing.
3. What I would do. Hypertech sucks. Get a chip programmed so the fan comes on at about 195 and put a 180 or 185 thermostat in it. Then get a stock switch for the aux and leave it alone.
4. Install a DeWitt rad.
5. Be happy
IMHO Your mileage may vary.

 

Because there is a chart showing (converting) from those .5, .25, etc... markings to a specific wire gauge. I don't recall where, in the FSM, it is, but it's there. My first thought is on the pages at the beginning of the schematic section.

 

A properly charged and functioning a/c system makes pressure instantly. If it's temperature (pressure) isn't controlled by the fan, it trips the High Limit or blows a hole in the hood and that's pretty much true under all ambients though at around 50, the fan is on a great deal less. Those that don't have the fan running are broken (or soon will be).

The average Condensor temp/target for most mobile systems is about 100 degrees/200 psi, but that is going to vary with air temp and gas. Thats why the Condensor sits in front of the Radiator. If you want to do the math, see what is, get a pressure/temp chart and performance specs for your car out of the Service Manual. Also note the ECM threshold for grounding the fan(s) relay. If you want to see what all this is for your Home Unit, chart should be on the inside of the Case though it is going to reference superheat and subcooling (important concepts, but never really relied upon by mobile a/c folks).

The stat is used to maintain appropriate operating temp. With a/c, it would take longer to get there without the thermostat because the fan is on sooner and stays on longer. In fact, some modern designs - mostly trucks and SUV's, rarely run the fan at all - except with the a/c. The large open grill provides an incredible amount of heat transfer under more conditions than a bottom feeder like a Vette. These same designs use up to 3 fans or different speeds to maintain the refrigerant at the proper temp/pressure. Hybrids with standalone systems and stoplight engine off cars (BMW for one), just use a dedicated fan for a/c.

There are tools to measure wire gage (usually built in on cheapo Crimpers) and factory fusible links are marked though that marking may be long gone.

 

Found it, it's in the Electrical Diagnosis/Repair Procedures section. Kinda odd that they would use metric wire size in 90.

 

Why?
The C4 has all Metric fasteners ;the only Imp threads in the car are on the carry over engine

 

Still looking for info on why using a 195 vs a 160 would burn the fusible link. I replaced the link and the fan runs fine when I ground the relay.
Anybody......????

 

Because it doesn't. Sometimes the information that's posted around here is wrong. If you want to learn more about electrical circuits, pick up an electrician's handbook at Home Depot. Though it's geared toward the home, all the basic stuff is applicable to your vehicle's wiring. It will give you charts/info on types of wire and ampacity, circuit protection, etc. Electrical defects/shortcomings in cars are usually caught during the warranty or by Recall. C4 wiring problems, given the age, allmost always have to do with increased resistance (rusted terminals, corroded copper wiring and open grounds), insulation failures, and just plain old worn out parts that use electricity or electrical principals to operate or sense some sort of event that the ECM uses to deliver fuel.