Overheating only with AC on

[94shodriver]

I just got the AC working in my car after a couple of years, the car is only driven part time. I replaced the leaking high and low pressure port schrader valves, vacuum purged the system and refilled with new refrigerant and oil. The AC system seemed to work well enough, it put out cool enough air for a comfortable cabin in 95* ambient weather. However, when moving slowly, not stopped but less than 50 mph, the temperature gauge creeps up to the top of normal and twice the coolant has bubbled out of the overflow bottle. Each time the radiator fans came on seemingly late and pulled the temp back down to "O" or there about before I shut down the car. I have not had any problems with it overheating with the AC off. Now when I turn the AC on, the compressor clutch activates and the fans kick in for 5 seconds or so before they turn off, then the composer clutch disengages after 30 seconds and another 20 seconds later the cycle repeats. The low pressure valve for the AC was just replaced as well. The whole engine was rebuild about 40k ago with all new sensors (except the CCRM), the radiator is about a year old, with maybe 2k on it. The radiator cap is new. I burped the system multiple times. I pulled the codes and they are 214 (Cylinder Identification Circuit Failure), 528 (Clutch Switch Circuit Fault), and 542 (Fuel Pump Secondary Circuit Fault). My clutch switch is disabled and I haven't had any fuel pump issues, I don't know where the 214 could have come from, the car runs great. The car is a 94 MTX 3.2 swap with ATX fans. I'm leaning towards a bad ECT or CCRM. Thoughts?

 

[rubydist]

ATX fans are two speed units - low and high. It sounds like only your high speed fan is running. You need to see if it is the fan unit or the ccrm that is not working right.

The low speed fan should be running all the time when the a/c compressor is engaged.

 

[94shodriver]

Solved it. The fans come on earlier and stay on with the AC. No overheating on a test drive that I overheated on two days ago in the same conditions. I replaced the ECT, apparently the old ECT was out of spec, and my MTX to ATX wiring was exacerbating the issue.

I need to wire in a third relay so that when the CCRM sends the command for high fan, both ATX fans come on, but thats for another day.

 

[rubydist]

the ATX fans are wired in parallel, which means they both run at the same speed as the other all the time. When on low, both run low; when on high both run high. If that is not happening, then you have a problem with the fan or wiring, which could be causing your overheating issue.

 

[94shodriver]

I have separate relays for the fans themselves. Somebody told me that they might draw too much amperage for the MTX CCRM. Not understanding how the CCRM output worked, I wired one fan to the high and one to the low outputs. Then switched both to just the high output and back again. Now I have realized that this set up means that only one fan comes on at a time. I'm going to add another relay to the second fan from the high output so that on high both fans come on. Regardless on which fans come with this set up, they always have full voltage. I might bypass or eliminate the CCRM altogether at some point as well. It seems like an issue waiting to happen.

 

[itwonder]

Glad you worked it out; The fans run on low whenever the A/C is on and the vehicle speed is less than 50 MPH.