On my 2000 4wd 4 door blazer the a/c is only working when it wants to. I ran a jumper wire to the compressor itself and it works fine. When raoperated normally, it works not at all or very sporadically. On occasion, the compressor will kick in and cool interior down or defrost, then will stop again for a long time. I pulled the switch panel on the dash and everything seems conected ok. Could I have a faulty switch? Can a new switch panel be purchased? Is there a test to determine if this is the problem?

 

Kinda sounds like the relay might be bad for it. I know on my 97 taurus the heat would come on and off, after we replaced the relay it was fine.

 

Hmm. I never thought of that. That would be the relay under the fuse block on the fender well I would assume?

 

If the outside temperature is ~38F or cooler, there won't be enough refrigerant pressure to close the low pressure switch and the compressor won't run. If the outside temperature is above ~38F and the compressor clutch is mostly off and the interior is warm, the refrigerant charge may be low. If the charge is adequate while the outside temp is >>38F and the interior is warm, the low pressure switch may be bad. The low pressure switch is usually on the refrigerant collector/dryer in the low pressure line (the fat cold one), and the low pressure switch may be replaced with no loss of refrigerant as there is a schraeder valve under it. Test the low pressure switch by connecting the two wires in the lead together after confirming charge level, temps, etc.
If this sounds mysterious, take it to a certified A/C servicer.
Hope it helps.

 

Heres a post about the relay
https://blazerforum.com/m_64546/tm.htm

 

Got through the house tonight and thought I would try jumping the wires on the low preasure switch. Popped the hood and started the engine on max cool. Although its 31F out, the compressor worked absoulutly perfect. On A/C or defrost the system cycled on and off with out a problem whatsoever and did so for 10 minutes(?). My daughter who drives it to school until I rebuild the starter on her mazda this weekend said the blower motor only works on 3 and 4 now. . I should probably replace the relay on the firewall to fix that problem.

 

Sounds like you either have a low charge or a faulty low pressure switch.

As far as the blower motor goes, if it works on 3 & 4, the relay is doing its job and you have lost the first two modes in the blower motor resistor block. The resistor block is located on the HVAC housing under the hood. I have posted an illustration before which should turn up through a search, but if it does not, let us know.